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Journal of Geographical Sciences >

2017 , Vol. 27 >Issue 11: 1389 - 1412

DOI: https://doi.org/10.1007/s11442-017-1442-0

Research Articles

Chinese progress in geomorphometry

  • LV Guonian ,
  • XIONG Liyang , * ,
  • CHEN Min , * ,
  • TANG Guoan ,
  • SHENG Yehua ,
  • LIU Xuejun ,
  • SONG Zhiyao ,
  • LU Yuqi ,
  • YU Zhaoyuan ,
  • ZHANG Ka ,
  • WANG Meizhen
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  • 1. Key Laboratory of Virtual Geographic Environment, Ministry of Education of PRC, Nanjing Normal University, Nanjing 210023, China
  • 2. State Key Laboratory Cultivation Base of Geographical Environment Evolution (Jiangsu Province), Nanjing 210023, China
  • 3. Jiangsu Center for Collaborative Innovation in Geographical Information Resource Development and Application, Nanjing 210023, China
  • 4. School of Geography Science, Nanjing Normal University, Nanjing 210023, China
*Corresponding author: Xiong Liyang, Associate Professor, specialized in digital terrain modelling and analysis. E-mail: ; Chen Min, Professor, specialized in geographic modeling. E-mail:

Author: Lv Guonian, Professor, specialized in GIS and virtual geographic environment. E-mail:

Received date: 2017-07-19

  Accepted date: 2017-08-09

  Online published: 2017-09-07

Supported by

National Natural Science Foundation of China, No.41671389, No.41631175, No.41601411, No.41371424.PAPD, No.164320H116

Copyright

Journal of Geographical Sciences, All Rights Reserved
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Abstract

Geomorphometry, the science of digital terrain analysis (DTA), is an important focus of research in both geomorphology and geographical information science (GIS). Given that 70% of China is mountainous, geomorphological research is popular among Chinese scholars, and the development of GIS over the last 30 years has led to significant advances in geomorphometric research. In this paper, we review Chinese progress in geomorphometry based on the published literature. There are three major areas of progress: digital terrain modelling methods, DTA methods, and applications of digital terrain models (DTMs). First, traditional vector- and raster-based terrain modelling methods, including the assessment of uncertainty, have received widespread attention. New terrain modelling methods such as unified raster and vector, high-fidelity, and real-time dynamic geographical scene modelling have also attracted research attention and are now a major focus of digital terrain modelling research. Second, in addition to the popular DTA methods based on topographical derivatives, geomorphological features, and hydrological factors extracted from DTMs, DTA methods have been extended to include analyses of the structure of underlying strata, ocean surface features and even socioeconomic spatial structures. Third, DTMs have been applied to fields including global climate change, analysis of various typical regions, lunar surface and other related fields. Clearly, Chinese scholars have made significant progress in geomorphometry. Chinese scholars have had the greatest international impact in areas including high-fidelity digital terrain modelling and DTM-based regional geomorphological analysis, particularly in the Loess Plateau and the Tibetan Plateau regions.

Key words： geomorphometry; digital terrain model; digital terrain analysis; progress; China

Cite this article

LV Guonian , XIONG Liyang , CHEN Min , TANG Guoan , SHENG Yehua , LIU Xuejun , SONG Zhiyao , LU Yuqi , YU Zhaoyuan , ZHANG Ka , WANG Meizhen . Chinese progress in geomorphometry[J]. Journal of Geographical Sciences, 2017 , 27(11) : 1389 -1412 . DOI: 10.1007/s11442-017-1442-0

1 Introduction

Terrain is considered one of the most important natural geographical factors. Explicit analysis of terrain is the core focus of geographical research, and it is important in geomatics, cartography and geomorphology. With the development of geographical information science (GIS), terrain research has undergone a revolution from qualitative surface description to quantitative terrain modelling and analysis. Terrain research now relies on digital terrain models (DTMs), which combine the digital expression of surface morphology with digital information on terrain for geo-analysis and have been used to simulate the earth’s surface (Tang et al., 2005).
Geomorphometry is the science of digital terrain modelling, analysis and quantitative land surface analysis (Hengl and Reuter, 2008). It is considered a digital information processing technology for calculating terrain derivatives, extracting terrain features and conducting geo-analysis based on DTMs (Zhou and Liu, 2006). Many studies in earth information science have focused on the basic theory, methodology and applications of geomorphometry. After several decades of research, many of the basic theoretical problems of geomorphometry (including digital terrain modelling, DTA methods, and the accuracy and scale of DTA) have been addressed, and DTM-based DTA theory and methodology have gradually matured. At the same time, the advantages of DTMs (such as their simple data organization, direct expression of terrain, easy and effective extraction of terrain derivatives, and diversity of data sources) have led to the application of DTA methods in many domains of geoscience, including geomorphology, hydrology, and soil science. These DTA methods also have societal uses such as surveying and mapping, water and soil conservation, the monitoring and control of hydrogeological disasters, and land use planning and management (Tang, 2014).
In recent years, Chinese scholars have made significant progress in geomorphometry research with the support of various funding agencies, especially the National Natural Science Foundation of China. In this paper, we systematically summarize and analyse research achievements and progress in the field of geomorphometry in China. First, we summarize DTM methods, including both traditional and more recent terrain modelling approaches. Second, we discuss various DTA methods to achieve a comprehensive understanding of geomorphometry. These methods are not confined to traditional DTA methods of extracting terrain derivatives and geomorphological and hydrological features; they also include methods for analysing strata structure, ocean dynamics and even socioeconomic spatial structures. Third, we review the applications of geomorphometry to demonstrate the capabilities of DTA. Based on these achievements and progress, we also discuss the future direction of geomorphometry.

2 Methods of digital terrain modelling

2.1 Traditional data models and structure

2.1.1 Vector-based digital terrain modelling
DTMs have been defined as the digital simulation of land surfaces using limited surface elevation data; they are also called digital elevation models (DEMs) (Tang et al., 2005). Wang et al. (2004) summarized the data models used in DEMs and classified them into six different types: discrete point-based, contour-based, triangular irregular network (TIN)- based, profile-based, grid-based, and hybrid DEMs. The first four types are vector-based DTMs, the latter two are raster-based DTMs.
Among the vector-based DTMs, discrete point DEMs involve a terrain model in which the surface is expressed as discrete points; each point is stored and organized based on its x, y and z coordinates. Contour DEMs are mainly digitized from existing topographical maps in which the elevation is recorded by contour lines. TIN DEMs are a type of model in which elevation is recorded using a triangular irregular network composed of nodes, arcs and polygons. TIN DEMs rely heavily on the use of triangulation algorithms. Many triangulation algorithms and methods of rapidly updating them have been proposed for the construction of TIN DEMs in China. These include the mathematical morphology-based approach (Li and Chen, 1990) and the constrained data set-based approach (Liu and Gong, 2001). Finally, profile-based DTMs record the coordinates of points on the profile using either varying distance intervals or the same time intervals.
Currently, TIN-based DEMs appear to be the most appropriate vector-based DTM method for describing the true surface of a terrain because they can preserve detailed terrain information by using both hard and soft lines. However, the complex data structure and calculations required by this method, as well as the difficulty in integrating the method with remote-sensing (RS) imagery, means that vector-based DTMs are always converted or interpolated to raster-based DTMs.
2.1.2 Raster-based digital terrain modelling
Raster-based digital terrain modelling involves organizing an area into a series of cells that are distributed in space. These cells are generally regular grid cells or spheroidal equiangular cells (Florinsky, 2017). Regular grid-based DTMs are now the most popular type of DTM. This variety of model records the elevation (z) as the attribute of the cell and stores the x and y coordinates as the row and column numbers of a matrix. The data structure of regular grid-based DEMs has been widely accepted because of its simplicity, ease of storage and easy integration with RS imagery.
Most regular grid-based DTMs are constructed using interpolation and digital photogrammetry approaches. Chinese scholars have contributed significantly to both approaches. Interpolation can be divided into global interpolation, local interpolation and point-by-point interpolation (Tang et al., 2005). The global interpolation method is rarely used in constructing DTMs because it is concerned with large-scale terrain features and ignores local terrain characteristics. However, many local interpolation methods have been proposed by Chinese scholars, including the dual spline function (Wang et al., 2000), the Coons surface (Chen et al., 2012; Wang et al., 2008), and the polyhedral function (Lv, 1981). Research on point-by-point interpolation has mainly focused on the selection of interpolation functions and the determination of input parameters and weights (Dong et al., 2013).
In addition to the traditional interpolation approaches described above, other interpolation approaches for constructing DEMs have been proposed, including Map Algebra DEM (MADEM) (Hu et al., 2007a, 2007b) and High Accuracy Surface Modelling (HASM) (Yue et al., 2007). MADEM is a linear interpolation on a horizontal projection along the line of steepest descent. The method can fully utilize all sampled elevation data and therefore its accuracy exceeds that of traditional methods such as TIN, kriging, and inverse distance weighted (IDW) (Hu et al., 2007a). The HASM method constructs a DEM by using discrete points and contours based on the fundamental theorem of surfaces (SMTS) (Yue et al., 2007). The HASM method significantly increases DEM accuracy compared to traditional TIN methods (Chen and Yue, 2010; Yue et al., 2007). In addition, the HASM method can also be applied to real-time dynamic simulations (Yue, 2011).
Digital photogrammetry is another popular method of constructing DTMs. The photogrammetric method involves processing overlaid digital images to produce DTMs from orthophotographic maps (Zhang and Zhang, 1996). The specific process includes calculation of directed parameters, automatic aerial triangulation, epipolar image resampling, image matching, and final DTM production. The development of RS imagery has led to greater use of the digital photogrammetric method to produce DTMs because the RS data acquisition process is more efficient than traditional field survey methods. The VirtuoZo digital photogrammetry system, which was created by Chinese scholars, is famous worldwide (Zhang et al., 2000). Chinese scholars have also discussed the selection of features for image matching (Wang, 2005), quality controls for producing DTMs (Du, 2009; Long et al., 2011), and determining the resolution for expressing DTMs (Wang, 2013) during the DTM construction process.

2.2 High fidelity-based digital terrain modelling

Among traditional vector- and raster-based DTM types, regular grid-, contour- and TIN-based DTMs are often used in geological research. These models meet the basic requirements of geo-applications in expressing surface morphology. However, many geographical objects have complicated surface morphologies. One example is a complex landscape that includes both areas of gradual and rapid topographic change. While vector-contour DTMs can only provide general information about topography, the vector TIN method can describe areas with gradual and rapid changes. However, the TIN data structure and calculations process are complex and cannot be accurately extended over large areas. Interpolated regular-grid DEMs are restricted by the similarity presupposition of the First Law of Geography. That is, interpolated DEMs are more suitable for expressing surfaces characterized by gradual change, and areas with sudden changes in relief (including specific geomorphological features) are often ignored. Photogrammetric regular-grid DEMs are constructed from overlaid orthophotographic images, and many types of surface information cannot be acquired by orthophotographic cameras. In addition, photogrammetric DEMs often do not reproduce geomorphological features such as ridge lines and gully networks, even though these features are sampled during the image-matching process used to produce the DTM. To compensate for this issue, algorithms should be proposed to extract geomorphological features from photogrammetric DTMs during the digital terrain analysis process.
2.2.1 Point-by-point high fidelity modelling based on TINs
The problems with the traditional DTM types described above demonstrate that current DTM data models cannot meet the need for high-fidelity terrain modelling and terrain analysis. Instead, high-accuracy applications in complex areas require a high-fidelity-based digital terrain modelling method. To resolve the inability of regular-grid DTMs to express terrain features, many Chinese scholars have developed high-fidelity DTMs using the TIN method, which includes all points and topographical features. Such DTMs include feature-preserved DTMs (FP-DTM, Wang et al., 2009), plain river network area-oriented DTMs (Gao, 2010), and terraced DTMs (Zhu et al., 2011; Zhao et al., 2013). These hybrid DTMs combine or overlay high-accuracy vector DTM data with grid DTM data, resulting in higher fidelity terrain expression. Similarly, a unified raster- and vector-based digital terrain modelling method has been developed, retaining the advantages of both raster and vector data structures and preserving the terrain features (Gong, 1992). This concept has been explored using different data structures (Chang and Liu, 1998; Wang and Teng, 2010). However, due to its complex data structure, more development is needed before this novel DTM data model can be applied in practice.
2.2.2 Point-by-point high-fidelity modelling based on point cloud
LIDAR point clouds are another data source for high-fidelity digital terrain modelling. These point clouds, which represent a surface, are acquired using an on-board, truck- mounted, or ground-based laser scanner. The points are then connected to construct high-fidelity DTMs using approaches such as propinquity rules (Cheng et al., 2013; Wang and Guo, 2012; Wang and Hu, 2012; Zhang et al., 2009). The resulting DTMs have highly detailed geometric structures due to the high density of points in the LIDAR point cloud.
With the development of photogrammetry, new photogrammetric methods for constructing high-fidelity DTMs have become available in China. These include oblique photogrammetry, close-range photogrammetry, and LIDAR point clouds measured by 3-D laser scanners. Oblique photogrammetry, which differs from vertical aerial photogrammetry, is an oblique photographic technology in which images are acquired with multiple digital cameras on a single platform. These cameras are placed at specific angles with respect to the ground. These images acquired at different angles allow for the construction of DTMs and other geographical products by matching images from various view directions (Tian et al., 2013; Zhang et al., 2017). Oblique photographic technology avoids common vertical aerial photographic problems such as blind angles and covered objects. Thus, this technology could play a valuable role in constructing high-fidelity DTMs as well as other GIS products for environmental monitoring (Li et al., 2015).
The popularity of digital cameras has made close-range photogrammetry another research focus in photogrammetry and computer vision (Zhang and Zhang, 2005). This method involves acquiring images or video from cameras with different viewpoints using either intrinsic parameter calibration or non-calibration. In the intrinsic parameter calibration method, density surface points are identified and polygon feature-based image matching is used to construct high-fidelity DTMs (Jia and Li, 2014; Ke et al., 2009; Zheng and Zhou, 2012). In the non-calibration method, feature extraction is performed first, followed by image-matching; finally, the structure from motion (SFM) method is used to capture points and construct high-fidelity DTMs (Jiang et al., 2008; Ling et al., 2012; Xiao et al., 2009).

2.3 Real-time dynamic geographical scene modelling

Real-time dynamic geographical scene modelling is generally thought to be distinct from geomorphometry in GIS. However, the terrain surface, which forms part of a geographical scene, can also be constructed when modelling the geographical scene. Thus, real-time dynamic geographical scene modelling can use the photogrammetric methods described above (see section 2.2) to digitally construct geographical scenes after surveying or taking multiple videos of a scene.
Various models, including geometrical models, image models, voxel models and point cloud models, have been used to express a geographical scene using the photogrammetric method of multiple surveying. However, the geographical scenes expressed by these models are always static and can therefore only be used to obtain simple geometrical measurements (Chen et al., 2015; Li et al., 2014; Liao et al., 2014; Zhang et al., 2015). Therefore, video-based real-time dynamic geographical scene modelling is being pursued by Chinese scholars.
Recent achievements in video-based real-time dynamic geographical scene modelling include 3D self-adapted scene construction using videos, the geographical positional method of constructing 3D scenes from videos, feature extraction and modelling of targets in videos, and integration and expression of multiple geographical data and video 3D geographical scenes (Dong et al., 2014; Hu et al., 2014; Liang et al., 2013; Liu et al., 2014; Wang et al., 2014; Zhen et al., 2014). In addition, portable devices, such as mobile phones, are being used to update local geographical scenes. These achievements represent a unique research direction both in real-time dynamic geographical scene modelling and in real-time dynamic terrain modelling of geomorphometry.

3 Methods of digital terrain analysis

3.1 Extraction of terrain derivatives

Terrain derivatives (also called terrain factors) are parameters or indices with specific geographical meanings that can be used to investigate surface morphology characteristics. The extraction of terrain derivatives is a core research focus of DTA. Algorithms for various hillslope-based terrain derivatives have been developed using DEMs and are now being refined. In addition to traditional hillslope-based terrain derivatives (slope, aspect, plan curvature, profile curvature, slope length, terrain roughness, terrain relief, elevation variation coefficient, and terrain cut depth) (Yang et al., 2009), Chinese scholars have proposed new terrain derivatives and algorithms based on local geographic characteristics and their specific research needs. These include the terrain information content (Dong and Tang, 2012; Tao et al., 2010), terrain complexity index (Wang et al., 2004), terrain driving force (Li and Tang, 2006), potential factor for water erosion (Liu et al., 2012), erosional slope length and regional slope length factor (Zhang et al., 2012; Zhang et al., 2013), and others. These results significantly enrich the usefulness of terrain derivatives.
Because so many terrain derivatives have been proposed, various authors have classified all terrain derivatives into several main types (Tang et al., 2005; Zhang, 2013; Zhou and Liu 2006). For instance, Zhang (2013) categorized terrain derivatives according to their application, calculation methods and scale characteristics. This work provided an important basis for improving analytical efficiency and applying terrain derivatives. In addition, the algorithms used for terrain derivatives, including algorithms for slope, slope aspect, terrain roughness and terrain relief, have been refined by many Chinese scholars (Chen et al., 2008; Lang et al., 2007; Tao and Tang, 2011; Xie et al., 2013; Zhao et al., 2012). Suitable window size and the optimal scale for extracting slope have also been discussed (Liu et al., 2009; Zhao et al., 2012).
The terrain derivatives discussed above can express terrain characteristics for a pixel and even a local area, and these characteristics can then be used to determine large-scale patterns and landform spatial structures. However, these pixel-based terrain derivatives have significant limitations with regard to analysing the characteristics of large-scale landforms. Therefore, Chinese scholars have developed several new methods to describe large-scale landforms. For instance, the slope spectrum method (Tang et al., 2008) uses a second-order terrain derivative that reflects the characteristic slope in a specific area. Similarly, the catchment profile spectrum (Zhang, 2011) and the hypsometric integral spectrum (Zhu et al., 2013) were developed to investigate large-scale landforms on the Loess Plateau of China. Other studies have focused on terrain texture and slope-landscape structure to better understand how landform morphology variations are generated (Liu et al., 2012; Sun, 2011; Zhao, 2012).

3.2 Extraction of geomorphological features

Geomorphological features are specific features (geomorphological points, lines and polygons such as peaks, saddles, ridges, and gullies) on the land surface that can help recognize and classify landform types. These features control the spatial geomorphology of an area and are therefore important components of surface morphology.
Chinese scholars have proposed several methods of extracting geomorphological points from DEMs. Some examples are the extraction of surface peaks from reverse DEMs (Zhong et al., 2009), the extraction of stream runoff nodes (Yi et al., 2003), and the extraction of saddles based on runoff concentration simulations or extreme elevation points along watershed boundaries (Kong et al., 2013; Xiong et al., 2013; Zhang et al., 2011). Gully knickpoints can be extracted using the energy accumulation and the gully profile (Bi et al., 2011; Liu et al., 2013), and this information can be used to infer gully formation processes and related tectonic activity (Sun et al., 2012; Zhang et al., 2012). Gully head points have also been extracted based on geomorphological structures (Jiang et al., 2014). In addition, Luo (2008) proposed the concept of terrain feature point clusters, which can be determined from the spatial relationships between geomorphological points. These point clusters can be used to classify landforms based on the organization of peaks, stream runoff nodes and saddles. Peak clusters were also used to identify upland planation surfaces (Xiong et al., 2017a) Chinese scholars have also made significant progress in methods for the extraction and analysis of geomorphological line features. Ridge and gully lines are the most typical line features and represent major terrain structures; thus, methods for their extraction have received much attention. These methods can be divided into data source-based and algorithm principle-based methods. In the former, the data sources used for ridge and gully line extraction include contour maps (Jin et al., 2006; Zhang et al., 2013), TIN (Ai et al., 2003), grid DEMs (Chen and Liu, 2001; Kong et al., 2012; Zhou et al., 2007) and LIDAR point clouds (Li et al., 2013). In the latter, the algorithms include flow direction-based methods, image-based methods, surface morphological structure-based methods, or a combination of surface morphological structure and flow direction methods (Huang, 2001; Luo, 2008; Zhou et al., 2007).
The extraction and analysis of geomorphological line features are also a focus of research regarding the Loess Plateau of China and especially the area’s loess shoulder line. The loess shoulder line is considered an important geomorphological boundary for classifying loess landform units and representing loess landform morphological characteristics (Xiong et al., 2014c). Therefore, methods for extracting the loess shoulder line are a major research focus in DTA of the plateau. To improve the accuracy and efficiency of loess shoulder line extraction, Chinese scholars have proposed a series of methods for extraction of the loess shoulder line, including methods based on slope variation (Zhu et al., 2003), flow path characteristics (Liu et al., 2006), morphological structure (Lu et al., 1998), LOG edge detection (Yan et al., 2011) and a snake model (Song et al., 2013; Zhou et al., 2013).
In recent years, many Chinese scholars have investigated geomorphological polygon feature extraction. Research achievements in this area have mainly centred on positive and negative terrain extraction in loess landforms (Chen et al., 2012; Zhou et al., 2010a; Zhou et al., 2010b), upland planation surfaces extraction on the Tibetan Plateau (Xiong et al., 2017a), and fenglin and fengcong landform extraction in karst landforms (Huang et al., 2014; Liang and Xu, 2014; Xue et al., 2009). In addition, object-based image analysis (OBIA) methods have been used to classify geomorphological polygon features, leading to a new area of landform classification research (Zhao et al., 2017).

3.3 Watershed hydrology-based DTA

Watershed hydrology is a key issue in both geomorphometry and geography. Surface morphology profoundly affects water flow generation and routing in watershed hydrology. In addition, differences in terrain features can lead to spatial differences in hydrological characteristics. The topological relationships and geometrical shapes of terrain features directly influence the properties of a watershed (Ren and Liu, 2000). Chinese scholars have mainly addressed two aspects of watershed hydrology-based DTA, static analysis of hydrological characteristics and dynamic modelling of hydrological processes. The former aspect addresses hydrologically correct DEMs (Yang et al., 2007), methods of processing DEM data from flat areas and depressions (Xie et al., 2005; Xu et al., 2007), the design of flow model and flow routing algorithms (Chen et al., 2014; Qin et al., 2007; Xiong et al., 2014c; Zhou et al., 2011), and the extraction of hydrological feature objects (Yi et al., 2003; Zhu et al., 2012). The latter aspect concerns methods of constructing distributed hydrological models (Wang et al., 2002), the effects of DEM scale on hydrological models (Gao and Jin, 2012), and how different watershed delineation strategies influence the simulation of hydrological processes (Qiu et al., 2012; Zhang et al., 2004). A specific research direction in watershed terrain analysis concerns the delineation of watersheds by DEMs and the detailed terrain characteristics of watersheds. This research direction takes the watershed as a basic statistical unit and strives to create a hierarchical structure pattern of topographical, geomorphological and hydrological features at different watershed scales with the goal of characterizing geographical and hydrological processes in a reasonable way (Xiong et al., 2016a).
In recent years, a series of hydrological models have been introduced based on GIS and geomorphometry (Guo et al., 2000; Li et al., 2009; Li et al., 2011; Ren and Liu, 2000; Wang et al., 2002; Zhang et al., 2004). These models aim to dynamically simulate hydrological processes in different areas and on different scales (Liu et al., 2003; Wan et al., 2010; Wang et al., 2008). Because terrain analysis is closely related to hydrological modelling, investigating the role of terrain analysis in hydrological modelling could help use terrain factors to support the development of hydrological models and expand the applications of terrain analysis methods to hydrology.

3.4 Strata structure-based DTA

As geospatial simulation science advanced, research in geomorphometry has expanded to include terrain modelling and analysis of underlying strata. The investigation of underlying strata gradually came to represent a specific research direction in geomorphometry. Currently, strata structure-based DTA includes modelling of the underlying strata and terrain analysis of the strata. Chinese scholars have used a variety of 3D geological modelling methods to model the underlying strata (Li et al., 2013). These methods can be divided into data source-based methods and spatial simulation function-based methods. Data source-based methods reconstruct the underlying strata using information from drilling (Liu et al., 2009; Lin et al., 2013; Wu et al., 2007; Zhu et al., 2004), geological profiles (Cheng et al., 2007; Guo et al., 2009; Ma and Guo, 2007; Ming et al., 2008; Wang et al., 2003; Zhou et al., 2013), seismic data (Ma et al., 2003; Xiong et al., 2016b; Zhao and Lin, 2010), or the integration of multiple data sources (Wu et al., 2005; Zhong et al., 2007; Zhou et al., 2007). In contrast, reconstruction of underlying strata using spatial simulation functions involves surface simulation with discrete or incomplete data using some mathematical function, such as linear TIN, IDW, spline, natural neighbour interpolation, or kriging. All these functions can be used to simulate the strata, which are then analysed to understand landform evolution processes.
Using reconstructed strata, Chinese scholars have also conducted terrain analysis of the strata themselves and the relationship between the strata and the modern surface (Cheng et al., 2010; Xiong et al., 2014a, 2014b). For instance, the landform inheritance characteristics of loess areas was explored by comparing reconstructed strata underlying the loess to the current loess landforms (Xiong et al., 2014a). In addition, two terrain derivatives, the terrain-relief change index (TRCI) and the bedrock terrain controllability index (BTCI) were proposed to explain the spatial variation of loess deposition landform evolution and loess gully formation (Xiong et al., 2016a; Xiong et al., 2017b).

3.5 Ocean dynamics-based DTA

The surface of the ocean offers another interesting surface morphology that can be geomorphometrically constructed using satellites. In previous research, the ocean surface has generally been described based on its mean elevation. However, the ocean surface has morpho- logical characters, which is determined by mean wave length, height, period, speed, and direction (Song et al., 1998; Zhang et al., 2010).
Waves can be short or long, and their length is influenced by ocean dynamics. Normal ocean waves are short waves with high frequencies, and can be caused randomly by wind, storms, and tsunamis (Kong et al., 2008; Liu et al., 2005; Ye et al., 2013; Zhao et al., 2010). While these events always produce short waves, the waves may differ in height, periodicity, speed and direction. Because the surfaces of short waves change rapidly and randomly, the surface morphology of the ocean is not easy to measure in real time. In contrast to short waves, long waves are determinated waves are with low frequencies and they are caused by celestial bodies motion. In particular, an astronomical tide refers to the specific ocean surface morphology caused by tide-generating forces exerted by the sun and moon on the terrestrial ocean. Generally, ocean surface morphologies associated with high or low tide level appear within a certain time period, and this time period can be inferred from the relative positions of the earth, moon, and sun. In addition, the ocean surface morphological features caused by astronomical tides can be modelled and forecasted in real time by harmonic analysis method.
In recent years, spatial variations in the ocean’s surface along the northwest Pacific margin have been explored using satellite altimetry and tide level data (Jia et al., 2000; Lin et al., 1997; Wang et al., 2008; Yu et al., 2008). In addition, mean sea level variability related to the El Niño-Southern Oscillation (ENSO) have been analysed to understand ENSO’s effects on regional to global ocean surface morphology (Yuan et al., 2009). These studies have contributed to monitoring regional to global changes in ocean surface morphology. In addition, the high accuracy and resolution of satellite altimetry data greatly facilitate research on the spatiotemporal patterns and evolutionary processes associated with changes in ocean surface morphology.

3.6 Socioeconomic spatial structure-based DTA

Geomorphometry is often used in the natural sciences but is generally considered to have little relationship to the social sciences. However, if a DTM is conceptualized as a field model and its elevation attribute generalized, it can be used to express the spatial structure of any social phenomenon. Thus, geomorphometry can also be used in social science. This section uses the social factor of accessibility as an example and then demonstrates the feasibility of socioeconomic spatial structure-based DTA.
The index of accessibility refers to the level of difficulty of accessing one area from another area; thus, it reflects the spatial difficulties that people need to overcome during travel (Li and Lu, 2005; Jiang et al., 2013). Accessibility is quantitatively expressed in terms of distance, time and cost. The analysis of accessibility is gradually becoming a reference for the reasonable arrangement of urban public service facilities. Using geomorphometry, the distance, time and cost factors of accessibility constitute the attributes of a field model that can be used in further analysis (Pan and Liu, 2014). For instance, several studies have described accessibility using a field model and explored changes in accessibility using the weighted least distance calculated by Bayesian neural network algorithms (Liao et al., 2015; Ma and Cao, 2008; Shang et al., 2014; Zhang and Lu, 2013).
The spatial analysis of accessibility can be categorized based on whether it uses vector or raster data (Jin et al., 2010; Meng et al., 2014). Vector data-based accessibility analysis integrates the true conditions of a road network, including detailed parameters such as road speed, road conditions and turnaround in all directions. However, acquiring vector data is complicated and requires high accuracy and precision (Liu et al., 2010; Sun et al., 2012). In contrast, raster-based accessibility analysis divides an entire area into raster cells. Each cell represents various accessibility attributes in different layers, so the full accessibility characteristics of an area can be described by stacking the layers. However, these characteristics do not include the degree of connectedness between cells in an area (Chen et al., 2015; Shen et al., 2012). Together, these issues form a new research direction concerning the socioeconomic spatial structure of accessibility-based DTA (Chen et al., 2009; Zhu et al., 2011).

4 Applications of geomorphometry

The theory and methods of geomorphometry have provided new approaches and technologies that can be used in traditional geographical studies. In recent years, Chinese scholars have applied geomorphometry to a wide variety of topics in geoscience, including global climate change, the Taihu Lake Plain, the Loess Plateau, the Tibetan Plateau, and the lunar surface.

4.1 Global topography and climate change

The morphology of the Earth has been regarded as the result of internal and external forces and Earth dynamics. The internal forces provide the basis for the surface morphology formation of Earth, while the external forces create the details of the Earth’s surface morphology. In terms of the global-scale surface morphology, the interactions of different ‘plates’ are the main internal forces that shape the macroscale topography of Earth. Notably, such processes include plate subduction and extrusion (Zhou, 2013; Zhang et al., 2017). However, the topography itself also affects the process of globe climate change. Terrain derivatives such as slope, aspect, and elevation greatly affect variations in surface solar radiation, which further influences the spatiotemporal distribution of climate factors. Therefore, Chinese scholars have applied geomorphometry to the field of climate change. These studies fall into two main categories. First, some applications involve using DEMs to create models capable of estimating climate factors. For instance, studies have described a distributed model for calculating astronomical radiation using a DEM (Zeng et al., 2005), as well as a model for total radiation (Hao et al., 2009; Yang et al., 2004). Other scholars have used geomorphometry to model rainfall-runoff (Wu et al., 2002), simulate land surface evapotranspiration (Liu et al., 2007), model temperature fields in mountainous areas (Mo and Zhang, 2007), and air pollution (Zhang et al., 2014a, 2014b, 2016). Second, some applications involve the use of DEMs to develop interpolation methods for climate factors. These include spatial interpolation methods for precipitation (Liu et al., 2010) and surface air temperature (Pan et al., 2004; Yang et al., 2007). In addition, on a global scale, spatial variations related to ENSO have been linked to changes in ocean surface morphology (Yuan et al., 2009).

4.2 Taihu Lake Plain

In addition to the application of geomorphometry in mountainous areas, another interesting application area of geomorphometry is associated with the Taihu Lake Plain in the low reach of the Yangtze River. This plain area contains many interconnected river networks, lakes, reservoirs, and polder areas. The polder areas are man-made geographical features that were created to protect against the floods that frequently occur in this part of southern China. The polder areas change water flow routing, which increases the complexity of watershed hydrological processes in the plain area (Gao and Han, 1999; Mo, 2001). Three methods have been used to deal characterize the polder areas in this region. First, the traditional workflow for mountainous areas was used to simulate watershed hydrology and the characteristics of polder areas were ignored (Huang et al., 2011; Lai and Yu, 2007). Specifically, the polder areas were automatically classified into a specific subwatershed. Second, the polder areas were regarded as independent watersheds, and their hydrological processes were simulated (Luo et al., 2013; Xu and Wang, 2010). Third, the Soil and Water Assessment Tool (SWAT) was used to simulate the hydrological processes in polder areas based on the relationship between polder areas and the neighbouring watershed units (Li et al., 2013; Wang, 2006) Although Chinese scholars have made many advances in watershed hydrological modelling in polder areas, a distributed hydrological model that accurately describes the interactions between human and natural effects in polder areas is still needed in future watershed hydrology-based digital terrain analysis.

4.3 Loess Plateau

Geomorphometric research on the Loess Plateau of China has focused on the spatial variability and the evolutionary processes of loess landforms. For example, a second-order terrain derivative, the slope spectrum, has been used to explore spatial variations in loess landforms on the plateau (Tang et al., 2008). Other scholars have incorporated terrain derivatives into studies of loess landform morphology and spatial variability, including the core topographical factor (Zhang et al., 2013), hypsometric integral (Zhu et al., 2013), terrain texture (Liu et al., 2012), positive and negative terrain (Zhou et al., 2010), and catchment profile spectrum (Zhang, 2011). Chinese scholars have also studied the formation and evolutionary mechanisms of loess landforms on both watershed and regional scales. On the watershed scale, Fu et al. (1994) and Wang et al. (2007) investigated landscape loess morphology and soil erosion mechanisms. A cellular automata (CA) model was also used to simulate the evolution of positive and negative terrain in loess landforms using DEM data from different time series (Cao et al., 2013; Zhang et al., 2012). On a regional scale, landform evolution modelling and paleotopographic reconstruction was used to discuss landform inheritance characteristics (Xiong et al., 2014a, 2014b).

4.4 Tibetan Plateau

There are three major ways that scholars have applied geomorphometry to Tibetan Plateau research: terrain visualization, extraction and analysis of terrain derivatives, and integration of multidisciplinary data for the plateau. In the first case, Liu et al. (1999) reconstructed the DEM of the planation surface in the northeastern part of the plateau, which aided in visualization of the specific planation surface for geological investigation. Second, the relationship between plateau topography and uplift processes were explored using terrain derivatives extracted from DEMs and geological profiles (Han et al., 2012; Xiong et al., 2017a; Zhao et al., 2009). Landform divisions on the plateau were also classified using extracted terrain derivatives (Yao et al., 2007). Finally, the availability of RS images and DEMs has meant that integration of these data in the fields of geology, sedimentology, tectonics, and geomorphology has a major focus in studies of the Tibetan Plateau. These studies include drainage system analysis (Li et al., 2012; Zhang et al., 2006), tectonic active structure analysis (Ji et al., 2011), paleosurface reconstruction (Gao and Liu, 2013), and periglacial geomorphology monitoring (Zhao et al., 2007).

4.5 Lunar surface

As space exploration technology has advanced, geomorphometry has also been applied to morphological investigation of the lunar surface. Using data from the lunar orbiter of the Chang’e satellite, Chinese scholars have constructed a 500-m resolution DEM of the entire Moon, as well as a partial geomorphological map (Chen et al., 2012; Chen et al., 2013; Ding et al., 2012; Li et al., 2010). Because lunar craters are the basic unit of the lunar surface, lunar morphology research focuses on lunar craters. Using lunar DEMs, Chinese scholars have extracted lunar craters and analysed their features. These works include DEM-based exploration of the distribution of the Moon’s gravitational field (Huang et al., 2009) and various methods for extracting lunar craters, such as an object-oriented method and a mathematical morphological approach (Yuan et al., 2013; Yue et al., 2008). In addition, extracted craters have also been used to analyse lunar crater morphology (He et al., 2012; Yue et al., 2012; Zhou et al., 2012), and the spatial distribution of lunar landforms has been examined (Zhou et al., 2011).

4.6 Other applications

Geological disasters such as earthquakes, landslides, and collapses are closely related to topography. DEMs are a key data source for the application of geomorphometry to the analysis of geological disasters (Cui, 2014). For example, Chinese scholars have applied geomorphometry to landslide susceptibility mapping (Zhu et al., 2014) and used analysis of terrain derivatives to investigate landslide triggering factors (Bai et al., 2005; Lan et al., 2002).
The application of geomorphometry to soil science has mainly centred on soil sampling, soil erosion and the investigation of soil attributes. In the area of soil sampling, DEMs are used to inform sampling strategy design and soil mapping (Yang et al., 2011), while soil attribute investigations have used DEMs to investigate the topographic wetness index (TWI) (Qin et al., 2006; Zhang et al., 2006). Other studies have explored the relationship between soil erosion and topography and assessed soil erosion in a large-scale watershed (Fu et al., 2005). In addition, regional-scale soil erosion modelling has been conducted using terrain derivatives (Liu et al., 2004; Yang et al., 2006; Yang et al., 2009), and this type of modelling has also been used to analyse the variability in regional-scale soil erosion (Bi et al., 2013; Guo et al., 2009).
In addition to the applications of geomorphometry in traditional domains, Chinese scholars have also applied geomorphometry in several novel areas, including specific terrain rendering of maps, remote sensing, and human geography. In addition to traditional terrain-rendering methods such as level of detail (LOD), elevation classification and rendering, and hill shading, the development of computer graphics has led to new methods for rendering surfaces, such as painting rendering from DEMs (Chen, 2011). In addition, the combination of geomorphometry and remote sensing has been used to guide agricultural production and the assessment of natural resources with high accuracy and high renewal frequency (Long et al., 2007; Wang et al., 2010). Finally, geomorphometry has been applied to studies of the spatial distribution and planning of urban man-made buildings (He et al., 2012; Zhang et al., 2011).

5 Conclusion

Because topography and geomorphology are basic research topics in geography, geomorphometric research is an important component of GIS. Since the development of geomorphometry nearly half a century ago, significant progress has been made in the related theory, methodology and applications. Chinese research in geomorphometry in China has proceeded along with international studies. This paper’s review describes the recent advances in geomorphometry in China. Many high-impact and internationally significant achievements have been made by Chinese scholars, especially in the fields of high fidelity-based digital terrain modelling, extraction of geomorphological features, and strata structure-based DTA, as well as in the geomorphometry of the Loess and Tibetan Plateaus. In 2006 and 2013, two international conferences on geomorphometry occurred at Nanjing Normal University of China, Geomorphometry 2006 (TADTM, Terrain Analysis and Digital Terrain Modelling) and Geomorphometry 2013 (see http://geomorphometry.org/); these conferences demonstrate the international respect earned by the Chinese scholars.
As DEM data acquisition methods progress, the acquisition of high-resolution DEM data should become more efficient and convenient. There are significant opportunities in geomorphometry for Chinese scholars. First, future Chinese research on geomorphometry should emphasize the concept of geoscience attributes. These attributes should include elevation, and other geospatially related information, such as underlying strata, ocean surface characteristics, and social phenomena. In addition, exploration of the theory and methods of geomorphometry should continue, and research directions should be expanded. For instance, studies should shift their focus from the geomorphometry of traditional mountainous areas to that of areas of plain river networks or submarine topography, and from the spatial variability of modern surface morphology to process- and mechanism-based landform evolutionary modelling. In particular, geomorphometric research ideas and methods could be expanded to other field models in geoscience, and a universal field model in geoscience with its own theory and method could be proposed and developed.

The authors have declared that no competing interests exist.

References

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[2]
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Chen J L, Wu W, Liu H B, 2008. Effect of DEM interpolation on the slope and aspect.Research of Soil and Water Conservation, 15(6): 14-17. (in Chinese)In many cases of the research and application,digital elevation data may be the only source for DEM generation with algorithms,which are available or affordable.It is known that the analytic result from the DEM can vary in quality depending on their algorithms.Taking hilly region in southern China as research region,using the digital contour with the scale of 1∶10 000 as the source,this paper compared the slope,aspect from the DEM generated with five algorithms,the results showed that there were significant effect on the slope among the algorithms when the slope 30°,but there were no significant effect on the slope among the algorithms and resolution when the slope 30°.Furthermore,the result also showed that DEM interpolated with ANUDEM is the most precise,however,there was no flat area in the result from the terrain analysis in the region with extensive flat area,so it can't be suitable for performing terrain in such region.

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Chen M, Wen Y N, Yue S S, 2015. A progressive transmission strategy for GIS vector data under the precondition of pixel losslessness.Arabian Journal of Geosciences, 8(6): 3461-3475.It is well known that the final results of geographic information system (GIS) mapping are composed of rasterized pixels in most display devices. Based on this, pixel equivalence is proposed as two vector data that can produce the same raster image on a device under the same mapping processes and parameters. Moreover, if between the two data, one is considered the original data and the other is its reduced-quantity version, then the latter can be regarded as pixel losslessness relative to the former. In this case, the reduced-quantity version can be used instead of the original data to produce the same result from the perspective of visualization. The aim of this article is to explore how to produce the transmitted data, including an initial code and a series of increments that are used for progressive transmission, to retain pixel losslessness. By illustrating that the vector data can be represented by a vertex or ordered sequence of vertices, this article introduces the detailed concepts of pixel equivalence and pixel losslessness of vector data. Then, the requirements for pixel equivalence between two vertices are deduced by analyzing the coordinate transform processes under specific assumptions. The method to generate an initial code and a series of increments related to a single vertex is proposed to produce vertices that are pixel equivalence to the original vertex under different coordinate transform processes. By discussing the traversing mode of the ordered sequence of vertices based on quadtree cells, a coding algorithm is proposed to develop the progressive transmission related to the multi-vertex and to generate reduced-quantity versions to retain pixel losslessness. Finally, experiments are designed to demonstrate that, under the precondition of pixel losslessness, the proposed progressive transmission method can significantly reduce the amount of transmitted data in the network environment.

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[14]
Chen X, Li Q, Wang Y Jet al., 2009. The critical cluster model and its application in accessibility assessment of public bus network.Acta Geographica Sinica, 64(6): 693-700. (in Chinese)The Critical Cluster Model (CCM) is a network optimization model that can be used to identify neighborhoods facing transportation difficulties during an evacuation process. It defines the Bulk Lane Demand (BLD) as the ratio of population to exit capacity that is adversative to the meaning of accessibility. Based on this context, this paper applies CCM to assess the accessibility of public bus network by introducing multiple bus lines in the certain road sections and considering the spatial distribution of population being assigned to each bus stop. The bulk bus line demand, as the substitution of original BLD, is therefore used to reflect the people's convenience in taking public buses. An application of CCM in accessibility assessment of public bus network in Beijing tests the flexibility of this method. Considering the importance of accessibility in urban transportation, the modification of CCM by introducing other factors should be the focus of further studies.

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[15]
Chen Y G, Tang G A, Zhou Yet al., 2012. The positive and negative terrain of loess plateau extraction based on the multi-azimuth DEM shaded relief.Scientia Geographica Sinica, 32(1): 105-107. (in Chinese)Based on the DEM data of Jiuyuangou wateshed in Suide County,Shaanxi of China,with a spatial resolution of 5 m,employing the digital terrain analysis,multivariate statistics and data mining methods,multiple indexes of multi-azimuth DEM shaded relief and slope are established.The solutions of extraction positive and negative terrain of loess plateau by Principle Components Analysis,and Logistic regression model is proposed.The result indicates that: the extracting model has better consistency and accuracy,of which the accuracy is 82.1% and Kappa statistics is 0.6298.Tested on 6 samples of different valley by this model,the mean accuracy of positive and negative terrain are at 77.6% and 84.9%,and weighed mean accuracy is 81.3%.It is suitable to extract positive and negative terrain of loess plateau by PCA and Logistic regression model.

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[16]
Chen Y L, Liu D Y, 2001. A new method for automatic extraction of ridge and valley axes from DEM.Journal of Image and Graphics, 6(12): 1230-1234.In this paper, a new method for automatic extraction of ridge and valley axes from DEM, named as Directional Profile Approach(DPA), is proposed. DPA can automatically determine whether a grid point in DEM is a possible ridge(or valley) grid point, according to the features of the profiles through this grid point. Applying this new method to extracting ridge and valley axes automatically from DEM, the following several procedures must be accomplished: First, the all elevation grid points which may be located in ridge and valley lines are automatically recognized with DPA. Then the modified Hilditch thinning algorithm is applied to selecting the ridge and valley grid points recognized by DPA. Third, the every two neighboring ridge points or valley points are connected and rudimentary form of the ridge or valley axes is constructed. Finally, the closed triangles in ridge and valley axes are broken and the short branches are removed. A real DEM was used for testing data, the ridge and valley axes extracted automatically by this method can basically represent the topographic features of the corresponding topographical map. Therefore, this new method is effective.

[17]
Chen Y, Zhou Q, Li Set al., 2014. The simulation of surface flow dynamics using a flow-path network model.International Journal of Geographical Information Science, 28(11): 2242-2260.This paper proposes a flow-path network (FPN) model to simulate complex surface flow based on a drainage-constrained triangulated irregular network (TIN). The TIN was constructed using critical points and drainage lines extracted from a digital terrain surface. Runoff generated on the surface was simplified as ‘water volumes’ at constrained random points that were then used as the starting points of flow paths (i.e. flow source points). The flow-path for each ‘water volume’ was constructed by tracing the direction of flow from the flow source point over the TIN surface to the stream system and then to the outlet of the watershed. The FPN was represented by a set of topologically defined one-dimensional line segments and nodes. Hydrologic variables, such as flow velocity and volume, were computed and integrated into the FPN to support dynamic surface flow simulation. A hypothetical rainfall event simulation on a hilly landscape showed that the FPN model was able to simulate the dynamics of surface flow over time. A real-world catchment test demonstrated that flow rates predicted by the FPN model agreed well with field observations. Overall, the FPN model proposed in this study provides a vector-based modeling framework for simulating surface flow dynamics. Further studies are required to enhance the simulations of individual hydrologic processes such as flow generation and overland and channel flows, which were much simplified in this study.

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[19]
Cheng D, Yang Q, Zhang Y Bet al., 2007. Three-dimensional geological modeling based on hydro sections.Journal of Beijing University of Aeronautics and Astronautics, 33(11): 1362-1366. (in Chinese)Since section is a common and valuable data model,a novel modeling method based on sections was proposed,namely "section information extraction",and modeling steps were presented.The matter to which attention should be paid and necessary preprocessing before modeling based on sections were analyzed.Methods of section generalization,section mapping from the space of two-dimension to that of three-dimension,building background grid of section information and correcting error section information were introduced.A novel method of "top surfacepinch out line-lens" was applied to reconstructing lens model,which converted the complex multiple-valued modeling to single-valued modeling.Then modeling algorithms of single-valued layer and lens were described respectively.At last,an application example was shown,which proved the efficiency of the modeling method based on hydro geological sections.

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[20]
Cheng L, Tong L H, Li M Cet al., 2013. Semi-automatic registration of airborne and terrestrial laser scanning data using building corner matching with boundaries as reliability check.Remote Sensing, 5(12): 6260-6283. (in Chinese)Data registration is a prerequisite for the integration of multi-platform laser scanning in various applications. A new approach is proposed for the semi-automatic registration of airborne and terrestrial laser scanning data with buildings without eaves. Firstly, an automatic calculation procedure for thresholds in density of projected points (DoPP) method is introduced to extract boundary segments from terrestrial laser scanning data. A new algorithm, using a self-extending procedure, is developed to recover the extracted boundary segments, which then intersect to form the corners of buildings. The building corners extracted from airborne and terrestrial laser scanning are reliably matched through an automatic iterative process in which boundaries from two datasets are compared for the reliability check. The experimental results illustrate that the proposed approach provides both high reliability and high geometric accuracy (average error of 0.44 m/0.15 m in horizontal/vertical direction for corresponding building corners) for the final registration of airborne laser scanning (ALS) and tripod mounted terrestrial laser scanning (TLS) data.

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[21]
Cheng Y P, Shi J S, Yang Z Jet al., 2010. Control of ancient landform on rock-soil erosion in loess area.Arid Land Geography, 33(3): 334-339. (in Chinese)The soil erosion in the loess area of China is very serious.To study the developing tendency of rock-soil erosion in the loess area helps the control and treatment.The digital model of ancient landform in Jurassic and Tertiary in a small river basin in Fugu County of Shaanxi Province,China,has been established with the application of the high-precision GPS,RS and GIS.The elevation of the top of Jurassic and Tertiary strata as well as the elevation of modern landform has been measured with the grid density of 1 000 m 1 000 m,the analysis and comparison have been made for the soil erosion evolution with the remote sensing images processed by the TM satellite data.It has been found that the loess area in Fugu County has gone through three geomorphologic developing processes,namely,ancient peneplane-ancient lake lowland-plateau gully.Each geomorphologic process developed based on the previous geomorphologic process.The rising of Jurassic strata led to the missing of Cretaceous strata.In the late Cretaceous,the Jurassic strata in the study area were submerged with lake water because of the tectonic movement.The Tertiary deposited with a considerable thickness and the sediments were lacustrine.However,the Tertiary argillaceous sediments were not in the same lacustrine environment,they deposited in the lowest ancient land and gradually upwards in the formation process of mudstone sedimentation,which can be verified by the densely-developed,lateral,continuously-distributed calcareous concrete beds.After the Tertiary sedimentation,the large faults occurred in the late Tertiary Himalaya movement.Some faults followed the faults in the late Yanshan movement and the basalt eruption occurred before the laterite accumulation.The graben of the Yellow River was formed by the influence of the Himalaya movement.Influenced by the tectonic movement,the whole area rose to form the smooth ground surface,which was composed of purplish-red mudstone with densely-developed Tertiary calcareous concrete beds.The deposit thickness was uneven,the maximum occurred in the lowest ancient land and the minimum occurred in the highest land.Due to the influence of the tectonic movement,the relatively "smooth land" was changed,the easily-changed section should be "tectonic fragile belt".It would consequentially change the overlying Tertiary mudstone,which was most influenced by the tectonic movement and the weathering of the mudstone was relatively high,so it was easily eroded to form small striae-small gullies-big gullies,resulting in the change of the level ground surface.The rock-soil erosion occurred because of various external forces,the Tertiary mudstone was also denuded.The mudstone in the gradually-formed landform was almost eroded out and washed away by the water flow because of large water catchment and strong water hydrodynamics,while part of mudstone remained in the relatively-high land because of the poor hydrodynamics and low rock-soil erosion.That was why the mudstone was rarely seen in the low land and easily seen in the high land.It was found from the results that the modern landform in the river basin had high inheritance of Jurassic and Tertiary erosion surface.Therefore,the ancient landform had important control on the rock-soil erosion in the loess area of northern Shaanxi area.The study results could provide the solid basis for the water-and-soil conservation.

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[22]
Cui P, 2014. Progress and prospects in research on mountain hazards in China.Progress in Geography, 33(2): 145-152. (in Chinese)In this paper, first, the research progress on fundamental theories on mountain hazards and prevention techniques are briefly reviewed. In the current research, the distribution of mountain hazards has been recognized and the hazards assessment methods for mountain torrents, debris flow and landslides have been established, and the principles and calculations of landslide stability analysis have been developed. In addition, the stress-strain relation of debris flow slurry and the formulae of velocity, discharge and impact of debris flow have been established, and a model of viscous debris flow initiation has also been proposed. We also presented the magnitude amplification effects of mountain torrents and debris flows. Meanwhile, the methods to forecast mountain hazards have been developed by analyzing both rainfall and ground factors. Based on the understanding of the physical characteristics of mountain hazards, a number of monitoring instruments have been invented, and especially the early warning methods have been used in the underdeveloped regions. Furthermore, a systematic technology for coping with mountain hazards has been developed. The topics on the formation, development, forecasting and prevention, protection strategies and risk management of mountain hazards have been proposed for future research. Finally, aiming at the requirements of the reduction of disasters for the nation and the goals of the academic progresses, we propose the topics that are worthy of more attention in the future research, such as the response of mountain hazards to ecology, the effects of climate change on mountain hazards, the prediction of catastrophe, the mesomechanic behaviors of the soil affected by water, the theories and methods of hazard risk assessment, the hazard forecasting model based on the formation mechanisms and the improvement of prediction and recovery technology.

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[23]
Ding X Z, Han k Y, Han T Let al., 2012. Compilation of the geological map of Sinus Iridum Quadrangle of the Moon (LQ-4).Earth Science Frontiers, 19(6): 15-27. (in Chinese)Based on CCD images,interference imaging spectral data and DEM data of China's lunar exploration project(Chang'e-I) and related processed and analytic results,an integrated study of regional geology of Sinus Iridum and Mare Imbrium was conducted,and a series of relevant researches and analyses were carried out,including analysis of impact craters and their extrusive and accumulative materials,division of stratigraphic and tectonic units and classification of rock types,integrated analysis of chronology and lunar evolution history.In consideration of crater's shape features,quantity and preserving status of filling materials,the lunar impact craters can be divided into 7 types and 11 sub-types,and the accumulative materials of craters are divided into 6 types and 9 accumulative groups.According to the content and distribution of TiO2 and image characteristics,the basalts are divided into high-TiO2,medium-TiO2 and low-TiO2 basalts.Discussion was made on division of tectonic units and evolution features in the study area.The geological map of the Sinus Iridum Quadrangle(LQ-4) at a scale of 1 2.5M was preliminarily compiled with the ArcGIS system,and the spatial database of the map was established.Related technical specification,procedure and method for lunar geological mapping have been worked out,so as to lay a foundation for the forthcoming geological mapping of the global moon in China by using the data of Chang'e-II and also for regional geological comprehensive study and geological mapping of other celestial bodies in the future.

[24]
Dong J, Peng R C, Zheng Y D, 2013. An improved algorithm of point-by-point interpolation by using local dy- namic optimal Delaunay triangulation network.Geomatics and Information Science of Wuhan University, 38(5): 613-617. (in Chinese)For the problem that traditional algorithm of point-by-point interpolation based onDelaunay triangulation network can not give attention to both interpolating precision and executing efficiency,and according to the geometry characteristics of both Voronoi cells andDelaunay triangles,the paper brings forward the algorithm of point-by-point interpolationbased on local dynamic optimal Delaunay triangulation network.Some experiments that interpolating multibeam survey data into grid digital depth model(Grid-DDM),have been doneto validate the algorithm's validity.The experiment results show that the algorithm is characterized by good interpolating precision,meanwhile,the executing efficiency is also improved.

[25]
Dong Y F, Tang G A, 2012. Research on quantification model for elevation point's terrain information based on DEMs.Geographical Research, 31(10): 1825-1836. (in Chinese)For a given point embedded in grid DEMs,its comprehensive quantification model of terrain information content representing its significance in approximating the true terrain surface is constructed on the basis of information theory after its terrain syntactic information content is measured with differential geometry algorithm,and its terrain semantic information content is determined according to the terrain feature type and the global terrain structure.Then,choosing a study area of 70 km2 in the loess gully region with a resolution of 5 m,the paper discusses the extraction procedure of the terrain information content for a grid point based on grid DEMs and an application in multi-scale terrain generalization based on grid point's terrain information content.Experimental results show that the terrain information measurement model for a grid point is feasible and the multi-scale DEMs reconstruction method is not only easy to implement but also effective in reducing terrain distortion by preferentially keeping a set of "surface-specific" structural points located in global terrain skeletons.The application example proved that the multi-scale DEMs constructed by selecting critical points based on their terrain information content values could meet the demands of digital terrain modeling in different terrain scales.Therefore,the research could be helpful in deepening our understanding of DEM terrain information characteristics and offering a theoretical and methodological support for multi-scale digital terrain modeling.

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[26]
Dong Z L, Zhang G F, Jia J Yet al., 2014. Efficient keyframe-based real-time camera tracking.Computer Vision and Image Understanding, 118(2): 97-110.We present a novel keyframe-based global localization method for markerless real-time camera tracking. Our system contains an offline module to select features from a group of reference images and an online module to match them to the input live video for quickly estimating the camera pose. The main contribution lies in constructing an optimal set of keyframes from the input reference images, which are required to approximately cover the entire space and at the same time to minimize the content redundancy among the selected frames. This strategy not only greatly saves computation, but also helps significantly reduce the number of repeated features. For a large-scale scene, it requires a significant effort to capture sufficient reference images and reconstruct the 3D environment. In order to alleviate the effort of offline preprocessing and enhance the tracking ability in a larger scale scene, we also propose an online reference map extension module, which can real-time reconstruct new 3D features and select online keyframes to extend the keyframe set. In addition, we develop a parallel-computing framework that employs both GPUs and multi-threading for speedup. Experimental results show that our method dramatically enhances the computing efficiency and eliminates the uttering artifacts in real-time camera tracking. (C) 2013 Elsevier Inc. All rights reserved.

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[27]
Du M, Li M H, Yan Pet al., 2009. Quality control of full digital photographic surveying on DEM production.Geomatics & Spatial Information Technology, 32(4): 222-224. (in Chinese)From the point of view of productive practice,this paper discussed the production of practical data of full digital elevation model DEM,as well as its content and methods of quality inspection based on the techniques of full digital elevation model.

[28]
Florinsky IV, 2017. Spheroidal equal angular DEMs: The specificity of morphometric treatment.Transactions in GIS. doi: 10.1111/tgis.12269.Abstract Digital elevation models (DEMs) are commonly constructed using two main types of regular grids: plane square grids and spheroidal equal angular grids. Methods and algorithms intended for plane square-gridded DEMs should not be directly applied to spheroidal equal angular DEMs. This is because these grids have fundamentally different geometry. However, some researchers continue to apply square-grid algorithms to spheroidal equal angular DEMs. It seems appropriate to consider once again the specifity of morphometric treatment of spheroidal equal angular DEMs. This article, first, demonstrates possibilities of direct calculation of local, nonlocal, and combined morphometric variables from spheroidal equal angular DEMs exemplified by slope gradient, catchment area, and topographic index. Second, the article shows computational errors when algorithms for plane square-gridded DEMs are unreasonably applied to spheroidal equal angular DEMs. The study is exemplified by two DEMs. A medium-resolution DEM of a relatively small, high-mountainous area (Mount Elbrus) was extracted from the SRTM1 DEM. A low-resolution DEM of a vast region with the diverse topography (the central and western regions of Kenya) was extracted from the SRTM30_PLUS DEM. The results show that application of square-grid methods to spheroidal equal angular DEMs leads to substantial computational errors in models of morphometric variables.

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[29]
Fu B J, Zhao W W, Chen L Det al., 2005. Assessment of soil erosion at large watershed scale using RUSLE and GIS: A case study in the Loess Plateau of China.Land Degradation & Development, 16(1): 73-85. (in Chinese)Soil erosion is a serious problem in the Loess Plateau of China, and assessment of soil erosion at large watershed scale is urgently need. This study used RUSLE and GIS to assess soil loss in the Yanhe watershed. All factors used in the RUSLE were calculated for the watershed using local data. RUSLE-factor maps were made. The mean values of the R-factor, K-factor, LS-factor, C-factor and P-factor were 970 209 MJ km(-2) h(-1) a(-1), 0.0195 Mg h MJ(-1) mm(-1), 10.27, 0.33359 and 0.2135 respectively. The mean value of the annual average soil loss was found to be 14 458 Mg km(-2) per year, and the soil loss rate in most areas was between 5000 and 20 000 Mg km(-2) per year. There is more erosion in the centre and southeast than in the northwest of Yanhe watershed. Because of the limitations of the RUSLE and spatial heterogeneity, more work should be done on the RUSLE-factor accuracy, scale effects, etc. Furthermore, it is necessary to apply some physical models in the future, to identify the transport and deposition processes of sediment at a large scale. Copyright (c) 2005 John Wiley S Sons, Ltd.

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[30]
Gao C, Jin G J, 2012. Effect of DEM resolution of results of the SWIM hydrological model in the Changtaiguan Basin.Geographical Research, 31(3): 399-408. (in Chinese)

[31]
Gao J F, Han C L, 1999. Polders in Taihu Lake region and its effects on floods.Journal of Lake Sciences, 11(2): 105-109. (in Chinese)Concept and the present situations of polders in the Taihu lake region are introduced in this paper. Polders have been built to defense floods effectively, but it has made the drainage of basin not smooth. Built polders have effects on tile flood regime of Taihu Lake region, i. e. (l ) The areas of water surface and capacities of store water are reduced; (2) Natural water networks are changed; (3) Run-on and runoff are affected by human activities, the increasing of pump Power made runoff time much shorter than before. Based on the analysis, some methods of flood control in polders are given.

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[32]
Gao M X,Liu S F, 2013. Pleistocene paleosurface reconstruction and Holocene erosion quantity calculation for Guide-Gonghe-Tongde basin complex, Qinghai.Remote Sensing for Land and Resources, 25(1): 99-104. (in Chinese)The Guide-Gonghe-Tongde basin complex is located along the northeast marginal zone of the Tibetan Plateau.The Yellow River flows through these three basins.For understanding the tectonic and climatic indications of the fluvial erosion of the three basins since Holocene,the authors calculated the erosion quantity by using geological cross sections combined with digital elevation model(DEM).First,the points selected for the interpolation were picked out manually from a series of geological profiles.The minimum Pleistocene surfaces were reconstructed within the basins.This method reduced the error caused by the erosion after the deposition.Second,the erosion quantity and the erosion rates since Holocene were obtained by subtracting the modern elevation from the reconstructed surface.The results show that the erosion rate increased from upstream basin(Tongde basin) to downstream basin(Guide basin).The spatial erosion differences may indicate that the uplift of the margin of the Tibetan Plateau was greater than that of the inner part of the plateau.

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[33]
Gao Y P, 2010. Research on the DEM modeling methods of plain river network area [D]. Nanjing: Nanjing Nor- mal University. (in Chinese)

[34]
Gong J Y, 1992. A unified data structure based on linear quastrees.Acta Geodaetica et Cartographica Sinica, 21(4): 259-266.A data structure plays an outstanding role in GIS It is directly related to the func tion and efficiency of a GIS A new generation GIS should be capable of integrating various data of GIS DEM arid RS To serve this erjd, this paper proposes an unified data structure which has the properties peculiar to both, vector and raster. This structure is based on linear quadtree encoding for increasing the, geometric accuracy of raster representation and speeding database indexing use is made of multi-grid technique It can replace conventional vector and raster data structure and has the advantages of main taining better accuracy compressing storage space representing topological and spatial relations among various features and supporting object-oriented data models It can serve as a base of future GIS

[35]
Guo F, Liu X R, Ren L L, 2000. A topography based hydrological model: TopModel and its widened application.Advances in Water Science, 11(3): 296-301. (in Chinese)This paper describes the theretica l background of the TOPMODEL and the variable-source-area concept of stre am flow generation as well as the characteristics of TOPMODEL simulating hydrologic al response using different spatial distributions of the topographic index. A ll of the TOPMODEL's applications be fore are only limited on hillslope scale,the paper tries to widen the range of its applications and tests its applied result in ordinary catchment.Huaihe ba sin is chosed as the study area, and the TOPMODEL is made preliminary compa rison with the Xinanjiang model

[36]
Guo H, Gong W F, Kong D, 2009. DEM-based quantitative analysis of soil erosion: A case study of Maoershan region.Journal of Natural Disasters, 18(3): 139-145. (in Chinese)Based on the platform of ArcGIS9.0,the evaluation model of soil erosion was made by using usual soil loss equation,the cell based on the soil loss and erosion intensity was calculated by using attribute data and spatial data that include DEM,land use types and soil types.The terrain factors(elevation,slope and aspect) and distribution index was overlapped to quantitatively analyse the region soil erosion,which could study the soil erosion spatial distribution from terrains factors(elevation,slope and aspect).The results shown that weak and moderate erosion occupies dominant ratio on the whole;on the soil erosion distribution of aspect,the distribution of mild,intensive and strongest grades erosion is main in the half-sunny and sunny aspect;the moderate and mild erosion occupies a certain ratio in various elevation grades,which shows that there is no linear relation between soil erosion intensity and elevation.

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[37]
Guo Y J, Pan M, W Zet al., 2009. Based on drilling data and constraints of intersected folded cross-sections.Geography and Geo-Information Science, 225(2): 23-26. (in Chinese)

[38]
Han H H, Gao T, Yi Het al., 2012. Extraction of relief amplitude based on change point method: A case study on Tibetan Plateau.Scientia Geographica Sinica, 32(1): 101-104. (in Chinese)Choosing scientific method to extract and express relief amplitude has become the critical factor to improve the effectiveness and practicality in relief research.Based on SRTM3-DEM,the relief amplitude with increasing grid window method in the Tibetan Plateau was extracted,and then the best window area by the mean change point method was calculated.The result shows that 1.17km2 could be the best window area,the relief amplitude can be divided into eight classes,and the most widely distributed class is low rolling mountain.The relief amplitude is generally more violent at the edge of the plateau.It is mainly due to the intensive tectonic movement and river headward erosion.While the terrain is relatively flat in hinterland of the plateau,the erosion and removal caused by glaciation and unfreezing may be the greater impact on the relief amplitude.

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[39]
Hao C Y, Xu C Y, Wu S H, 2009. Total solar radiation spatialization in mountainous region based on DEM and climatological calculation.Resources Science, 31(6): 1031-1039. (in Chinese)

[40]
He S J, Chen J P, Li Ket al., 2012. The morphological classification and distribution characteristics of the craters in the LQ-4 Area.Earth Science Frontiers, 19(6): 83-89. (in Chinese)The major circular structures on lunar surface are craters,volcanic rings and lunar fornix.The most widespread geologic tectonic elements on lunar surface are craters.Because there are a great number and a large variety of craters,their formation processes are proceeding along with the evolution of the entire lunar geology.These lunar surface structures may give us a nearly complete record of the processes and types of transformation of lunar surface landforms over time,and the history of the planet.On the basis of the remote sensing images and the morphological characteristics of the impact craters,the craters on the moon can be classified into 7 types,including the normal,bowl-shaped,flat-bottomed,central mound,complicated and residual craters.Using the Chang'e- images and the LROC data and viewing from the structure and material aspects,we have compiled the new morphologic(crater floor,crater rim crest,crater wall,crater rim,crater rim material,and central peak) and morphometric(diameter,depth,longitude and latitude) data of the craters in the LQ-4 area.The results showed that the craters in the LQ-4 area could be categorized according to their spatial distribution,i.e.,those in lunar mare area and those in highland area.In the lunar highland area,the craters are mainly small or medium-sized,distributed with high-density and inhomogeneous,and those in the lunar mare area are fresh,with larger diameters,distributed with low-density.

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[41]
He W H, Yang X, Tang G Aet al., 2012. Research on sky view factor in urban area based on urban digital eleva- tion model: A case study of Nanjing old city.Journal of Geo-information Science, 14(1): 94-100. (in Chinese)The sky view factor(SVF) has been commonly used to describe the shadow impaction of visualization or sunshine from neighborhood buildings or terrains in urban area.It reflects the influences of urban geometry on the microclimate in an urban area.Firstly,we provided a comprehensive review of SVF analysis both in natural terrain and urban area studies.Then we presented a simulation approach based on shadow casting algorithm to calculate continuous SVF values.And,using raster-based data model we analysed the effect of sun shadow shading by neighbor buildings,simulated solar radiation for many times by continuing translation of the solar altitude and azimuth and calculated whether cells were in shadow.The ratio of simulation times and the times of a cell in shadow is considered as an approximate value of SVF.An ArcGIS-embedded computer program is developed and a SVF map for entire area is generated by using high resolution urban digital elevation model of Nanjing old city.Some areas representing different land use types in Nanjing old city are selected for analysis of the small-scale spatial variation of the SVF.The result illustrates that SVF decreases as building height raises or building quantity increases.Mean,maximum,minimum and standard deviation of SVF for each land use category within Nanjing old city are calculated and they are significantly different in different areas.The mean SVF values occurring in parks,open space and areas of historical and cultural value are higher than those of other land use types,which are more than 0.8.The mean SVF values occurring in community centers and residential areas are lower than those of other land use types,which are lower than 0.6.One of the most noticeable results is the unexpectedly higher mean SVF value in commercial areas than that in residential area in Nanjing old city.Meanwhile,spatial distribution pattern of SVF is derived by regarding block as a basic statistical unit.The mean values in the city centre are high while that in urban fringe are usually low.The blocks with high values line up in a northwest to southeast alignment,which may have an effect on urban microclimate.

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[42]
Hengl T, Reuter H I, 2008. Geomorphometry: Concepts, Software, Applications. Amsterdam: Elsevier, 772.

[43]
Hu H, Yang C Y, Hu P, 2007b. Optimal linear method for DEM generation: MADEM. Journal of Huazhong Uni- versity of Science and Technology (Natural Science Edition), 35(6): 118-121. (in Chinese)DEM generation method and its high precision and fidelity were discussed.It is pointed out that the truncation error of interpolation model should be considered as the main error in estimating the error of DEM generation method.A new DEM generation method basing on map algebra is given.It is in fact a linear interpolation on horizontal projection of the steepest descent line realized by recursive powered Voronoi interpolation between evaluated points and lines.Its precision is much better than that of the DEM generation methods basing on linear interpolation on Delaunay triangulation under the same conditions,and it also has the feature of high fidelity.Having compared with other methods,the DEM generation method should be the best linear interpolation method of all.

[44]
Hu J P, Wang X Y, Liu X J, 2014. A method of abnormal behavior detection in interrogation room based on video analysis combined with micro-spatial environment.Journal of Geo-Information Science, 16(4): 545-552. (in Chinese)The detection of anomalous human behaviors has received tremendous attention in the research of intelligent video analysis. However, most of existing methods for anomaly analysis are based on image space, and abundant information in the geographical space goes unused. In fact, human activities are closely related to geographical spaces, and different scenario types may correspond to different classes of human behaviors. So, in this paper we chose interrogation room as a representative of the micro-spatial environment and conducted a study on the anomaly detection of extorting confessions by torture, considering the spatial constraints. Firstly, the concept of behavioral variables has been stated, and then behavioral variables and their classes of extorting confessions by torture have been deeply analyzed. Secondly, the video characters of behavioral variables of extorting confessions by torture have been discussed and their corresponding detection models have further been designed. Plus,a bi-directional mapping model between the geographical space and the image space has been constructed according to vanishing points. This proposed mapping method can effectively avoid the calculation of intrinsic and extrinsic camera parameters. Based on above, a hierarchical and classified strategy for anomaly detection of extorting confessions by torture has been developed, considering the spatial constraints to human behaviors without learning and training processes. At last, the presented method in this paper is tested and verified by a series of simulated experiments.

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[45]
Hu P, Yang C Y, Wu Y L et al., 2007a. New Methods, Principles and Applications of Digital Elevation Model. Beijing: Surveying and Mapping Press, 56-58. (in Chinese)

[46]
Huang P Z, 2001. A new method for extracting terrain feature lines from digitized terrain data.Geomatics and Information Science of Wuhan University, 26(3): 247-252. (in Chinese)Ridge and valley are of essential important feature of terrain surface.They play an important role in the terrain representation because the basic structure of terrain is determined by these terrain feature.Digitized contour data contains the information of these feature lines implicitly.For many years,researchers have been working on the extraction of terrain feature lines from digitized contour lines.Up to now,existing method for feature line extraction is 2D geometrical analysis method,which includes extraction of feature points and feature line tracing.The former can be well solved by 2D geometrical analysis,but the latter is very difficult and remains unsolved because of the limitation of 2D geometrical analysis. In this paper,the author investigates the problem of the derivation of terrain feature lines,and discusses the existing method for the derivation of terrain feature line.After analyzing the existing method theoretically,the author puts forward an idea for terrain feature line tracing in which 3D terrain analysis technique is used.The new idea is based on the fact that vellay line is the line into which falling water is merged and ridge line is the line which separates falling water. The method for terrain feature line tracing developed by the new idea includes 3D terrain analysis and 2D geometrical analysis.Because 3D terrain analysis means falling water analysis in this paper,it is also called physical analysis of terrain model.In the falling water analysis of terrain,the lines into which falling water is merged and the line which separates falling water can be roughly located by falling water simulation.Because the conception of valley line and ridge line differs from the conception of the lines into slightly,some adjustment must be done before the valley line and ridge line are determined.The adjustment includes that some problems are led by differences between conceptions,and the location is not accurate by falling water simulation.The former means that there exist some mistakes at the two ends of the line into which falling water is merged because the accumulation of falling water has close relation to elevation.It leads to some part of valley line at higher position loss because the accumulation of falling water is small,and some part of the line into which falling water is merged at lower position is taken as parts of valley line because the accumulation of falling water is larger.The latter is led by the lower accuration of the data used in 3D terrain analysis.In the new method,2D geometrical analysis technique is combined with 3D terrain analysis,and the rough results of falling water simulation are used to guide the selection and ordering of feature points from 2D geometrical analysis results.In this way,the new mathod can take the advantages of 2D geometrical analysis and 3D terrain analysis,and overcome the shortcomings of them.At the end of this paper,the author gives an experimental result which shows the valley and ridge extracted by the new method is concord to the experimental terrain.

[47]
Huang Q, Ping J S, Su X Let al., 2009. New features of the moon revealed and identified by CLTM-s01.Science China Series G, 39(10): 1362-1370. (in Chinese)Previous analyses showed a clear asymmetry in the topography,geological material distribution,and crustal thickness between the nearside and farside of the Moon. Lunar detecting data,such as topography and gravity,have made it possible to interpret this hemisphere dichotomy. The high-resolution lunar topographic model CLTM-s01 has revealed that there still exist four unknown features,namely,quasi-impact basin Sternfeld-Lewis (20°S,232°E),confirmed impact basin Fitzgerald-Jackson (25°N,191°E),crater Wugang (13°N,189°E) and volcanic deposited highland Yutu (14°N,308°E). Furthermore,we analyzed and identified about eleven large-scale impact basins that have been proposed since 1994,and classified them according to their circular characteristics.

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[48]
Huang S Y, Wang L C, Chen X Let al., 2011. A semi-distributed hydrological model and its application based on a plain river-net area.Resources and Environment in the Yangtze Basin, 20(Z1): 44-50. (in Chinese)Poyang Lake area is a plain river-net area.The hydrologic observation and calculation is difficult in this area.A semi-distributed hydrological model was developed based on plain river-net area.Considering the topography and hydrology character,runoff calculation was divided into four underlying surfaces.Confluence calculation was based on hilly regions and plain regions.Model parameters were validated by the observed data of Boyang River watershed in 1982,1985 and 1986,and the runoff process could be accurately simulated.The model was used to simulate the hydrological process in the Poyang Lake area in 1983 and 1986 after being properly calibrated and validated in Boyang River watershed.The results showed that the annual runoff coefficients were 0.57(1983) and 0.46(1986),and the annual water quantity of Poyang Lake area accounted for 13.21%(1983) and 13.14%(1986) of total Poyang Lake watershed,which well agreed with hydrological theory.This semi-distributed hydrological model provides framework for other area without observed data and provides reference for the study of flood in Poyang Lake.

[49]
Huang W, Deng C, Day M J, 2014b. Differentiating tower karst (fenglin) and cockpit karst (fengcong) using DEM contour, slope, and centroid. Environmental Earth Sciences, 72(2): 407-416. doi: 101007/s12665-013-2961-3.The complex geometry of tropical karst landforms poses particular challenges for morphometric analysis, morphological classification and evolutionary assessment. Detailed geomorphological studies of the two most spectacular forms—tower karst (fenglin) and cockpit karst (fengcong)—have employed time consuming and labor intensive field surveys, which have yielded inconclusive and ambiguous results. This paper tests a novel discriminatory approach utilizing contour, slope and centroid derived from the ASTER Global Digital Elevation Model to differentiate between cockpit and tower karst in the Guilin area of southern China. Morphological indices are calculated to compare and contrast geomorphic variations using Object-Based Image Analysis (OBIA). The results suggest that the method provides a feasible means of differentiating between tower and cockpit landforms, and that OBIA offers a fast and semi-automatic way to extract morphological parameters.

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[50]
Ji Y P, Gao H S, Pan B Tet al., 2011. Implication of active structure in the upper reaches of Weihe river basin from stream length-gradient index (SL index) and Hack profile. Journal of Lanzhou University (Natural Sciences), 47(4): 1-6.The stream length-gradient SL index,Hack profile and gradient index(SL/K) were examined forconcavity studies of each profile and analyzed for research into the tectonic activities based on DEM.Themorphology of all hack profiles is convex,which show that the main factor causing the landform is tectonicuplifting in the upper reaches of Weihe river basin.However,the tectonic processes are distinguished in differenttributaries.The tectonic activities are very strong in the western Qinling and Liupanshan mountain areas andweak in the loess region of the northern study area.SL parameters have also proved the activity of westernQinling fault,Liupanshan eastern fault and Huining fault from quaternary.

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[51]
Jia J J, Lv G N, Song Z Yet al., 2000. Simulation of mechanisms for the tidal wave system in marginal seas, eastern China.Oceanologia et Limnologia Sinica, 31(2): 159-167. (in Chinese)Based on a three dimensional and high resolution numerical model, some factors associated with the marginal seas adjacent to eastern China (including the Bohai, Yellow and Eastern China Seas), such as the Coriolis acceleration, tide amplitude and phase on the outer boundary, seabed topography, coastline configuartion, and frictional coefficient are studied with the aid of Geographic Information System (GIS) in order to understand the respective impact of these factors upon the tidal wave system. According to the present study, moderate changes in the tide amplitude and phase on the outer boundary, the seabed topography and the frictional coefficient has little effect on the tidal wave system. However, the transformation of coastline configuration has remarkable consequences within the tidal system, and so does the tremendous changes of the seabed topography. Since in reality the input data of tide amplitude and phase, the Coriolis acceleration, the seabed topography and frictional coefficient are comparatively stable, the tidal wave system in the marginal seas adjacent to eastern China is a combined result of tide and marine environment. The marine conditions, especially the coastline configuration, are the predominated factors affecting the tidal-wave system. In a sense, the tidal amphidroms and tidal amphidromic system are controlled mainly by the coastline configuration over this region.

[52]
Jia Y,Li Z, 2014. Reconstruction of dense point cloud using space-patch model from sequence images.Geomatics and Information Science of Wuhan University, 39(12): 1430-1434. (in Chinese)Reconstruction method of dense point cloud using space-patch model(SPM) from sequence images is proposed. Considering gray consistency constraints and space geometric constraints of SPM，dense SPM are generated to approximating surface by selecting，expanding and filtering of seed points. This method is beyond the constraints of rigorous conditions of traditional dense matching of epipolar images.Experimental results show the validity of the algorithm and moreover. Kind of compartitive experiments are applied to analyzing that how iterations of expansion and filter influencing the quality of point cloud. The results show that massive 3D point cloud can be reconstructed by using repeatedly iterations of expansion and filter from high resolution images.

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[53]
Jiang H B, Zhang W Z, Qi Yet al., 2013. Research progress on accessibility to regional transportation infrastructure.Progress in Geography, 32(5): 807-817. (in Chinese)With the rapid development of regional transportation infrastructure in our nation,the research on accessibility to transportation infrastructure has been increasingly receiving attentions from academia and scholars in planning field.This article attempts to review the literature of domestic and foreign studies on accessibility to regional transportation in the recent 20 years,summarize characteristics and prospects of the studies from the aspects of temporal-spatial variations of accessibility and the aspects of its regional spatial effect,and predict hot topics of the related domestic research in the future.Through systematically comparing the similarities and differences of domestic and foreign research,we conclude that the research on temporal variations of regional accessibility is still an important topic at home and abroad.As shown in the related foreign literature,there are numerous evaluation indicators;spatial resolutions of accessibility have been continuously improved;more and more analytical technique and methods are being developed.When simulating accessibility,more complex and realistic factors are taken into account,such as traffic congestion,transfer,etc.Foreign research tends to be more diversified,and continues to explore new fields and new applications,such as spillover effect,etc.In the related domestic literature,the research develops quickly and adopts foreign research methods and ideas,but more studies on index system are needed and spatial resolution needs to be further improved.We should also consider more important realistic factors in accessibility research,such as traffic demand and policy intervention etc.

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[54]
Jiang H Q, Zhang G F, Dong Z Let al., 2008. Fast interactive scene modeling from an image sequence.Journal of Computer-Aided Design and Computer Graphics, 20(9): 1196-2003. (in Chinese)ABSTRACT This paper introduces an image-sequence-based interactive 3D modeling system. Given an uncalibrated image sequence or a video, the system can automatically recover the camera motion parameters. After simply drawing strokes or curves along the shape of the scene object on a few frames, the system can analyze the user interactions and help making the correspondences among multiple frames. Then 3D models of the objects in the images can be accurately reconstructed. This system provides reconstruction tools for modeling primitives of points, lines, planes, curves and surfaces, etc. It can meet the requirements of rapidly reconstructing realistic 3D models for real-world complex scenes. Several real-world examples are presented to demonstrate the effectiveness and usefulness of the proposed system.

[55]
Jiang L, Tang G A, Zhao M Wet al., 2013. Extraction and analysis of loess gully heads considering geomor- phological structures.Geographical Research, 32(11): 2153-2162. (in Chinese)

[56]
Jin C, Lu Y Q, Fan L L, 2010. Research on accessibility of scenic spots in the Yangtze River Delta based on land traffic network.Journal of Natural Resources, 25(2): 258-269.Transit route system is link between tourist destination and tourist market,and then good transit system will provide an important theoretical basis for optimizing distribution of scenic spots for government branch.This paper analyses the accessibility of scenic spots in the Yangtze River Delta quantitatively with ARCGIS software.The results show that the accessibility of scenic spots is good,the regional average accessibility is about 25.89 minutes,and the area where the accessibility of scenic spots is within 30 minutes reaches 69.79%,while the area where the accessibility is within 1 hour accounts for more than 5% and the longest time needs 191.86 minutes which is located at the edge of this region.And then,distribution of the accessibility has pointed to traffic lines,such as Shanghai-Nanjing Railway Line and Shanghai-Hangzhou Line.Considering the accessibility,we find that the human scenic spots are more centralized,such as in Shanghai,Suzhou and Wuxi,which are better than the natural scenic spots.Then,the average accessibility between natural scenic spots and human scenic spots are 30.82 and 33.94 minutes,respectively.As for the distribution of the accessibility value within 30 minutes,the natural scenic spots are 2.67% higher than the human scenic spots,in the same way,3.41% higher within 60 minutes.At county level,the estimated values of Moran's I are all positive numbers using analysis of spatial association.All the test results indicate that scenic spots and adjacent areas show weak positive correlation.Distribution of hot spots regarding the accessibility shows a concentric pattern,which the core is Shanghai.Cold spots are distributed in the periphery of the Yangtze River Delta.Shanghai has the shortest time for the whole accessibility,with the time of 5.46 minutes.The second one is Pudong New Area and the longest one is Chengsi county in Zhoushan with the time of 156.07 minutes.On the basis of the above results,we summarize four factors which impact the accessibility of scenic spots: distributing of scenic spots,the structure of traffic,human environment and nature environment.The former two and the latter two factors are the direct and indirect causes respectively,mainly by means of distribution of scenic spots and the structure of traffic.

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[57]
Jin H L, Kang J R, Gao J X, 2006. Research on the algorithm of extracting ridge and valley lines using contour data.Geomatics and Information Science of Wuhan University, 30(9): 809-812. (in Chinese)In this paper, the authors put forward a brief and practical arithmetic for auto extracting terrain lines from digital terrain data after analyzing and comparing current arithmetics. This paper gives an experiment result that the ridge and valley extracted by the arithmetic is consistent with the experimental terrain.

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[58]
Kong J, Song Z Y, Zhang J Set al., 2008. Research of the effluence of tidal level on wind drag stress coefficient in- storm surge model.Marine Forecasts, 25(1): 74-79. (in Chinese)Storm surge model has been used widely to simulate the non-astronomical tidal set-down and set-up occurring in typhoon season.In model there are many formulas about wind stress coefficient can be used to calculate the wind drag stress on free surface.But in conventional formula only the relative wind speed is considered without considering the effluence of tide level.Actually in intensive estuarine and coastal area,the tidal range is large,even reaching half of the reference height of 10m,such as the Yangtze estuary and Hangzhou bay.So the precision of model will be reduced because the wind stress is underestimated in flood tide and be over-valuated in falling tide without considering the fluctuation of water itself.Therefore the relationship of the relative wind speed and water elevation should be considered together.A new kind of wind stress formula has been established in this paper and used to simulate the storm surge of typhoon Winnie in Yangtze Estuary and Hangzhou bay.The results are better and satisfying.The new formula can be used in the future storm surge model in intensive estuarine and coastal areas.

[59]
Kong Y P, Fang L, Jiang Y Let al., 2012. A new method of extracting terrain feature lines by morphology.Geo- matics and Information Science of Wuhan University, 37(8): 996-999. (in Chinese)There are some fast and effective methods related to image processing technique.But they are unsatisfactory in resisting the noise and in reducing the redundant information.For this situation,a new method of extracting terrain feature lines is proposed by the mathematical morphology.Considering the characteristics of the ridges and valleys,two kinds of operators are designed by basic morphological operation.Then the new method is built on the operators with iterative forms.The experimental results show that the ridge-lines and valley-lines extracted by the method fit the real terrain.And it can resist some small-scale noise.

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[60]
Kong Y P, Yi W, Zhang Y P, 2013. Extracting saddle point fast based on topological relationship.Computer Engi- neering and Applications, 49(16): 165-167. (in Chinese)Based on the analysis of the saddle’s characteristics, extract the feature points by using the mobile window method, then layer the grid DEM data in order to simulate the geomorphic characteristics of contour map. Thus distinguish them by examining the topological relationship with its’ surrounding area. The experimental results show that the algorithm is fast, simple and fit the landform cognition.

[61]
Lan H X, Wu F Q, Zhou C Het al., 2002. Analysis on susceptibility of GIS based landslide triggering factors in Yunnan Xiaojiang watershed.Chinese Journal of Rock Mechanics and Engineering, 21(10): 1500-1506. (in Chinese)Analysis is made on the landslide triggering factor susceptibility in Xiaojiang watershed,Yunnan by means of landslide certainty factor (CF). The presented results are helpful to study the landslide mechanism and spatial distribution characteristics. The factors contributing the landslide occurrence are determined,including lithology,structure,slope,elevation and faults,etc..

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[62]
Lang L L, Cheng W M, Zhu Q Jet al., 2007. A comparative analysis of the multi-criteria DEM extracted relief: Taking Fujian low mountainous region as an example. Geo-Information Science, 9(6): 1-6, 135-136. (in Chi- nese)The slope and relief are commonly used parameters in describing terrain.In the regional study,using the DEM data to draw relief can reflect the terrain characteristics fast and directly.The slope is mainly used to divide plain and mountain region,and the relief is mainly used to sub-divide the hills,small rolling mountain,middle rolling mountain and the great rolling mountain.The basic landform type is determined by criteria of relief and elevation,and it is also the foundation of division for more detailed landform classification by remote sensing.In this article,with DEM data including 1∶250 000 and 1∶100 000 of the study area,the slope is calculated to draw up plain and mountain region with a critical slope value of being approximately 3°;using the method of increasing grid window progressively in ArcGIS space analysis,which corresponds to different DEMS,the relief is calculated to determine the best window area which is set to be 4.41km2;and using statistical method based upon comparison several different measures of the existing research results,the functional map of the study area between relief and the best window area is worked out.This research has certain model function when extracting the basic landform type in low mountain and hilly regions.

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[63]
Li A B, Zhou L C, Lv G N, 2013. Geological Information System. Beijing: Science Press. (in Chinese)

[64]
Li C L, Liu J J, Ren Xet al., 2010. The global image of the moon by the Chang’e-1: Data processing and lunar cartography.Science China Earth Sciences, 40(3): 294-306. (in Chinese)The global lunar image of the first phase of Chinese Lunar Exploration Program is the first image that covered all over the surface of the Moon. It will serve as a critical foundation for succeeding exploration and scientific research. In this paper, the acquisition, characteristics, and data quality of Chang’E-1 CCD image data are described in detail. Also described are the methodology and procedure of data processing. According to rule of planetary cartography, the image data have been processed, geometrically corrected, and then mosaicked and merged in a scale of 1:2.5 million. The results of data processing and charting show that the image data of Chang’E-1 CCD and their geometric precision meet the demand of charting a map in the scale of 1:2.5 million. The relative geometric positioning precision of the global image is better than 240 m, and the absolute geometric positioning precision is slightly better than that of the ULCN2005 and Clementine lunar basemap (V2.0). The plane positioning precision is approximately 100-1500 m. This global image proves to be the best global image of the Moon so far in terms of space coverage, image quality, and positioning precision.

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[65]
Li D R, Chen X Y, 1990. Auto-generation of DTM triangulation based on mathematical morphology.Acta Geo- daetica et Cartographica Sinica, 19(3): 161-172. (in Chinese)

[66]
Li D R, Liu L K, Shao Z F, 2015. An integration of aerial oblique photogrammetry and mobile mapping system for urban geographical conditions monitoring.Geomatics and Information Science of Wuhan University, 40(1): 427-435. (in Chinese)为了丰富城市地区地理国情监测的成果并提高监测效率,实现了一个从天到地、从影像到模型、从静止到动态的城市环境监测系统.该环境监测系统管理航空倾斜多视成像仪和地面移动测量系统采集的航空与地面的可量测实景影像、兴趣点、实时视频及从倾斜影像中获得的数字高程模型数据和生成的三维模型,方便了监控、巡航和分析等多种业务需求.在贵阳市进行了验证,实现了安全巡航、建筑变化监测等功能,已成为高效的城市环境情况监测的解决方案.

[67]
Li F Y, Tang G A, 2006. DEM based research on the terrain driving force of soil erosion in the Loess Plateau. In: Gong Jianya, Zhang Jingxiong eds. Geoinformatics 2006: Geospatial Information Science, Proc. of SPIE Spie, 6420: 64201W-64201W-864201W. (in Chinese)DEM data availability and GIS-assisted processing of the data have extended the usage of DEM to a great extent. Taking 5 m grid resolution DEMs of 48 test areas in the Loess Plateau in north Shaanxi as test data, this paper introduces the definition, calculation, extraction and stable threshold area of terrain driving force (T ) for soil erosion. Then, spatial distribution of T is investigated with a method of geostatistics analysis. Results show that spatial distribution of T is correlatable with spatial distribution of the soil erosion intensity and T can be taken as a regional terrain factor of regional soil erosion in the Loess Plateau. But T is not exact enough in evaluation processing of regional soil erosion, an integrated analysis combining the climate, vegetation cover, soil and water conservation management is demanded. Then, some problems existing in the research of regional soil erosion are analyzed and a preliminary model of regional soil erosion contained T is proposed. Subsequent research is focused on data collection and integration of regional soil erosion and its applicability in the Loess Plateau.

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[68]
Li J, Sheng Y H, Zhang Ket al., 2014. Image matching of variable circular domain compass features.Optics and Precision Engineering, 522(5): 1339-1346. (in Chinese)As existing image matching algorithms show the problems of high computational complexity and uncertainty in point-pair selection, a Variable Circular Domain Compass Matching (VCDCM) algorithm was proposed. After key-points being detected by four compasses, the variable circular receiving domain was used to choose the ideal point-pairs. Then, the point-pair set was divided into two subsets according to the distance of point-pairs. The subset of long-distance pairs was used to describe the direction of a key-point and that of short-distance pairs was used to build the descriptor of key-point. Finally, key-points were matched by Hamming distance instead of traditional Euclidean distance, while the match points were filtered with Random Sample Consensus (RANSAC) algorithm to avoid mismatches caused by the noise and moving objects. Comparative experiments between Scale Invariant Feature Transform (SIFT) and Binary Robust Independent Elementary Features (BRIEF) algorithms were performed on the robustness and efficiency. The experimental results show that the proposed algorithm is faster with high accuracy and stability.

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[69]
Li P H, Lu Y Q, 2005. Review and prospectation of accessibility research.Progress in Geography, 24(3): 69-78. (in Chinese)Accessibility denotes the ease with which activities may be reached from a given location using a particular transportation system. Accessibility reflects the opportunities and potentialities of a particular region to exchange with other regions. There is a number of accessibility measures, some accessibility indicators are generalized and compared in this paper: time of access to city centre, mean travel costs, opportunity accessibility, economic or population potential. Also, the progress of accessibility measures is reviewed. Accessibility indicators is applied both on regional and metropolitan dimension, such as the regional development, the impact of new infrastructure, the urban land use, the providing of social facilities, the urban social problems, and so on. Relative to the overseas there is rarely research on accessibility in our country. Therefore, some problems are put up in the end and accessibility research needs to be improved.

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[70]
Li S, Lai Z Q, Wang Qet al., 2013. Distributed simulation for hydrological process in plain river network region using SWAT model.Transactions of the Chinese Society of Agricultural Engineering, 29(6): 106-112. (in Chinese)Distributed hydrological modeling plays an important role in water resource management and regional non-point source pollution assessment.The Soil and Water Assessment Tool(SWAT) is a popular modeling tool for understanding regional hydrological processes.However,the general approach based on the SWAT model was only applicable to the mountain and hilly dominated area.There is no effective way to modeling the hydrologic process in plain river network regions,which is characterized by large flat areas,consisted of many lakes and artificially hydrological polders,and intersected stream networks,etc.The existing methods cannot effectively extract the channels in flat and pit areas,parallel channels or discontinuous rivers and the definition error of the catchment areas.To overcome these problems,we developed a novel method for modeling the distributed spatial discretization of the plain river network area based on the SWAT model.There are three key techniques are discussed:making the rings and crossed rivers to dendritic stream networks by cutting the river ways shortly,restoring the distribution of water between reaches by transferring water from one reach to another one on the basis of flow rate of each reach and simulating the exchange of water inside and outside of the polders according to the scheduled rules of the polder areas by adding a 'virtual reservoirs' within the SWAT model.In this paper,the typical plain river network region located in western Taihu watershed was chosen as the study area,and a large number of basic geographic data such as topography,soil,climate and land use were collected and parameterized.The modeling procedures were used to simulate the monthly runoff of the area of western Taihu Lake from the year of 2008 to 2010,and the applicability of the method to the plain river network region was also verified.The simulated results matched mostly well to the observed data of Rongdengqiao,Hujiawei,and Yixing hydrological stations.The calculated Nash-Sutcliffe efficiency coefficient and correlation coefficient of three hydrological stations were 0.84,0.80,0.67 and 0.94,0.95,0.93,respectively.It indicated that our developed framework for the SWAT model was practical and capable of representing the hydrological processes in the plain river network regions.

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[71]
Li Y, Yang B, Yang Z Q, 2013. Extraction of ridge lines and valley lines from mountainous LiDAR ground point cloud.Journal of Geodesy and Geodynamics, 33(3): 111-115. (in Chinese)A method of the extraction of ridge lines and valley lines from mountainous LIDAR ground point cloud is presented.We extracted the normal vector and curvature of ground data based on differential geometry theory and local polynomial fitting,acquied the ridge points and valley points by computing extremum coefficient of curvature,generated ridge lines and valley lines based on the principle of minimum spanning tree.The results show that the method is feasible and effective.

[72]
Li Z L, Xu Z X, Li Z J, 2011. Performance of WASMOD and SWAT on hydrological simulation in Yingluoxia watershed in northwest of China.Hydrological Process, 25(13): 2001-2008. (in Chinese)Two hydrological models with different structures and spatial capabilities are selected to simulate the runoff and actual evapotranspiration (AET) in Yingluoxia watershed, the upper reaches of Heihe River basin in northwest of China, to validate their performances in simulating hydrological processes. They are calibrated against the observed runoff at the watershed outlet (Yingluoxia station) for the period from 1990 to 1996 and validated for the period from 1997 to 2000. Results show that in terms of the simulated hydrograph against observations and the two selected objective functions, the conceptual, lumped Water And Snow balance MODeling system (WASMOD) with simple model structure could give the same, even better results than the semi-distributed Soil and Water Assessment Tool (SWAT) with complex structure. Compared with other model applications to the watershed, simulation for monthly runoff made in this study seems better. With regard to AET, results calculated from both models are comparable as well. Both WASMOD and SWAT are proved to be suitable and satisfactory tools in simulating hydrological processes in the study area, although both of them have strengths and limitations in applications. WASMOD model may be one of the promising alternatives in hydrological modelling. Copyright 2010 John Wiley & Sons, Ltd.

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[73]
Li Z L, Xu Z X, Shao Q Xet al., 2009. Parameter estimation and uncertainty analysis of SWAT model in upper reaches of the Heihe River Basin.Hydrological Process, 23(19): 2744-2753. (in Chinese)Abstract Heihe river basin, the second largest inland river basin in China, has attracted more attention in China due to the ever increasing water resources and eco-environmental problems. In this article, SWAT (Soil and Water Assessment Tool; http://www.brc.tamus.edu/swat/ ) model was applied to upper reaches of the basin for better understanding of the hydrological process over the watershed. Parameter uncertainty and its contribution on model simulation are the main foci. In model calibration, the aggregate parameters instead of the original parameters in SWAT model were used to reduce the computing effort. The Bayesian approach was employed for parameter estimation and uncertainty analysis because its posterior distribution provides not only parameter estimation but also uncertainty analysis without normality assumption. The results indicated that: (1) SWAT model performs satisfactorily in this watershed as a whole, although some low and high flows were under- or overestimated, particularly in dry (e.g. 1991) and wet (e.g. 1996) years; (2) all calibrated parameters were not normally distributed (essentially positively or negatively skewed) and the parameter uncertainties were relatively small; and (3) the contributions of parameter uncertainty on model simulation uncertainty were relatively small. Copyright 2009 John Wiley & Sons, Ltd.

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[74]
Li Z W, Wang Z Y, Li Y Fet al., 2012. Planform geometry characteristics of typical meandering rivers in Yellow River Source.Journal of Sediment Research, (4): 11-17.The Baihe and Heihe rivers are tributaries in the Yellow River source region in the north-eastern part of the Qinghai-Tibet Plateau.The rivers are meandering with extremely high sinuosity and numerous oxbow lakes.Digital Elevation Model and Google Earth satellite images are used for analyzing the characteristics of the rivers,meanders and oxbow lakes.River networks and longitudinal bed profiles of the Baihe and Heihe rivers are extracted by using GIS model.Channel width,sinuosity,valley width and number of oxbow lakes are calculated with AutoCAD software.Average sinuosity of the Heihe River is 2.46,which is much greater than that of the Baihe River(1.68).It is found that the sinuosity of the Heihe river is greater than the Baihe River and the main causes for the big difference are their different average flow discharges and average channel gradients.The Heihe River has much higher density of oxbow lakes than the Baihe River.The density of oxbow lakes of the Heihe River is more uniform along the course which keeps a higher frequency of cutoffs.The density of oxbow lakes reduces along the course of the Baihe River because the channel width and average flow discharge increase along the course.

[75]
Liang F, Xu B, 2014. Discrimination of tower-, cockpit-, and non-karst landforms in Guilin, southern China, based on morphometric characteristics.Geomorphology, 204(1): 42-48.Depressions are well developed in certain types of karst landform assemblages. These natural depressions should not be simply filled and removed during the preparation of DEMs. This study presents a research to distinguish karst landform assemblages which tend to have natural depressions from other karst landform assemblages and non-karst landforms in the Guilin area of China, by examining their morphometric characteristics derived from a 30-m resolution DEM. The variations in the morphometric characteristics are examined at neighborhood level instead of pixel level. The DEM is divided into square tiles with a specific spatial scale. Statistical indicators of typical morphometric characteristics such as the area ratio, elevation, slope, and curvature are calculated for each tile. Discriminant analysis (DA) is then performed to discriminate tower karst, cockpit karst, and non-karst landforms. These procedures are repeated at the scales of 0.45, 0.9, 1.8, 2.7, 3.6, and 4.6 km. Comparison of the mapping results with a reference geomorphic map shows that the DA works best for the 2.7 km tiles with an overall accuracy of 80.06%. The resulting map can be used to guide whether depressions should be retained or removed during DEM preparation. This method, with appropriate modifications and improvements, can also be used to map the karst landforms of the whole of southern China. With such a comprehensive map, geomorphologists would be able to examine the development of karst landform assemblages at a broader view to unveil their genesis and evolution processes.

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[76]
Liang Y, Sheng Y H, Zhang K, 2013. Method on 3D dense point cloud recovery of geographical scene.Advanced Materials Research, 748: 619-623.The object of this research is to reconstruct 3D dense point cloud of geographical scene. With the technology and method of computer vision , first affine invariant features are extracted and matched, then cameras parameters and 3D dense point cloud are recovered and united under geographical reference. The experimental results show that this method with low cost and high precision of centimeters can satisfy the requirements of measurement, modeling and virtual reality.

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[77]
Liao M, Zhou L C, Lv G Net al., 2014. Theoretical analysis of the geometric relations between human stereo visional space and virtual 3D space.Computer Engineering and Science, 636(6): 1120-1126. (in Chinese)The virtual 3Dspace is a digital one of real world and the human stereo visional space is a3Dreconstruction of the real world or virtual scene through human visional system.Traditionally,human views the environment around himself directly and the geometric relationship between the human stereo visional space and the real world exists undoubtedly.How about the relations of stereo visional space to the virtual 3Dspace are?According to the principle of binocular disparity,ageometric model of stereo vision is established for the virtual 3D scene and the corresponding visional 3Dmodel is constructed too.And the screen disparity and retina disparity are analyzed with respect to an arbitrary spatial point.As a result,the geometric mapping between the point of virtual space and the one in visional space is established with matrix algebra,indicating that the 3Dvisional model can be mapped to a virtual3Dmodel unambiguously and the metric capability of human visional system is intrinsic.The main contribution of this paper is that a wholesome visional 3Dmodel is proposed,which lays down a quantitative analysis foundation for the traditional stereo vision.The results are useful theory explorations for the stereo presence,the virtual interaction and the metric applications.

[78]
Lin B X, Zhou L C, Lv G N, 2013. A 3D geological model construction approach based on virtual boreholes.Journal of Geo-Information Science, 15(5): 672-679. (in Chinese)Construction of 3D geological models is a very efficient way to create a good understanding of geological features.It is a comprehensive method to geologists,geophysics engineers and GIS experts who sometimes need to visualize an area to accomplish their researches.Geological drill hole records have been widely used as the main data sources in 3D geological model construction approaches.However,since the original drill hole sampling points are limited and maldistributed,it is difficult to construct 3D geological models that not only show favorable visual effect but also reflect accurately the geological structure of surveying regions.To solve this problem,this paper proposes a 3D geological model construction approach based on virtual boreholes.Firstly,according to the spatial distribution of original drill holes,positions of interpolated points are determined self-adaptively and Kriging interpolation algorithm is applied to the construction of interpolated virtual boreholes.Secondly,according to the pinch-out rules,the pinch-out virtual boreholes are constructed,and the improved self-adaptive butterfly subdivision algorithm is applied to the construction of subdivided smooth virtual boreholes.Finally,with the original drill holes,the interpolated virtual boreholes,the pinch-out virtual boreholes and the subdivided smooth virtual boreholes,3D geological models of survey regions can be constructed,matching geostatistics patterns,being C1geometric continued,and showing favorable visual effect.Differing from the traditional modeling methods that regard virtual boreholes as complements to expert knowledge,the proposed method introduces virtual boreholes into each step of the construction of three-dimensional geologic models as the intermediate elements of the core algorithm,simplifying the realization process of the modeling algorithm effectively,and ensuring the stability and efficiency of the algorithm.

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[79]
Lin H, Lv G N, Song Z Yet al., 1997. Study on modeling the tide wave system of East China Sea with GIS.Acta Geographica Sinica, 52(Suppl.1): 161-169. (in Chinese)This paper describes the systematic research on Tide Dynamic System under the support of Geographic Information System and ocean fluid dynamics model. Through the high resolu-tion numerical simulation, we found some previously unreported phenomena such as a low tide amplitude zone of M2 Constituent nearing Zhoushan isle, a low tide amplitude zone of K] Con-stituent nearing Taiwan isle, and circular flow point band. The results of this research also show that the formation of tide wave system are affected by sea bottom friction coefficient, to-pography under water and shore line morphology. The change of shore line morphology and huge change of topography under water play an important role in the tide wave system. Under specified conditions on input tide wave, shore line morphology has a dominant impact on the formation of the tide wave system. With the systematically reconstructed sea level and the coast change of thirty periods since full period of the last glacier, the evolution process of tide wave system of East China Sea was simulated. Based on the simulation analysis of relationships among topography, shore line and tide flow, the conclusion of this study shows that the char-acteristic of tide dynamic system is a dominant influencing factor on the formation of large scale sand ridge clusters. In this paper, the system integration of geographic information system, tide numerical simulation system and tide movement visualization system are discussed as an example for related studies.

[80]
Ling L, Burnett I S, Cheng E, 2012. A dense 3D reconstruction approach from uncalibrated video sequences.Proceedings of 2012 IEEE International Conference on Multimedia and Expro Workshops, Melbourne, Aus- tralia, 49(1): 587-592.Current approaches for 3D reconstruction from feature points of images are classed as sparse and dense techniques. However, the sparse approaches are insufficient for surface reconstruction since only sparsely distributed feature points are presented. Further, existing dense reconstruction approaches require pre-calibrated camera orientation, which limits the applicability and flexibility. This paper proposes a one-stop 3D reconstruction solution that reconstructs a highly dense surface from an uncalibrated video sequence, the camera orientations and surface reconstruction are simultaneously computed from new dense point features using an approach motivated by Structure from Motion (SfM) techniques. Further, this paper presents a flexible automatic method with the simple interface of 'videos to 3D model'. These improvements are essential to practical applications in 3D modeling and visualization. The reliability of the proposed algorithm has been tested on various data sets and the accuracy and performance are compared with both sparse and dense reconstruction benchmark algorithms.

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[81]
Liu C F, Li X M, Han D, 2010. Accessibility analysis of urban parks: Methods and key issues.Acta Ecologica Sinica, 30(19): 5381-5390. (in Chinese)Urban parks are the main places for leisure and recreation for urban residents and play significant roles in beautifying the cities and harmonizing the urban residents nature.With the rapid urbanization and fast increasing of people's living standard,urban residents not only yearn for more urban parks,but also expect to enjoy them conveniently.These changes present great challenges for urban park evaluating and planning.Accessibility analysis is a feasible choice to address this question.Accessibility is defined here as urban parks can be reached or obtained easily or not,which also can be regarded as an important evaluating indicator of urban park spatial distribution efficiency.As the main method to evaluate distribution efficiency and service equity of urban parks,accessibility can be analyzed by many methods.However,different methods are based on different theories and data requirements,reflecting different aspects of accessibility.Understanding these methods and their characteristics exactly will help us choose the suitable method for urban park accessibility analysis.We categorized these methods into four groups and six types and reviewed their theoretical basis,advantages and disadvantages.Although statistic index method is the most widely used,it can only acquire some basic information of urban parks(e.g.percent of urban park area,urban park area per capital)and neglect the spatial distribution of urban parks.Simple Buffering Method and Minimum distance method are simple methods which concern the location of urban parks.The main disadvantage of these methods is that they ignore the barriers between urban parks and residents.Cost weighted distance method measures the total or average distance between citizens and urban parks.Usually distance is calculated as cost weighted distance based on classified landscape.It assigns each landscape type a relative travelling cost and then generates a map of accumulated cost distance.This method depends on classified landscape and relative travelling cost but these values are usually assigned arbitrarily.Gravity Model is based on the law of the gravity.This method calculates relative values which are proportional to recreation opportunities of urban parks(area,recreational facilities)and inversely proportional to distance between urban parks and residents.These relative values spatially display the ease with which urban parks can be reached.However it is difficult to describe the distance decay factor exactly.Network Analysis Method calculates the actual distance or time cost between urban parks and residents based on the actual road.This method simulates the process people reach urban parks more exactly.There are four critical issues which need to be solved during urban park accessibility analysis:(1)simplifying the urban parks and urban citizens exactly,(2)simulating the actual resistance that people will overcome when reaching urban parks,(3)reflecting recreational attraction of urban parks objectively,and(4)choosing the suitable maximum service distance of urban parks especially for different groups of people.We recommend that more effective methods,which not only take the above issues into account,but also integrate the advantages of the previous methods,should be designed to provide more valuable and direct information for urban park planning.

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[82]
Liu C M, Li D F, Tian Yet al., 2003. An application study of DEM based distributed hydrological model on mac- roscale watershed.Process in Geography, 22(5): 437-445. (in Chinese)The paper selected the macro-scale areas of the source region of the Yellow River as an object and carried out discharge simulation with the distributed hydrological model,the SWAT model.Based on the analysis and process of DEM data,such as flow direction,a watershed borderline,a river network and sub-basins by automatically becoming,rivers,codes and areas of sub-basins,structure and topology constraint of the river network were gained with a format of grid cells.Annually and monthly measured runoff data of Tangnaihai hydrologic station from 1976～1985 were used to calibrate the simulation parameters and determine some basic parameters of the model.The simulation results are satisfactory and show that climate change is the main reason for discharge change of the source regions of the Yellow River.In twenty years of the 1980's and the 1990's,the discharge decrease due to climate change is 62.11×108m3/s,which accounts for 108.72% of total discharge change,and the discharge increase due to land-cover change is 5.73×108m3/s ,which accounts for 10.03% of that with grid cell.

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[83]
Liu D, Liu X J, Wang M Z, 2014. Automatic approach of lens radial distortion correction based on vanishing points.Journal of Image and Graphics, 319(3): 407-413. (in Chinese)

[84]
Liu H Y, Dongye G L, 2004. Research on the application of DEM in area soil erosion.Journal of Jilin Agricultural University, 26(1): 73-76. (in Chinese)Digital Elevation Mode (DEM) was made by relief map of the researched area, and slope and aspect were computed from the DEM. Through overlapping the DEM, slope and aspect, relationship among divisor, erosion type and erosion course was determined. The conclusion was that the types of soil erosion had obviously vertical distribution in Culai area. Different aspects made erosion intensity diverse obviously, and different ranges of slope led to diversity in the main soil erosion types.

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[85]
Liu K Z, Liu J, Feng X S, 2005. A kind of virtual implementation method of benthos terrain and current.Journal of System Simulation, 17(5): 1268-1271. (in Chinese)One kind of virtual implement method of benthos terrain and current in the ocean environment, which was used to realize AUV visual simulation, is presented. In order to get the more accuracy benthos terrain, not only the discrete electronic chart data but also the fathom lines etc data are considered. The simulation of the current can be adopted as two kinds of approaches: building current database, and calculating hydrokinetics. The research on the methods of ocean environment is of importance in the AUV terrain matching navigation, path planning and obstacle avoidance strategy etc. The results have been applied in the research work of our digital AUV platform.

[86]
Liu K, Tang G A, Tao Yet al., 2012. GLCM based quantitative analysis of terrain texture from DEMs.Journal of Geo-Information Science, 14(6): 751-760. (in Chinese)Terrain texture is an important natural texture.DEM based terrain texture attracts more attention in the research area for its purity in representing surface topography and its derivability in terrain analysis.In this paper,10 sample areas from different landform types of Shaanxi Province were selected to make a quantitative analysis on the terrain texture by Gray level co-occurrence matrix(GLCM) model.Experiments show that,when using the DEM data with 25m resolution,the suitable analytic distance of GLCM model is not less than 3 pixels.Among all the parameters in the model,correlation could be used for texture direction detection.Contrast,variance,and different variance could be applied for texture periodicity analysis.Entropy,angular second moment and inverse different moment are suitable for texture complexity investigation.In this research,quantitative analysis is conducted to terrain texture by using DEM data,hillshade data,slope data and curvature data.The terrain texture directivity experiment shows that the correlation of hillshade data reacts sensitively to the terrain texture direction and can detect main terrain texture direction.The correlation of slope data reacts obviously in rugged topography such as hilly region and mountainous regions so it can play an auxiliary role for hillshade data in the detecting of terrain texture direction.Results of terrain texture periodicity and complexity analysis shows that among DEM data and its derived data,the mean variation coefficient of each texture parameter based on hillshade data is the highest,and it further proves that the hillshade data is most suitable for quantitative analysis of terrain texture.Quantification is conducted by variance of hillshade data to texture periodicity of different terrain texture,variance eigenvalue of flat,platform,hill and mountain region gradually increases which indicates the increase of terrain texture periodicity.Analysis is also conducted to the terrain texture complexity through angular second moment parameters computed by hillshade data.Eigenvalue has clear peak value in the sample region of flat and the eigenvalue of platform decreases obviously.Eigenvalue of hills and mountain region verge to zero which shows that texture of plat has lowest complexity,followed by the lower complexity of platform and the highest complexity of hills and mountain region.This paper also proposed a multi-parameter integrated method which employs both comprehensive periodicity and comprehensive complexity in terrain texture quantitative analysis.This method not only reduces replicate analyses but also makes full use of various texture parameter information,it also unifies range through normalization for the convenience of quantitative analysis.The result showed that these two parameters have significant response to the different terrain texture,which shows a great potential in landform recognition and classification.

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[87]
Liu P J, Zhu Q K, Wu D Let al., 2006. Automated extraction of shoulder line of valleys based on flow paths from grid Digital Elevation Model (DEM) data.Journal of Beijing Forestry University, 28(4): 72-76. (in Chinese)The extraction of a continuous shoulder line of valleys with a precise location is a critical technique in constructing the mechanism-process models of spatial distribution, such as those for soil erosion, sediment transportation and runoff process in gully areas of the Loess Plateau. The extraction technique presented in this paper is based on a hydrological method of river network and catchment boundary extraction, utilizing slope variation of a flow path to define the feature segment of slope profile and produce a continuous shoulder line of valleys. In this paper, the authors presented an algorithm, by which the drainage network and the continuous shoulder line of valleys were extracted automatically from the DEM of Caijiachuan watershed in Jixian County,Shanxi Province, which is located in the gully area of the Loess Plateau. The final result agrees with the optical interpretation from slope distribution in the experimental area.

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[88]
Liu R J, Zhu H C, Tang G A et al., 2012A. Study of potential factor for water erosion on loess hillslope based on DEMs.Bulletin of Soil and Water Conservation, 32(5): 161-165. (in Chinese)The earth surface erosion by runoff is essentially a result from gravitational potential energy of running water.Started with energy accumulation of slope running water,basic concepts and computational principles of the potential factor for running water erosion reflecting erosive power of original slope were presented.Algorithm of the computation for the potential factor was designed based on the high precision DEM,computation of the potential factor was completed for a simulated multiphase watershed,and the result corresponding to erodent power points was acquired based on the potential factor.The spatial distribution characteristics of erosive power points were analyzed and then,some preliminary discussions on the evolution of topography were made.Results showed that the research on slope erosion degree and its evolution in use of the potential factor is of theoretical significance and practical value.

[89]
Liu S C, Zhang W C, Gao M Fet al., 2007. Simulation of land surface evapotraspiration using distributed hydro- logical model, remote sensing and GIS technology.Scientia Geographica Sinica, 27(3): 354-358. (in Chinese)Evapotranspiration(ET) is the key factor to the research on water circulation and heat balance in the soil-vegetation-atmosphere system.In this article,a pixel based adapted DHSVM distributed hydrological model that integrates remote sensing and geographic information system was applied in the Ziwuhe River watershed in the upper Hanjiang River basin.The modeled pixel is 60 m large.Our study focused on the atmospheric and topographic correction on optical remote sensing data and utilizing 30 m resolution Landsat TM data to obtain leaf area index and the land use and land cover data.Some useful terrain factors as slope and aspect and topographic index could also be derived from digital elevation model.The results showed that the spatial pattern of ET was similarity in different temporal scales,moreover,it was found that daily ET spatial differences were more evident.The result also showed that the distributed model could be used in small basin of humid climate.

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[90]
Liu T, Zhao J M, Gong D Het al., 2013. Energy accumulation based method for stream knickpoints extraction.Groundwater, 35(6): 159-160. (in Chinese)

[91]
Liu X J, Gong J Y, 2001. Delaunay triangulation of constrained data set.Acta Geodaetica et Cartographica Sinica, 30(1): 82-88. (in Chinese)The triangulation of constrained data set is widely used in Geographic Information System(GIS),geo-science,computational geometry,multi-resolution and high precision DTM, et al. This paper researches the triangulation of constrained data set and briefly analyses some existing algorithms. A new iterative algorithm and deleting algorithm for triangulating constrained data is proposed.

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[92]
Liu X J, Zhang P, Zhu Yet al., 2009. Suitable window size of terrain parameters derived from grid-based DEM.Acta Geodaetica et Cartographica Sinica, 38(3): 264-271. (in Chinese)The size of local moving window is one of the key factors when slope is derived from grid based DEM.In the paper,slope accuracy model based on the size of DEM local moving window is firstly presented and a methodology to evaluate quantitatively the loss of topographic detail is proposed through a χ2-test of the corrected residuals in immediate neighborhood of the evaluation point.Then based on samples of different terrain positions at selected test area,this paper discusses the effect of the size of local window on slope accuracy and analyzes the match of the fitness surface and DEM terrain surface.Lastly,this paper provides a suitable size of window for deriving slope based on grid DEM.The results of the research show that:① the slope accuracy can be increased with increasing the size of evaluation window;② the comparability of the fitness and DEM terrain surface is lowered when the size of window is become larger;③ under the condition of the fitness matching the DEM terrain surface,the slope accuracy can be improved through enlarging the window size and 5×5 local moving window is suggested for calculating DEM slope;④ attention should be paid to the shape of the fitness surface that can be really described the DEM surface in terrain analysis based on DEM,otherwise the results of terrain parameters,such as slope,aspect and curvatures,are only provided with mathematical meanings and can not express the terrain features of DEM.

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[93]
Liu Y, Wang Y X, Pan B T, 1999. A preliminary approach on the 3D presentation and quantitative analysis of planation surface.Geographical Research, 18(4): 391-399. (in Chinese)Planation Surface is one of the very important issues in the field of current geomorphology, and plays a major role for reconstructing the evolutional history of land from in a region. By using remote sensing and geographical information systems, this article discussed the creation of the Digital Elevation Model (DEM) of the Meiwu Plateau, at the south of Lanzhou and the northeastern margin of the Qinghai-Xizang Plateau, and the integration of both DEM and Landsat TM images. Then the characteristics of 3D Geomorphological Imagery of the Meiwu Plateau were discussed, and the topographic profiles at several parts of the DEM were got. On the basis of analyzing the system of geomorphological parameters on the planation surface, the exact extent of the planation surface on the Meiwu Plateau was got by using the supervised classification technique in the field of image processing. The great potential of this technique was discovered on the analysis of planation.

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[94]
Liu Z P, He H J, Zhu F H, 2009. Study of technology of fast 3D modeling and visualization based on borehole data.Rock and Soil Mechanics, 30(Suppl.1): 260-266. (in Chinese)For the purpose of intellectualization and automation in the process of 3D modeling and also for simplification of complex geological body modeling,DXF interface program which can read the borehole data and some other drawing data from CAD and rewrite it to database or visualize it is programmed.The 3D fast modeling method is put up with,which dose the interpolation with stratus attribute values by means of GA-Kriging.Moreover,the functions including modeling,contours drawing,display of boreholes,slicing of strata,extraction of special stratum,calculation of volume and so on.In the programming of Kriging interpolation method code,the GA intelligent algorithm is applied for the calculation of constant parameters such as nugget constant and range.It is proved that in this way global optimal solution of the parameters can be obtained easily.Finally,an engineering instance is given to test whether this kind of modeling method and related program codes are appropriate or not;it is shown that in this way the 3D modeling becomes easy and efficient.

[95]
Liu Z Y, Zhang X, Fang R H, 2010. Analysis of spatial interpolation methods to precipitation in Yulin based on DEM. Journal of Northwest A&F University (Nat. Sci. Ed.), 38(7): 227-234. (in Chinese)

[96]
Long E, Cheng W M, Xiao Fet al., 2007. Extraction of landform information in Changbai Mountains based on SSRTM-DEM and TM data.Journal of Mountain Science, 25(5): 557-565. (in Chinese)

[97]
Long S C, Liu W B, Lin Jet al., 2011. Improvement in DEM and DLG of JieXi4 Digital Photogrammetry System.Bulletin of Surveying and Mapping, 2: 12-16. (in Chinese)

[98]
Luo M L, 2008. Research on terrain feature point cluster based on DEMs [D]. Chengdu: The Graduate University of Chinese Academy of Sciences. (in Chinese)

[99]
Luo Y X, Su B L, Zhang Qet al., 2013. Identifying and modeling confined hydrological processes in plain polders.Resources Science, 35(3): 594-600. (in Chinese)The plain polders are characterized by flat topography,low hydraulic gradients,and controlled hydrological processes.Hydrological connection between the inside polder area and the receiving water body is confined by the water control facilities.The plain polders are often highly regulated,which may change and add up to the complexity of hydrological processes such as production and concentration.SWAT is a physically based,distributed model,which can simulate rain-runoff process,sediment and nutrient transport in watersheds with complex land use,soil and management.However,hydrological processes are usually modeled as free discharge processes,which is not applicable in plain polders.In addition,watershed delineation cannot be simply accomplished without considering anthropogenic land cover features(i.e.dykes,sluices,and roads),which will affect runoff processes.As the dykes and sluices segment the whole polder into several independent catchment units,it is proposed to model the hydrological processes separately for each catchment unit,which makes the modeled process agree with the real routing process affected by dykes.As runoff is usually routed through the ditches to the nearby pumping station and pumped out under control,it is proposed to model the hydrologic processes with multiple outlets,which can make the modeled process agree with the realistic one.River network and anthropogenic land cover features(i.e.dykes,sluices,and roads)were incorporated into the DEM to make the watershed delineation agree with the realistic flow direction and accumulation process.The reservoir,which acts as the impoundment of pump station,was added to model the confined drainage processes.The results show that these watershed delineation techniques can simulate the manually-controlled and complicated hydrological processes in plain polders.Scenario analysis showed that the outflow of confined process was slightly lower than the free-discharge process under the same conditions,indicating the retention effect of runoff in the pump station.The water body of the pump station can store runoff until water exceeds the target volume.During this process,the hydrologic residue time is increased compared to the free-discharge process,increasing the time of water-lose processes such as infiltration and evaporation.After adding a reservoir to control the drainage process,there is little or no outflow in the confined process during the dry season,in accordance with the observed drainage process.

[100]
Lv G N, Qian Y D, Chen Z M, 1998. Study of automated extraction of shoulder line of valley from grid digital elevation data. Scientia Geographica Sinica, 18(6): 567-573. (in Chinese)The extraction of continuous shoulder line of valley having precise location is the key technique to the construction of spatial distribution mechanism-course models such as soil erosion, sediment transportation and runoff course in gully area in the Loess Plateau. The extraction technique presented in this paper is a morphologically based method utilizing finite morphologic elements to define the topographical structure. In this paper, the authors present an algorithm by which the drainage network and the continuous shoulder line of valley is extracted automatically from the DEM of Wangjiagou in Lishi, Shanxi, which is located in gully area in the Loess Plateau, and the final result is in accordance with the real condition of the experiment area.

[101]
Lv Y, 1981. Research of polyhedral function in digital elevation model.Geomatics and Information Science of Wuhan University, 2: 14-27. (in Chinese)

[102]
Ma H B, Guo J T, 2007. Study on facial-volumetric mixed 3D geological modeling based on sections.Metal Mine, 372(7): 50-52. (in Chinese)3D geological modeling and visualization is a key technique in digital mine and is of great importance to the mine production, geoscienctific analysis and resource assessment.With the drill-hole information and geological section map as the basic data, the paper proposes a section-based 3D geological modeling process, which is used to establish the facial model of the geological body and the volumetric model of its corresponding geological blocks so as to finally realize a “section-TIN-block” facial-volumetric mixed modeling and visualization of the scientific calculation.The key algorithm involved in the modeling is studied; the method “cut-and-sew” is proposed for solving the 3D reconstruction problem of adjacent section contour lines which are greatly different from each other in the number of the shape and vertex; and the triangulation algorithm for polygon with islets is studied for solving the modeling of complex geological body with stones and holes.

[103]
Ma L B, Cao X S, 2008. A computing method of spatial accessibility based on Heuristic A* algorithms and grids partition.Geographical Research, 27(1): 93-99. (in Chinese)An accessibility computing method based on grid partition and heuristic A* searching algorithms was put forward in the paper,which is used to research accessibility spatial distribution feature in the study area through computing each grid's accessibility. Traffic cost is an important element in accessibility computing.There are two approaches to stimulate grid traffic cost,one is approach of density of road network,and the other one is approach of relative spatial resistance for different land use status.The density of road network is anti-correlative with traffic cost.Land use has a close relationship with urban traffic,so grid relative traffic cost can be stimulated directly by integrating the two approaches,actual status of road and topological structure of road network was ignored.A computing formula of grid relative traffic cost was defined in the paper. The key point is how to compute traffic cost of grids path.Dijkstra algorithm makes sure to get the lowest traffic cost,but it must spend more searching space and time.Not only can A* algorithms improve searching efficiency,but also can add some heuristic searching information to make searching result more reasonable.The key of the searching process is the definition of heuristic evaluation function H,which is responsible for estimating traffic cost from intermediate grid to target grid.Usually,marching from one spot to another is constrained by two factors: distance and arrival angle.So Euclid distance and marching arrival angle are adopted to evaluate traffic cost.In application,in order to make computing result accorded with practice,more heuristic information can be imported into computing process. For verifying our research,a software package was developed with C# language under ArcEngine9 environment.A case study was implemented by using the package.Accessibility of business districts was selected as computing object in Guangzhou city.The computing result by using the method can provide a quantitative reference for urban planning of the city.

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[104]
Ma R A, Yang J Y, Wang H Y, 2003. Volume rendering model and algorithm applied to seismic data visualization.Computer Engineering and Applications, 39(22): 226-228. (in Chinese)Varying-density emitter model is applied to the analysis of petroleum-gas's location and reserves according to features of seismic data.Then the location of well can be decided more precisely.The traditional ray-tracing algorithm is improved,the ray and voxel cube are converted discretely,the data fields are scanned by the layer-based way.Since these the time of rendering and memory are decreasing steeply.

[105]
Meng D Y, Lu Y Q, Li X Jet al., 2014. Impact of expressway network construction on the regional accessibility in the Yangtze River Delta.Tropical Geography, 34(5): 643-654. (in Chinese)The basic spatial economic efficiency of expressway network construction is to shorten regional travel mileage and travel time, which will be propitious to improve the regional traffic accessibility level and strengthen regional socio-economic linkage. Since the 1990s, the expressway in the Yangtze River Delta has experienced initial development stage, linear expansion stage, network construction stage and network promotion stage. With the large-scale construction of expressway infrastructure, the regional expressway network scale has been expanded significantly, the network connection degree has been improved and the network structure has been optimized continuously, whose direct spatial economic effect is to promote spatial-temporal accessibility in the Yangtze River Delta. In the paper, the Yangtze River Delta is taken as a research scope, the spatial-temporal accessibility level and changes are calculated and compared by the model of node average traffic mileage, node average circuitous coefficient, node average travel time and regional average travel time, based on the database of highway network in the Yangtze River Delta in 1992, 1998, 2004 and 2010. The results show that: 1) Average traffic mileage of each county has been shortened, and the average circuitous coefficient has also reduced greatly, but the variation range disparity is remarkable in different development stages and among different counties, especially, the variation range of node average traffic mileage in the third stage (2004-2010) was the greatest among the three stages, and the variation range of node average circuitous coefficient of the counties along the Yangtze River and Hangzhou Bay was greater than that of the others because of the construction of Suzhou-Nantong Yangtze Road Bridge and Hangzhou Bay Bridge. 2) The node average travel time and the regional average travel time also got a great promotion under the construction of expressway in the Yangtze River Delta, especially in the outlying district of the Yangtze River Delta, while the variation range of node average travel time and regional average travel time would be decreased under the limitation of diminishing marginal returns of highway network construction. Through the comparison of spatial-temporal accessibility and its promotion in different development stages in the Yangtze River Delta, the necessity and significance of expressway construction are objectively demonstrated, which can be in favor of providing the theoretical reference for the transportation network optimization and regional development strategy formulation.

[106]
Miao L L, Fang C Y, Pan Y Jet al., 2015. The entirely accessibility analysis of highway network in Jinggangshan Scenic Region.Economic Geography, 35(3): 178-184. (in Chinese)

[107]
Ming J, Pan M, Qu H Get al., 2008. Three-dimensional geological multi-body modeling from netlike cross-sections with topology.Chinese Journal of Geotechnical Engineering, 30(9): 1376-1382. (in Chinese)To overcome the limits of traditional modeling methods using parallel and planar cross-sections,a new multi-body modeling method was put forward.The netlike cross-sections with the topological relationship of "node-arc-polygon" were utilized.The resulted models,without voids and overlapping,could also be smoothened all together.During the modeling process,the target area was subdivided into several cross-section grids,which could be modeled independently.All the sub-models in each grid were merged to build the final resulted models.Eight geological models in city geology survey were successfully constructed by using real data in Beijing,and the capacity of the method to quickly and exactly simulate large area with complex geological phenomena was demonstrated.

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[108]
Mo S G, Zhang B P, 2007. Simulation of temperature fields based on DEM in Qinling Mts.Journal of Mountain Science, 25(4): 406-411. (in Chinese)Qinling Mts.,middle-altitude mountains in central China,is an important climate borderline of the North and the South in China.Many climate simulation methods based on terrain are studied to simulate mountain climate fields by former researchers and can help to temperature fields' simulation of Qinling Mts.Considering the influent factor of landforms on temperature fields and the aspect differences on northern and southern slopes alone the ridge of Qinling Mts.,the DEM-Aided spatial interpolation method is applied on the basis of Ordinary Kriging interpolation method and the temperature fields of Qinling Mts.are simulated.Based on the data of meteorological observation stations and the DEM data with the grid precision of 100 100 meters,this paper simulates the temperature fields of Qinling Mts.by GIS spatial analysis methods,and the cross validation is adopted to simulation results.The report indicates that the simulation results of temperature fields of Qinling Mts.based on DEM are perfect,the prediction errors precision are rational,and the results reflect accurately the temperature distribution features of Qinling Mts.,which indicates that Qinling Mts.is an important climate borderline in China.At the same time,the simulation of temperature fields has proved that Qinling Mts.has evident climate differentiational and climate effects on both sides of Qinling Mts.

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[109]
Mo Z N, 2001. Analysis on the hydrological characteristics and water stage forecasting of the diked area.Journal of China Hydrology, 21(4): 35-37 (in Chinese)

[110]
Pan J H, Liu Y, 2014. Measurements for spatial field of cities at prefecture level or above in China based on ac- cessibility and field-strength model.Human Geography, 29(1): 80-88.

[111]
Pan J H, Liu Y, 2014. Measurements for spatial field of cities at prefecture level or above in China based on accessibility and field-strength model.Human Geography, 29(1): 80-88. (in Chinese)Spatial filed is an abstract concept to define the potential difference came from the process of the growth pole of regional economy driving the economic development of periphery areas through transport corridors. In this paper, complex components for calculating the urban nodality index are selected, with consideration to the following five specific aspects, i.e., economic development, social progress, science education, resources infrastructure and ecological environment conditions. With the application of raster cost weighted distance method,k-order data fields and EADA(Exploratory Spatial Data Analysis),this paper attempts to comprehensively measure the regional accessibility and the spatial field of cities at prefecture level or above in China,and to reveal the spatio-temporal characteristics of macro disparities,the three zones and the economic disparities in the Northern-Southern China from inter-province,inter-city,inter-county. The results indicate that the accessibility condition continues to be improved and the average accessibility is min and 193.43 in 1991 and 2010 respectively,increase by 53.55min. Moreover,spatial filed have been increasing significantly from 1991 to 2010,while the economic disparities are different at different research scales. The distribution pattern of spatial field appears to be single-core form in 1991,while that in 2010 tends to be "multi-polar"network form. The differences between the Southern and Northern China evolves from"South and North are in balance"to"South is stronger than North".. On the basis of measurement and analysis for urban spatial filed,a two-level zoning project of urban economic regions of the whole country is put forward.

[112]
Pan Y Z, Gong D Y, Deng Let al., 2004. Smart distance searching-based and DEM-informed interpolation of surface air temperature in China.Acta Geographica Sinica, 6(3): 366-374. (in Chinese)Statistical interpolation of the temperature for the missing points is one of the most popular approaches for generating high spatial resolution data sets. However, many interpolation methods used by previous studies are purely mathematic ways, without geographical significance being considered. In the present study the authors interpolate the monthly and annual mean temperature climatologies using 726-station observations in China, utilizing improved methods by taking into account geographical factors such as latitude, longitude, altitude. In addition, a smart distance-searching technique is adopted, which helps select the optimum stations on which the guess values at missing points are generated. Results show that the methods used here have evident advantages over the previous approaches. The mean absolute err of ordinary inverse-distance-squared (IDS) technique is in the range of 1.44-1.63oC, on average 1.51oC. The smart distance searching technique yield a MAE of 0.53-0.92oC, on average 0.69oC. Errors have been reduced as much as 50%.

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[113]
Qin C Z, Yang L, Zhu A Xet al., 2006. Computation method of topographic wetness index in low relief area.Progress In Geography, 25(6): 87-93. (in Chinese)Topographic wetness index, which is designed for modeling the status ("dry" or "wet") of the soil moisture quantitatively, is an important index for both predictive soil mapping and distributed hydrological modeling in a catchment. Current methods for calculating topographic wetness index have evident problems when applied in low relief area. Outside the positions of narrow accumulation line with high topographic wetness index, the topographic wetness index dramatically jumps down in other parts of wide valley area. This is unreasonable because the soil moisture should be comparatively average and high in the wide and flat valley, and the value of topographic wetness index should be high. This problem is caused by both the flow accumulation algorithm and the slope gradient used during computing the topographic wetness index. A new method for computing topographic wetness index is proposed in this paper to address this problem. Firstly, flow accumulation is calculated by a multiple flow direction algorithm(MFD-fg). Topographic wetness index is then computed by the flow accumulation and maximum downslope. The maximum downslope used in the computation of topographic wetness index is matched with the idea of both MFD-fg and topographic wetness index. Furthermore, a post-processing method is also proposed to compute the topographic wetness index in valley area. The topographic wetness index in the valley area is interpolated by a Gaussian function based on the value of the topographic wetness index on the nearest position on extracted flow accumulation line. The application in a small watershed shows that the method proposed in this paper can get a comparatively reasonable distribution of topographic wetness index for not only the hillslope but also the wide valley area. The value of topographic wetness index in valley area is averagely high and with a smooth transition, which reflects the natural status of the soil moisture in application area. In the future research, the method proposed in this paper will be evaluated by both artificial surfaces and the real applications.

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[114]
Qin C Z, Zhu A X, Pei Tet al., 2007. An adaptive approach to selecting a flow-partition exponent for a multiple-flow-direction algorithm.International Journal of Geographical Information Science, 21(4): 443-458.中国科学院机构知识库(中国科学院机构知识库网格（CAS IR GRID）)以发展机构知识能力和知识管理能力为目标，快速实现对本机构知识资产的收集、长期保存、合理传播利用，积极建设对知识内容进行捕获、转化、传播、利用和审计的能力，逐步建设包括知识内容分析、关系分析和能力审计在内的知识服务能力，开展综合知识管理。

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[115]
Qiu L J, Zheng F L, Yin R Set al., 2012. Effects of DEM resolution and watershed subdivision on hydrological simulation in the Xingzihe watershed. Acta Ecologica Sinica, 32(12): 3754-3763. (in Chinese)The Soil and Water Assessment Tool(SWAT) is a watershed-based,semi-distributed hydrologic model that has become one of the most powerful tools for simulating hydrological processes at different spatial scales.The SWAT model utilizes geographic information systems and digital elevation model(DEM) to delineate watersheds and extract the stream network.The simulation accuracy depends on how well the model inputs describe the watershed.High resolution DEM generates more accurate topographic estimations,but such information is costly to obtain,especially in the hilly and gully region of China Loess Plateau.In addition,the size of the extracted subwatersheds strongly depends on the pre-selected threshold value of the watershed subdivision.The size and number of subwatersheds can also affect the watershed modeling process and subsequent results;however,there are no accepted guidelines for selecting the threshold value,making the extraction of subwatersheds a subjective process.Therefore,the objective of this study was to investigate the effect of DEM resolution and watershed subdivision on the simulation of hydrological processes at the outlet of the Xingzihe watershed in the hilly and gully region of the Loess Plateau.In our study,the digital filter method was used to separate base flow from the measured streamflow data at the Zhao n hydrological station from 1958 to 1974.The applicability of the SWAT model in the Xingzihe watershed was assessed on an annual basis.The impacts of DEM resolution and watershed subdivision on the simulation of annual streamflow,surface runoff,base flow,and sediment yield were evaluated by running the model with ten DEMs(20,30,60,90,150,300,500,1000,1500 and 2000 m) and seven threshold values(10,12,15,30,50,100 and 200 km2) for the watershed subdivision.The results showed that the SWAT model accurately simulated annual streamflow,surface runoff,base flow,and sediment yield in the Xingzihe watershed.DEMs with fine resolution(i.e.,20 to 150 m) were required to simultaneously simulate annual streamflow,surface runoff,base flow and sediment yield with a high degree of accuracy(R20.93,NSE0.51,RSR0.43).For DEM resolutions greater than 150 m,the accuracy of the simulation varied among the hydrologic elements.The threshold values of the watershed subdivision had little effect on streamflow,surface runoff and base flow.However,the threshold values had a large effect on sediment yield.Watershed subdivision threshold values of 12 to 100 km2 were required to adequately predict sediment yield.Threshold values less than 12 km2 or greater than 100 km2 led to the underestimation of sediment yield.These findings indicated that choices regarding the DEM resolution and threshold value of the watershed subdivision should be based on the hydrological element of interest.The SWAT model was limited in its ability to simultaneously simulate all of the hydrologic elements in the Xingzihe watershed at short time scales(i.e.,daily and monthly);therefore,this paper did not discuss the effects of DEM resolution and watershed subdivision threshold values under different time scales.Additional research is needed to ascertain if the results will change when running the model at different time scales.

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[116]
Qiu X F, Zeng Y, Liu S M, 2005. Distributed modeling of extraterrestrial solar radiation over rugged terrains.Chinese Journal of Geophysics, 48(5): 1028-1033. (in Chinese)Based on DEM (digital elevation model) data, a distributed model for calculating extraterrestrial solar radiation (ESR) over rugged terrains is developed. This model gives an all-sided consideration on factors influencing ESR. Besides, the proposed model taking the DEM data as input has ability to process mass of data and is applicable to satellite image processing platforms or GIS (Geographic Information System). Using DEM data as the general characterization of terrains, ESR quantity with resolution of 1 km 1 km for the rugged terrains of China is calculated. The results suggest that the annual ESR quantity has clear latitude-dependent variation characteristics and a progressive increase trend from north to south. The annual ESR quantity azonal distribution characteristics appear in mountainous areas owing to the effects of topographical factors such as aspect, slope and terrain inter-shielding. The calculated ESR of China in this work can be employed as basic geographic data for relevant studies.

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[117]
Ren L L, Liu X R, 2000. Hydrological process modeling based on digital elevation model.Geographical Research, 19(4): 369-376. (in Chinese)The Digital Elevation Drainage Network Model (DEDNM) of the Shiguanhe River catchment is made from digital elevation model by Martz and Garbrecht method with spatial basin heterogeneity considered. Subwatershed, drainage network, and their spatial topological relations are generated automatically by computer. Then, spatial cumulative distribution probability of topographical index ln( a /tg ) i in the TOPMODEL is calculated. Therefore the parabolic exponent of soil tension water storage capacity distribution within each subwatershed in the Xin'anjiang model can be obtained by dimensionless processing with respect to cumulative distribution curve of ln( a /tg ) i . That makes the parabolic exponent in the Xin'anjiang model be physically based. Finally, the digital hydrological model is established. The case study on the Shiguanhe River catchment in the Huaihe River Basin, i.e., the intensified observation field of GEWEX Asian Monsoon Experiment Project, showed that the digital model performs very well not only in simulating runoff processes at any specific outlet, but also in simulating spatial distribution and temporal variation of hydrological elements and state variables (especially soil moisture), if compared with traditional hydrological models. That provides solid foundation for making full use of present observation information and thorough tapping potentials of hydrological data.

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[118]
Shen J H, Lu Y Q, Lan X Jet al., 2012. Assessment on accessibility of regional comprehensive transport: A case study of Anhui.Geographical Research, 31(7): 1280-1293. (in Chinese)The authors evaluate the provincial accessibility,county accessibility,opening accessibility between adjoining districts,two fare costs and probability of attraction based on social and economic factors of districts in Anhui Province,point out spatial accessibility structure of diversified indexes of towns in this province,and build a model of comprehensive accessibility indexes,and achieve spatial structure of comprehensive accessibility of the towns.We find that spatial pattern of the towns in Anhui is taking Hefei as the center and extending toward edge by and large,but the spatial pattern does not constitute regular concentric circles;county analysis reflects distinct differences between south towns and north towns.Accessibility of south and southwest towns is bad and good in the north towns,respectively;the towns are identified as severe shrinkage,sharp expansion,substantial stabilization and fluctuation in the opening analysis;spatial structure of fare cost based on the shortest line forms circularities centered embayment towards northeast;analysis of the least fare cost testifies spatial structure of accessibility of the towns following with extension of railway network;attractive indexes of probability indicate that the towns with high attractive indexes of probability present a shape of "?";comprehensive accessibility indexes of the towns reveal symmetry between north and south in Anhui,but the pattern is broken by mountains of South Anhui.In the end,the researchers offer some proposals on some flaws of road network: promote new regional growth poles in north central Anhui for further strengthening their internal relations;accelerate the construction of high-grade highways in Huaibei plain,in particular strengthen lateral ties between the towns of North Jiangsu and South Henan provinces;extend connectivity of high grade roads in the northern and southern parts of Maanshan;improve the road facilities of the Wanjiang City Belt.

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[119]
Song X D, Tang G A, Li F Yet al., 2013. Extraction of loess shoulder-line based on the parallel GVF snake model in the loess hilly area of China.Computers & Geosciences, 52(1): 11-20.Loess shoulder-lines are the most critical terrain feature in representing and modeling the landforms of the Loess Plateau of China. Existing algorithms usually fail in obtaining a continuous shoulder-line for complicated surface, DEM quality and algorithm limitation. This paper proposes a new method, by which gradient vector flow (GVF) snake model is employed to generate an integrated contour which could connect the discontinuous fragments of shoulder-line. Moreover, a new criterion for the selection of initial seeds is created for the snake model, which takes the value of median smoothing of the local neighborhood regions. By doing this, we can extract the adjacent boundary of loess positive egative terrains from the shoulder-line zones, which build a basis to found the real shoulder-lines by the gradient vector flow. However, the computational burden of this method remains heavy for large DEM dataset. In this study, a parallel computing scheme of the cluster for automatic shoulder-line extraction is proposed and implemented with a parallel GVF snake model. After analyzing the principle of the method, the paper develops an effective parallel algorithm integrating both single program multiple data (SPMD) and master/slave (M/S) programming modes. Based on domain decomposition of DEM data, each partition is decomposed regularly and calculated simultaneously. The experimental results on different DEM datasets indicate that parallel programming can achieve the main objective of distinctly reducing execution time without losing accuracy compared with the sequential model. The hybrid algorithm in this study achieves a mean shoulder-line offset of 15.8 m, a quite satisfied result in both accuracy and efficiency compared with published extraction methods.

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[120]
Song Z Y, Yan Y X, Xue H Cet al., 1998. Study on the development of hydrodynamic mechanism of the radiation sandbar in the South Yellow Sea: II. The facade features of tidal movement. Science in China (Series D), 28(5): 411-41728-34. (in Chinese)

[121]
Sun C B, Xie X S, Jiang W L, 2012. Distribution of the knickpoints in fluvial gullies in response to the events of Holocene fault activity: A case study of the Jiaocheng fault in Shanxi.Seismology and Geology, 34(2): 254-267. (in Chinese)Jiaocheng Fault zone is located in central Shanxi downfaulted system,and controlls the western margin of the Jinzhong Basin. It starts at Nitun town,Yangqu County in the north and ends to the west of Fenyang city in the south,about 125km long,striking NE and dipping SE.Based on the survey and research of 41 gullies and 124 knickpoints along Jiaocheng Fault zone,this paper discusses the distribution characteristics of knickpoints of the gullies along Jiaocheng Fault zone: ①The number of knickpoint series of upstream gully is positively proportional to the length of upstream gully; ②The distance of knickpoints is positively proportional to the length of the gully in each class knickpoints.③The distance of different class knickpoints is close to equal in about 1/3 gullies,and it reflects equal interval in time of the fault activity with vertical displacement; ④Bedrock knickpoints and knickpoints in loose sediments have commonness,there isn't obvious difference between them; ⑤ 1～5m high knickpoints accounted for 72%of the total 124 knickpoints in the survey area,the height of the main knickpoints reflects the vertical displacement of the fault activity; ⑥With the comparison of the paleoearthquake events revealed by the excavation of trenches along the fault zone,the latest first,second,third class knickpoints in survey area are corresponding with three faulting events occurring respectively 3.06～3.74ka,5.91ka and 8.53～8.56ka BP; ⑦taking the time of the paleoearthquake events as a reference,the headward erosion rates of the first knickpoints of a-d grade gullies are 0.6～0.7cm/yr,2.7～3.3cm/yr,5.6～6.8cm/yr and 8.4～10.2cm/yr,respectively. The rates of the second class knickpoints of b-d grade gullies are 2.6cm/yr,4.6cm/yr and 8.4cm/yr,respectively; and ⑧ the average heights of the 3 events are 2.8m,3.0m and 2.6m,respectively,which match the dislocations of the 3 paleoearthquake events revealed by previous trenches. Some factors which may influence knickpoint series and knickpoint distance in the investigation of knickpoint are discussed in the end.

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[122]
Sun J L, 2011. Research on the loess slope-landscape structure based on DEM: Case study in Shanbei Loess Pla- teau [D]. Nanjing: Nanjing Normal University. (in Chinese)

[123]
Sun Z R, Yin H W, Kong F H, 2012. Study on different calculation methods of park accessibility.China Popula- tion Resources and Environment, 22(5): 162-165. (in Chinese)A city park' s spatial layout represents the justice of social equity,subsequently influencing its social and ecological function. In this paper,a mechanism model and its calculation method of accessibility were deeply discussed.The results show that:①Network analysis,based on road network more accurately assesses accessibility of urban parks;(2) Jinan city is in lack of urban parks, only about one in fifth of the residents can use parks conveniently,and there is a remarkable distance in park area per capita compared to international cites;③spatial distribution of urban parks is uneven:Shizhong district has a better accessibility,the urban area is better than the surrounding area,and accessibility shows a trend of weaking from downtown to the outside.

[124]
Tang G A, 2014. Progress of DEM and digital terrain analysis in China. Acta Geographica Sinica, 69(9): 1305-1325. (in Chinese)Digital elevation model (DEM) is known to be one of the most important national fundamental geographic information data. The theory, method and application of digital terrain analysis (DTA) based on GIS is a hot research issue in geography, especially in the field of geographical information science. This paper makes an overall review on Chinese scholars contribution to the research of DEM and DTA, especially to DEM data model, uncertainty, analysis method, scaling effect and high performance computing method, as well as its application in DTA. A few research groups in this field have made great progress recently, and young scholars are playing a critical role in the process. Their research has caught up with the international forefront, and achieved fruitful results in significant innovation. Some research, like DEM based regional geomorphological research on the Loess Plateau and Tibetan Plateau of China highlighted the contribution of Chinese scientists, which have had influence in the international academia to a certain degree.

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[125]
Tang G A, Li F Y, Liu X Jet al., 2008. Research on the slope spectrum of the Loess Plateau.Science in China Series E: Technological Sciences, 51(1): 175-185. (in Chinese)

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[126]
Tang G A, Liu X J, Lv G N, 2005. Principle and Methodology of Digital Elevation Model and Its Geo-analysis. Beijing: Science Press. (in Chinese)

[127]
Tao Y, Tang G A, Wang Cet al., 2010. Uncertainty of terrain information content based on grid DEM.Scientia Geographica Sinica, 30(3): 398-402. (in Chinese)Precision of DEM terrain information content is a key factor to judge the applicability and limit of DEM data.An experiment is designed to find out the effect of DEM subset partition strategy and number of subsets to the estimate precision of DEM terrain information content based on DEM,slope and aspect data of hilly and gully test areas on the Loess Plateau.The result shows that DEM terrain information content is affected by both terrain information and subset partition strategy.To weaken the uncertainty of DEM terrain information content calculated by traditional algorithms,this paper presents a DEM subset partition model based on the maximum entropy theorem.It provides an objective theoretical basis for DEM information content calculation and has been proved efficient to avoid the subjectivity and arbitrariness in DEM artificial classification.

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[128]
Tao Y, Tang G A, Wang C, 2011. Assessment on surface roughness models based on semantics and profile char- acteristics matching.Geographical Research, 30(6): 1066-1076. (in Chinese)As an important terrain factor,surface roughness calculated by digital elevation models(DEM) is directly used in geoscience models such as soil erosion models,surface photo-thermal simulation and so on.But there has been no generally accepted definition of surface roughness until now.Various types and similar concepts of surface roughness may cause difficulty for selecting a suitable surface roughness model.In this paper,we present a new algorithm for assessing surface roughness models based on semantics and profile characteristics.Some contrast experiments are presented by choosing hybrid landform types as sample areas,using DEM produced by traditional topographic map digitizing and LiDAR technology.Main conclusions are drawn as follows: (1) The method we presented in this paper can accurately express the local variation of terrain profiles suitable for assessing surface roughness models.(2) Both triangular boundary effect of TIN model generated by traditional contour based DEM production and surface random noise in DEM generated by LiDAR technology based DEM production influence the calculation of surface roughness.DEM data should firstly be filtered and noise reduced beforehand.(3) An SAR model is insensitive to the flat relief.It is not suitable for areas of plain and valley plain dominated areas.Roughness models based on vector calculus are accurate in expressing ridge and valley lines and straight slope areas which is not effectively described by SAR models.SDev model is more suitable for application in fine scale DEM.Slope based standard deviation model can be applied to most types of terrain,which is sensitive to four semantic rules.But SDsp model is more sensitive to break of slope.Curvature based standard deviation models are not advantageous in surface roughness description except for their high sensitivity in surface roughness of flat relief areas.

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[129]
Tian Y, Xiang Y, Gao Fet al., 2013. Automatic and fast 3D true city production based on pictometry oblique pho- togrammetry technology.Bulletin of Surveying and Mapping, (2): 59-63. (in Chinese)

[130]
Wan M, Xiong L H, Dong L H, 2010. Grid DEM-based distribution hydrological modeling for Feilaixia Water- shed.Engineering Journal of Wuhan University, 43(5): 549-553. (in Chinese)A grid digital elevation model(DEM)-based distributed watershed hydrological model which can utilize the watershed terrain characteristics represented by DEM,and take into account the asymmetry and the spatial scale coupling of the underlying surface,has become a hotspot in current hydrological model research.Taking Feilaixia reservoir basin with a catchment area of 34 097km2 for example,the SRTM 90m DEM data are used for extracting terrain characteristics information and delineating drainage networks and subwatershed;and a grid DEM-based distributed hydrological model is used to calculate the runoff in each DEM grid.Muskingum model is applied to channel flow routing and SCE-UA optimization algorithm is employed for parameters calibration and validation.It is shown that a grid DEM-based distributed hydrological model with simple structure,physical process and less parameters can be used to modeling the hydrological processes in the basin so as to achieve the better use of watershed terrain characteristics information and hydrological processes understanding.

[131]
Wang C, Tang G A, Liu X Jet al., 2009. The model of terrain features preserved in grid DEM.Geomatics and Information Science of Wuhan University, 34(10): 1149-1154. (in Chinese)A new DEM which is called features preserved Grid Digital Elevation(F-DEM) is proposed in this paper.The F-DEM is based on the "Vectorizing simulation and rasterizing organization" method and combines characteristics both of the terrain the physical objects by applying the object-oriented technology.Through abstractly describing terrain characteristics based on their morphology and seamlessly embedding terrain features information into general grid data with segmentation technology,F-DEMs not only can maintain the structural integrity of grid DEM,overcome the disadvantage of imprecision terrain description in some places containing break terrain features,but also can keep its efficiency of terrain simulation with preserved features,which is of critical significance to research high-fidelity DEMs.

[132]
Wang C, Teng Y H, 2010. Design and application of integrated raster and vector data structure.Computer Engi- neering, 36(20): 88-89. (in Chinese)In the process of integrating "3S",the choice of a favorable data structure is the key point.This paper analyzes the advantages and disadvantages of both vector and raster data structures,and builds an optimal data structure based on the secondary dividing strategy,which merges the advantage of simultaneity vector and raster and can fulfill the requirement of vector data accuracy.It gives a logical representation of this data structure,and rasterizes the space data simultaneity.Based on that,it discusses the strategy of the collection and overlay analysis of space data based on this data structure.

[133]
Wang J C, 2015. Airborne LiDAR and photogrammetry matching application technology in the production of DEM.Geomatics & Spatial Information Technology, 5: 128-129. (in Chinese)

[134]
Wang J Y, Cui T J, Miao G Q, 2004. Digital elevation model and data structure.Hydrographic Surveying and Charting, 24(13): 1-4. (in Chinese)The article introduced the presentation and the application of DTM.It also presented the concept of DTM,DEM and DGM and the differences and relationship of them.The article discussed the data structure of the discrete points,the irregular triangles,the contour lines,profile lines and the regular grids,and compared the characters of the different data structures.

[135]
Wang L L, Li Z J, Bao H J, 2007. Application of hydrological models based on DEM in the Yihe Basin. Journal of Hydraulic Engineering, S1: 417-422. (in Chinese)The GIS technology and DEM-based watered information extracting methods are used to improve the Xinanjiang model and TOPMODEL.The new Xinanjiang model based on DEM grid,named Grid-Xinanjiang model,and the new TOPMODEL based on DEM grid,named GTOPMODEL are established.The models are applied to simulate the process of hydrology in Yihe basin.By watered information extracting,calibrating parameters and simulating flood processes,the suitability of GIS and DEM technology and corresponding models are investigated.The result shows that all these four models can well simulate the process of hydrology in Yihe basin.Among them the Grid-Xinanjiang model and GTOPMODEL based on DEM grid is better.

[136]
Wang L, Tang G A, Liu X Jet al., 2004. Terrain complexity index and its derivation from DEMs.Bulletin of Soil and Water Conservation, 24(4): 55-58. (in Chinese)Based on an overall analysis of the methodology and technique for the description of terrain information representation, the TCI(Terrain Complexity Index), a new concept and quantification method for terrain complexity is proposed. TCI is a comprehensive index revealing the complexity and variation of true surface, which could be extracted via a calculation of an angle between two conjunct surfaces from a 3 by 3 cells based analysis window. Experiments shows that the TCI matrix derived from 1 50 000 map scale DEMs could effectively represent the variation of the DEM based model surface. This research provides a good basis for constructing the conception system, as well as investigating the spatial distribution pattern of terrain information content.

[137]
Wang L, Yang Q K, Long Y Qet al., 2013. Determining DEMs’ resolution with digital photogrammetric data.Bulletin of Soil and Water Conservation, 33(5): 152-155. (in Chinese)

[138]
Wang M Z, Liu X J, Liu D, 2014. Unified computing method for camera calibration using multiple geometric constraints in single view. Bulletin of Surveying and Mapping,(2): 42-45, 79. (in Chinese)

[139]
Wang P, 2006. Study and application of non-point source pollution model of river network area based on digital basin system [D]. Nanjing: Hohai University, 2006. (in Chinese)

[140]
Wang W, Song Z Y, Lu W Get al., 2008. A theoretical analysis of the responses of coast tidal range to sea level rise.The Ocean Engineering, 26(3): 94-97. (in Chinese)Based on the analytical solution of the improved Taylor problem in the idealized semi-enclosed rectangular bay,the change of tidal amphidromic system of M2and coast tidal range with the sea level rise is studied in this paper.Schematizing the southern Yellow sea as an constant water depth and semi-enclosed rectangular bay,the evolution trends of tidal amphidromic system of M2and variation features of coast tidal range are analyzed primary under the condition of 3 and 5 meter rise of sea level respectively.The results show that with the sea level rise,amphidromic point in this sea area tends to move to the southeast,and then coastal tidal ranges change present consequently different features,that is,at the left side and bayhead coast near the amphidromic point they change evidently,and little at the right side and bayhead coast far away from amphidromic point.With the sea level rise in future,the result has value reference at the calculation of designing tide level in coast and ocean engineering.

[141]
Wang Y G, Zhu C Q, Wang Z W, 2008. A surface model of grid DEM based on coons surface.Acta Geodaetica et Cartographica Sinica, 37(2): 217-222. (in Chinese)Interpolation is the core problem of Digital Elevation Model(DEM).It influences every aspect in producing,quality controlling,accuracy evaluating,terrain analyzing of DEM.The main idea of current interpolation models is that interpolate the known values of some elevation points to get the unknown values of other elevation points.In grid,it is that construct the continuous surface by discrete values of some grid points to express the terrain surface.These models have big errors because of interpolating some points to get the whole surface.In this paper,the author constructs the Coons DEM model based on the approximation of topographical profile curve corresponding to the grid boundary curve interpolated by some adjoining grid points.For the constructing method,the model will change according to the topographical profile curve's change.As shown in experiment the Coons DEM model has high precision,its terrain simulation error is better than other DEM models' constructed with bilinear interpolation,spline function interpolation and moving surface fitting,and it reduces the terrain simulation error 15%~28% comparing with bilinear interpolation DEM model.By analyzing the Coons DEM model,the paper indicates that the models based on different boundary curves have different precision and the more grid points the boundary curves have,the higher precision the model has.At the end the reason why the Coons DEM model has high precision is analyzed in theory.

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[142]
Wang Y M, Guo M, 2012. A combined 2D and 3D spatial indexing of very large point-cloud data sets.Acta Geo- daetica et Cartographica Sinica, 41(8): 605-612. (in Chinese)A database management algorithm based on combined 2D and 3D indexing of very large point-cloud data is proposed,for extracting the point cloud in need and improving the query efficiency.Single-station point-cloud is managed with 2D quad tree and 3D MBB structure.Multi-station point-clouds are indexed with 3D-R tree.Finally the organized hierarchical model and other attribute data are stored in ralation-object database.The data storage,management and visualization of very large point-clouds are implimented on personal computer with massive point clouds from the ancient buildings such as Forbidden City.Result shows that the algorithm is able to manage more than 10 GB-level data and one billion effective points with satisfactory drawing efficiency.

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[143]
Wang Y M, Hu C M, 2012. A robust registration method for terrestrial LiDAR point clouds and texture image.Acta Geodaetica et Cartographica Sinica, 41(2): 266-272. (in Chinese)In order to get true and high resolution texture for terrestrial LiDAR point clouds,the photo should be taken to all directions.This will cause the large angle problem for the registration of point clouds and the texture image.Meanwhile,the error from control points and scanner also creates the low registration accuracy.A robust registration method is proposed to solve these problems.First,orientation element model of registration parameter is derived by the barycenter model of the space similarity transformation,normal rotation matrix and the antisymmetric matrix.The registration result is treated as initial value.Then,the high accuracy registration parameters are obtained by improved Danish iteration method with variable weights based on collinearity equation.Experiment shows that the new method is robust and accurate for the registration of any angle image and point clouds.

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[144]
Wang Y T, Chen X W, Bo Y Cet al., 2010. Monitoring glacier volume change based on multi-source DEM and multi-temporal remote sensing images.Journal of Glaciology and Geocryology, 1: 126-132. (in Chinese)

[145]
Wang Y, Xue S, Pan Met al., 2003. An automatic 3D vector data creation algorithm based on topology of section.Computer Engineering and Applications, 25(5): 1-2. (in Chinese)D vector data creation is a difficult problem in three-dimensional GIS research.This thesis imports the traditional topological relationship of2D GIS into section data and puts forward an automatic3D vector data creation algorithm based on topology of section data.Furthermore,it also suggests a method to solve the fault relative problems.

[146]
Wang Y, Zhu C Q, Shi W Z, 2000. Application of B Spline and smoothing spline on interpolating the DEM based on rectangular grid.Acta Geodaetica et Cartographica Sinica, 29(3): 240-244. (in Chinese)This paper studies the method and process of interpolating the DEM based on rectangular grid with B spline and smoothing spline. Comparing with dual linear interpolation an optimal spline algorithm is provided .Theoretical analysis and experiment indicate that the discussing methods have better effect.

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[147]
Wang Z G, Liu C M, Zuo Q Tet al., 2002. Methods of constructing distributed hydrological model based on DEM.Progress in Geography, 21(5): 430-439. (in Chinese)Resent advances in remote sensing, geographic information systems, and computer technology make the use of distributed hydrological model, based on digital elevation model (DEM), an attractive approach or tool to studying hydrological processes and evolution laws of water resources under changing environment. But distributed hydrological model is not perfect compared with lumped hydrological model. In order to promote its development, based on DEM, this paper discusses and sums up the characteristics of distributed hydrological model, then probes into two main ways and means of constructing distributed hydrological model. One way is like SHE model, another is like SWAT model. Although distributed hydrological models can be made in different ways, the primary structure of the model is quite similar. A typical structure of DEM based distributed hydrological model is provided in this paper. To better study the impact of the changing environment on hydrological processes, a watershed must be divided into subunits. This paper expressly discusses the three most common techniques used to discretize a watershed, which are respectively grid cell discretization, representative hillslope discretization and subwatershed discretization. In the final, as to the problem of constructing model, the methods of building the components of the distributed hydrological model is set forth from three aspects: input module, unit hydrology model and river routing model. A brief comment on the current distributed hydrological model research and some advice are given in the conclusion. All these will provide a guidance for making distributed hydrological model based on DEM.

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[148]
Wu L X, Chen X X, Che D Fet al., 2007. A GTP-based entity model for underground real 3D integral representa- tion.Geomatics and Information Science of Wuhan University, 32(4): 331-335. (in Chinese)Based on the amended and extended GTP model,the underground entity is extracted in levels of geosciences,geometry and topology,and eight geometric primitives including node,edge,arc,triangle,supper-surface,GTP,tetrahedron and super-body are abstracted.The arc refers to an unclosed curve comprised of two or more end-to-end edges,the supper-surface refers to a spatial surface represented by a group of triangles in order,and the supper-body is a spatial region enclosed by a few supper-surfaces or formed by a group of adjacent GTP elements.The geo-entity is 0-3D classified into point entity,line entity,face entity and body entity,and the body entity could be furthermore sorted as simple body entity,compound body entity and complex body entity.A GTP-based entity model(GTP-EM) is presented for underground real 3D integral representation and modeling.With object-oriented method,the topological relations are defined by geometrical elements.With the 3D integral geo-entity representation and modeling for the subway and its surrounding strata located underground,the central business district(CBD) in Beijing city is taken as an example.

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[149]
Wu Q, Xu H, Zou X, 2005. An effective method for 3D geological modeling with multi-source data integration.Computers & Geosciences, 31(1): 35-43.The existing 3D geological modeling systems rely heavily on large numbers of borehole and cross-section data. However, it is well known that the available geological data are generally sparse and undersampled. In this paper, we propose a stepwise refinement method for 3D modeling with multi-source data integration. The method can naturally simulate geological structures no matter whether the available geological data are sufficient or not. By stepwise refinement on multiple data, the method increases the accuracy of 3D models gradually and effectively. In addition, the mechanisms used in the method for organizing and manipulating information can have an equally important impact upon geologists thought, the interpretation of geological data, and 3D modeling methodology. A concrete example of using the method to Huai Bei fault and fold belt shows that the method can be applied to broad and complex geological areas.

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[150]
Wu X F, Wang Z G, Liu C Met al., 2002. Digital rainfall-runoff model based on DEM: The application to Xiaolangdi-Huayuankou Section of the Yellow River Basin.Acta Geographica Sinica, 57(6): 671-678. (in Chinese)DEM is the main data source which is used in watershed analysis. There are many mature algorithms in watershed analysis and they can be used to delineate the drainage networks. Applications of the methods based on DEM make significant innovation in hydrological simulations. Topographic parameters which are used in hydrological models can be automatically calculated from DEM. The article introduces the main process to determine watershed geometry, drainage network and other map-type information for hydrological models. Lushi basin, located in the upper Luohe river which is a tributary of the middle Yellow River, was selected as the study region with an area of 4,623 km2. WMS6.1, a GIS hydrological tool, which is introduced to China recently, was used to develop the digital rainfall-runoff model, and other GIS tools such as ARC/Info, Arcview were also used to deal with the data. The drainage network was derived from 1:250,000 DEM, and the region was divided into seven sub-basins. HEC-1 model, a part of hydrological models in WMS, was selected to simulate the rainfall-runoff process. Curve Numbers (CNs) and other parameters were automatically calculated to input to models directly. Five historical flood events were simulated. The results demonstrate that the method was more efficient than trade method. Although it is very easy and quick to input and output data for the models, it does not mean that the hydrological model itself has high quality, so it is necessary to develop hydrological models which can be adapted to the region.

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[151]
Xiao J X, Fang T, Zhao Pet al., 2009. Image-based street-side city modeling. ACM Transactions on Graphics, 28(5): 114.1-114.12.We propose an automatic approach to generate street-side 3D photo-realistic models from images captured along the streets at ground level. We first develop a multi-view semantic segmentation method that recognizes and segments each image at pixel level into semantically meaningful areas, each labeled with a specific object class, such as building, sky, ground, vegetation and car. A partition scheme is then introduced to separate buildings into independent blocks using the major line structures of the scene. Finally, for each block, we propose an inverse patch-based orthographic composition and structure analysis method for façade modeling that efficiently regularizes the noisy and missing reconstructed 3D data. Our system has the distinct advantage of producing visually compelling results by imposing strong priors of building regularity. We demonstrate the fully automatic system on a typical city example to validate our methodology.

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[152]
Xie S P, Du J K, Wang L C, 2005. Methods for processing depression and flat areas in extracting drainage net- works based on the DEM.Advances in Water Science, 16(4): 535-540. (in Chinese)How to process depression and flat areas and their drainage direction is a key issue and must be solved prior to the extraction of drainage network based on the digital elevation model(DEM).This paper investigates the shortcomings of the ex- isting methods for the complex terrain DEM with depressions and flat areas, and proposes several new methods, namely, the classification and the merger of depressions, the valid filling depression, the classification of flat areas, and the construction of the drainage direction based on the flow cost for the river valley plains.These methods can be performed in the software system developed by authors.The test shows that the methods mentioned above can be used to process complex depressions validly and construct flat areas water flow direction in the consideration of the ambient terrain and astringency to the potential waterway. And they are proved to be rational.In addition, by using the methods, odd waterways such as parallel and pseudo ones can be generated in the extraction of the drainage network.Hence the results obtained are consistent with the real situation.

[153]
Xie Y Q, Tang G A, Jiang L, 2013. Characteristics and correcting methods of errors in extraction of SOA based on DEMs.Geography and Geo-Information Science, 29(2): 49-53. (in Chinese)Slope of Aspect(SOA) is a key index in reflecting the horizontal variance ratio of terrain surface,and plays an important role in many fields of digital terrain analysis,such as slope spectrum,terrain features and visualization,etc.SOA can be extracted efficiently from DEM,and usually can be acquired by extracting SOA matrix derived from DEM.Guoan Tang noticed the influence of the periodicity of aspect in the extraction process,and proposed a method by a combination of original and reverse DEMs.This method avoids errors brought by the ignorance of this influence,thus is now generally accepted and used.But through further study,it still has serious deficiencies.It fails to consider the influence brought by slope extraction algorithm,of which the relationship of the six pairs of differences can bother the whole process,so a large number of errors are left in its extraction result.In this paper,the relationship of those differences is analyzed in details,and a new model is built.The new method is named as senary division method,and it avoids the mistakes by dividing slope extraction algorithm into six parts,and correcting errors in each part separately according to two major criteria established in this paper.The new algorithm is developed based on ArcEngine.Using 5 m resolution DEMs as source data,a comparison is made between the old and the new method.The comparison shows that about 12.77 percent of SOA extraction results obtained by the old method still need correction in regions where SOA is over 80,and about 1.9 percent of the whole extraction results have values at least one bigger than correct ones.Moreover,the errors in the results extracted by the old method distribute mainly at the lines of ridges and valleys,where the values of aspects varied intensely.These errors are corrected by the new method successfully,and this demonstrates the validity of the new method.

[154]
Xiong L Y, Tang G A, Josef Set al., 2016a. Paleotopographic controls on loess deposition in the Loess Plateau of China.Earth Surface Processes & Landforms, 41: 1155-1168.The underlying pre-existing paleotopography directly influences the loess deposition process and shapes the morphology of current loess landforms. An understanding of the controlling effects of the underlying paleotopography on loess deposition is critical to revealing the mechanism of loess-landform formation. However, these controlling effects exhibit spatial variation as well as uncertainty, depending on a study's data sources, methodologies and particular research scope. In this study, the geological history of a study area in the Loess Plateau of China that is subject to severe soil erosion is investigated using detailed geological information and digital elevation models (DEMs), and an underlying paleotopographic model of the area is constructed. Based on the models of modern terrain and paleotopography, we introduce a watershed hierarchy method to investigate the spatial variation of the loess-landform inheritance relationship and reveal the loess deposition process over different scales of drainage. The landform inheritance relationships were characterized using a terrain-relief change index (TRCI) and a bedrock terrain controllability index (BTCI). The results show that the TRCI appears to have an inverse relationship with increasing research scope, indicating that, compared with the paleotopography of the region, modern terrain has lower topographic relief over the entire area, while it has higher topographic relief in the smaller, local areas. The BTCI strengthens with increasing drainage area, which demonstrates a strong controlling effect over the entire study area, but a weak effect in the smaller, local areas because of the effect of paleotopography on modern terrain. The results provide for an understanding of the spatial variation of loess deposition in relation to paleotopography and contribute to the development of a process-based loess-landform evolution model. Copyright 2015 John Wiley & Sons, Ltd.

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[155]
Xiong L Y, Tang G A, Li F Yet al., 2014a. Modeling the evolution of loess-covered landforms in the Loess Plateau of China using a DEM of underground bedrock surface.Geomorphology, 209(1): 18-26.The evolution of loess-covered landforms is largely controlled by the pre-Quaternary underlying bedrock terrain, which is one of the most important factors in understanding the formation mechanism of the landforms. This study used multiple data sources to detect 1729 outcropping points of underlying terrain, in order to construct a digital elevation model (DEM) of the paleotopography of an area of the Loess Plateau subject to severe soil erosion. Four terrain characteristics, including terrain texture, slope gradient, the hypsometric curve, and slope aspect, were used to quantify topographic differences and reveal the loess-deposition process during the Quaternary. A loess thickness map was then created to show the spatial distribution of loess deposits in the test area. Finally, the geomorphological inheritance characteristics of the loess-covered landforms were evaluated in different landform divisions. The results showed the significant inheritance of modern topography from the underlying topography with a similar general relief trends. The average thickness of loess deposits was computed to be 104.6 m, with the thickest part located in the Xifeng loess tableland area. In addition, the slope aspects of the North and Northwest seem to have favored Quaternary loess deposition, which supported the hypothesis of an eolian origin for loess in China. The modern surface has lower topographic relief compared to the underlying terrain due to loess deposition.

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[156]
Xiong L Y, Tang G A, Yan S Jet al., 2014c. Landform-oriented flow-routing algorithm for the dual-structure loess terrain based on digital elevation models.Hydrological Processes, 28(4): 1756-1766.The loess landform in the Loess Plateau of China is with typical dual structure, namely, the upper smooth positive terrain and the lower cliffy negative terrain (P–N terrain for short). Obvious differences in their morphological feature, geomorphological mechanism, and hydrological process could be found in the both areas. Based on the differences, a flow-routing algorithm that separately addresses the dual-structure terrain would be necessary to encompass this spatial variation in their hydrological behaviour. This paper proposes a mixed flow-routing algorithm to address aforementioned problems. First, the loess landform surface is divided into P–N terrains based on digital elevation models. Then, specific catchment area is calculated with the new algorithm to simulate the water flows in both positive and negative terrain areas. The mixed algorithm consists of the multiple flow-routing algorithm (multiple-flow direction) for positive areas and the D8 algorithm for negative areas, respectively. The approach is validated in two typical geomorphologic areas with low hills and dense gullies in the northern Shaanxi Loess Plateau. Four indices are used to examine the results, which show that the new algorithm is more suitable for loess terrain in simulating the spatial distribution of water accumulation, as well as in modeling the flow characteristics of the true surface by considering the morphological structures of the terrain. Copyright 08 2013 John Wiley & Sons, Ltd.

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[157]
Xiong L Y, Tang G A, Yan S J, 2013. Grading extraction method of saddles based on DEM.Science of Surveying and Mapping, 38(2): 181-183. (in Chinese)Saddle is the steepest terrain feature point in the evaluation of landform units,which conveys the basic landform morphology and the hierarchical structure.In this paper,a method was designed to extract the saddle points of land reliefs by the notion that saddle points are relatively low points on the watershed boundaries,which were extracted by a carefully designed D8 procedure.The method was validated in a typical geomorphologic area with low hills and dense gullies in the northern Shaanxi Loess Plateau.Experimental result showed that the terrain saddle extracted by this method could inherit the characteristics of high precision,simple extraction,better conveying the hierarchical structure of landforms,and remain the spatial relationship with peaks so as to determine hierarchical levels of the saddles.It is a vital way of constructing the landform characteristic retained terrain feature point clusters.

[158]
Xiong L Y, Tang G A, Yuan B Yet al., 2014b. Geomorphological inheritance for loess landform evolution in a severe soil erosion region of Loess Plateau of China based on digital elevation models.Science China Earth Sciences, 57(8): 1944-1952.

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[159]
Xiong L Y, Tang G A, Zhu A Xet al., 2016b. Landform-derived placement of electrical resistivity prospecting for paleotopography reconstruction in the loess landforms of China.Journal of Applied Geophysics, 131: 1-13.The paleotopography of loess landform represents the initial surface before the evolution of the Aeolian depositional process. This paleotopography served as an indicator of the paleo-geography and erosion base that restrained the evolution of the current landform. In this case study, a landform-derived placement method involving electrical resistivity prospecting is proposed for paleotopography reconstruction. The method consists of extracting terrain feature knowledge and terrain feature-based paleotopography prospecting and reconstruction. The field experiment is validated and used in three typical loess landform areas in the Chinese Loess Plateau. These typical loess landforms include loess hill, loess ridge, and loess tableland. Terrain features considered include peaks, saddles, ridges, and gullies. The results show significant electrical resistivity difference between the paleotopography and loess strata. The electrical resistivity method could effectively detect the paleotopography and different loess layers. The reconstructed paleotopography using the feature-based method could effectively represent the morphology of the paleosurface compared to the result of the interpolation method. The reconstructed paleotopography also appears as a coincident terrain relief compared to modern topography; such a relief demonstrates significant landform inheritance between modern terrain and paleotopography. In the loess hill and ridge landform areas, the relative elevation difference of paleotopography is approximately 50 m whereas that of the modern terrain is roughly 150 m, indicating that the loess deposition process increased the topographic relief from paleotopography to modern terrain by approximately 100 m. Similar altitude of the paleotopographic peaks (roughly 10 m height difference) appears in the two nearby loess ridge and hill areas. The results indicate that paleo-geography of this area should be a landform of peneplain and almost a planation surface.

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[160]
Xiong L Y, Tang G A, Zhu A Xet al., 2017b. Paleotopographic controls on modern gully evolution in the loess landforms of China.Science China Earth Sciences, 60(3): 438-451.The inhomogeneous and non-flat paleotopography in a depositional landform area profoundly controls the process of modern gully evolution and shapes the structure of a gully network. However, this controlling effect of paleotopography on modern gully evolution is mostly ignored because of the difficulties in paleotopography reconstruction. In this study, loess area in China is selected as case area for its typical depositional landform area and inhomogeneous and non-flat paleotopography during the Quaternary. The paleotopography underlying loess is considered while evaluating its controlling effects on the gully evolutionary process. On the basis of the geophysical prospecting, detailed geological information, and high-resolution digital elevation model, we reconstruct the pre-Quaternary paleotopographic surface in the case area. Comparative analysis is conducted to reveal the modern gully evolution in relation to the paleotopography. Results show that the concave area of the paleotopography acts as the basement of the high-order modern gully evolution in the hilly-gully area, although this concave area can be covered and buried by the loess depositional process during the Quaternary. A significant controlling effect of paleotopography on high-order modern gully evolution can be observed in a depositional landform with a hilly-gully underlying topography, whereas a relatively weak controlling effect exists in a flat underlying topographical area because of the strong horizontal shift effect of gully formation process. Several low-order modern gullies also exist and limit the controlling effect of paleotopography. These results reveal a controlled high-order modern gully evolutionary process and a rather dynamic low-order modern gully evolutionary process in the hilly-gully area. These results also help us understand the variations in different modern gully evolution in relation to paleotopography and the different management schemes for soil conservation and ecological restoration during the gully evolutionary process.

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[161]
Xiong L Y, Tang G A, Zhu A X, 2017a. A peak-cluster assessment method for the identification of upland plana- tion surfaces.International Journal of Geographical Information Science, 31(2): 387-404.Abstract Residual upland planation surfaces serve as strong evidence of peneplains during long intervals of base-level stability in the peneplanation process. Multi-stage planation surfaces could aid the calculation of uplift rates and the reconstruction of upland plateau evolution. However, most planation surfaces have been damaged by crustal uplift, tectonic deformation, and surface erosion, thus increasing the difficulty in automatically identifying residual planation surfaces. This study proposes a peak-cluster assessment method for the automatic identification of potential upland planation surfaces. It consists of two steps: peak extraction and peak-cluster characterization. Three critical parameters, namely, landform planation index (LPI), peak elevation standard deviation, and peak density, are employed to assess peak clusters. The proposed method is applied and validated in five case areas in the Tibetan Plateau using a Shuttle Radar Topography Mission digital elevation model (SRTM DEM) with 3 arc-second resolution. Results show that the proposed method can effectively extract potential planation surfaces, which are found to be stable with different resolutions of DEM data. A significant planation characteristic can be obtained in the relatively flat areas of the Gangdise yainqentanglha Mountains and Qaidam Basin. Several vestiges of potential former planation areas are also extracted in the hilly-gully areas of the western part of the Himalaya Mountains, the northern part of the Tangula engduan Mountains, and the northeastern part of the Kunlun inling Mountains despite the absence of significant topographical features characterized by low slope angles or low terrain reliefs. Vestiges of planation surfaces are also identified in these hilly-gully upland areas. Hence, the proposed method can be effectively used to extract potential upland planation surfaces not only in flat areas but also in hilly-gully areas.

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[162]
Xu A L, Wang P, 2010. SWAT-based simulation of pollution from non-point agricultural sources.Environmental Monitoring & Forewarning, 2(1): 38-43. (in Chinese)The SWAT model was applied to polder areas to simulate the behaviors of non-point agricultural sources in the Lake Taihu Watershed.For this purpose,a non-point source pollution information database was established and the data extracted from the parameter process was integrated into the database.A table was set up within the database to build linkage between data fields and parameters,resolving the problem of automatic assignment of numerous discrete elements.The drawbacks of SWAT model used in the polder areas were overcome with the dummy reservoir technology.

[163]
Xu J W, Zhang W C, Fu C B, 2007. A new method for treating the depressions and flat areas in DEM for large-scale hydrology and climate models.Journal of Hydraulic Engineering, 38(12): 1414-1420. (in Chinese)The new method is composed of two algorithms for processing the depressions and plain areas in DEM.The first one is quantile classification algorithm which utilizes the statistics characteristics to compute the quantile and carries out the classification.Since its time complexity is O(N),the working speed is much faster than the traditional method.The other algorithm further processes the quantilized depressions and flat areas initiated from the lowest elevation until the end.The assessments by using various method based on DEM with 90脳90 grids show that the new method has very high processing speed.In average,this method is faster than the Jenson Domingue method by thousands times.

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[164]
Xue J, Chen W, Cao Y, 2013. The definition of urban concentrated areas and the relations with the national main function areas of China.Scientia Geographica Sinica, 33(6): 649-658. (in Chinese)The urban concentrated area is a form of regional organization in the advanced stage of urbanization.It is benefit for clearing national development framework and promoting regional integration to divide and identify the urban concentrated area spatially.Based on the existing research results,according to the level and stage of China's urbanization,this article defines the space identification standards of urban concentrated areas in China,including such aspects as the core city,standard city,other small cities and towns,and boundary identification,then divide Chinese cities into 15 typical urban concentrated areas and 8 quasi-urban concentrated areas based on the traffic accessibility.They present a spatial pattern of "three vertical and two horizontal distributions",which construct a national system of urban concentrated areas.Compared with the main function areas of the national plans,the proposed program of urban concentrated areas is consistent with the strategy pattern of urbanization in the national plans of main function areas on the whole.Under the guidance of the strategy of the national main function areas,the urban concentrated areas should develop in the light of the positions and goals in the plans to select the right path and direction.

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[165]
Xue X W, Chen X, Zhang Z Cet al., 2009. Categorization of karst landform on the basis of landform factor ei- genvalue.Carsologica Sinica, 28(2): 175-180. (in Chinese)In this paper,digital elevation model(DEM)is used to divide sub-basin and seven landform factors that affect the karst geomorphology,including elevation,slope,relief amplitude,surface roughness,surface incision and elevation variance coefficient as well as topographic index,are extracted.A method of terrain factor eigenvalue is proposed for categorizing karst landform.Houzhai basin was chosen to be divided into eighteen basins.Sixteen basins were selected to distinguish their landform type,and the other two are chosen for the method verification.The statistical analysis of a single landform factor and fuzzy cluster analysis of multi-landform factors of the landform factor eigenvalue are carried out in order to determine the threshold of the peak cluster and peak forest landform in the Houzhai basin.The results demonstrate that the method based on landform factor eigenvalue is suitable for quantitative categorization of karst basin landform.

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[166]
Yan D C, Bai J J, Zhang R L, 2009. Voronoi-based distribution measure of point objects in adjacent space.Geo- matics and Information Science of Wuhan University, 34(1): 44-47. (in Chinese)The measure of adjacent space's distribution researches into objects' distribution in adjacent space.It is the important basis of geographic analysis,environmental assessment,also location optimization.A Voronoi-diagram based method to measure adjacent spatial distribution is proposed,which dynamically determines the related extent according to measure point's Voronoi adjacent relation,and assesses the adjacent space's distribution based on the index of adjacent distribution.The method can measure any point's adjacent distribution.Furthermore,it can be used to evaluate the dispersion degree at overall level.Finally,an applied example evaluating the development of building lots and landscape protection is given to illustrate the application prospects.

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[167]
Yan S J, Tang G A, Li F Yet al., 2011. An edge detection based method for extraction of loess shoulder-line from grid DEM.Geomatics and Information Science of Wuhan University, 36(3): 363-367. (in Chinese)We propose a new method for extracting loess shoulder-lines from grid DEM.The morphological characteristics of loess shoulder-lines are investigated firstly.By applying the edge detection approach,a new method for extracting loess shoulder-line candidate points is proposed based on the prominent height variation of the points.The algorithm then connects the candidate points to small line segments by morphological methods.Finally,precise,systematic loess shoulder-lines are extracted after refining the line segments.Experiments in the loess hill area show that the extracted lines from gradient based operators,such as Sobel,Roberts and Prewitt,have relatively poor results on both integration and matching precision with manually extracted loess shoulder-lines,while loess shoulder-lines extracted by LOG operator has very good matching ratio to the manually extracted loess shoulder-lines.So LOG is an ideal loess shoulder-lines extraction operator and can be used to extract loess shoulder-lines effectively and automatically.

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[168]
Yang L, Zhu A X, Qin C Zet al., 2011. A soil sampling method based on representativeness grade of sampling points.Acta Pedologica Sinica, 48(5): 938-946. (in Chinese)Sampling design plays a critical role in capturing information about spatial distribution of soils,influences directly the accuracy of samples-based soil mapping.The commonly used methods are often confronted with such problems as the need for large amounts of samples and low sampling efficiency.When the resources available are inadequate for accomplishing a large volume of sampling once for all,additional sampling has to be done many times and in batches.However,the present in-batches sampling methods mostly take into account supplementality of the batches of sampling points in geographic space,which lead to overlapping of the sampling points in attribute space,affecting efficient utilization of the resources.In view of this,clustering analysis of soil environmental co-variates was performed to explore for sampling points representative of different grades of soil spatial distribution and to formulate a sampling designing method based on representativeness grade.This proposed method was applied to the study area located in Heshan Farm,Nenjiang County,Heilongjiang Province,and digital soil mapping was done using selected sampling points of different representativeness grades for verification of the methods.Results show that only a small number of sampling points of the highest grade could obtain most of the main soil types(sub-order in Chinese Soil Taxonomy) and soil mapping was high in accuracy;and addition of sampling points lower in representative grade could raise the accuracy of soil mapping;but the accuracy did not improve much when the number of sampling points added exceeded a certain level.Therefore,compared with the number of sampling points,representativeness grade of the points was more important to accuracy of soil mapping.The representativeness grade system proposed in this paper can be used as reference for sequencing of sampling points and is contributive to formulation of high-efficiency stepwise sampling design.

[169]
Yang Q K, Li R, Cao M Met al., 2006. Advances of quantitative assessment on regional soil erosion.Advances in Earth Science, 21(8): 849-856. (in Chinese)Because of the increasing demands for soil and water conservation policy-making,progress in soil erosion science and increasing global change in recent years,research into the quantitative assessment and modeling of regional soil erosion has taken on great importance.Recent research outcomes include soil erosion surveys at global,regional and national scales;establishing processes and scale effects in regional soil erosion,extraction of factors underlying regional soil erosion and the development of regional soil erosion models.The trend in quantitative regional soil erosion research is to treat regional soil erosion as a component of general land surface processes and take into account the effects of global change on regional erosion.Successful outcomes have used integrated remote sensing and GIS technologies with distributed regional soil erosion models to produce quantitative evaluations of soil erosion characteristics at multiple scales.This paper discusses the state of current quantitative assessment of regional soil erosion and suggests that further intensive study is needed in(1) quantitative analysis of regional soil erosion processes using spatio-temporal scaling approaches,(2) development of distributed regional soil erosion models,(3) dynamic analysis and prediction of regional erosion,(4) the relationships between soil erosion and the effects of global change,and(5) establishment of information infrastructure for data processing and management.

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[170]
Yang Q K, Shi W J, Tim Ret al., 2007. On constructing methods of hydrologically correct DEMs.Science of Soil and Water Conservation, 5(4): 1-6. (in Chinese)Hydrologically correct DEMs(Hc-DEM) is one of DEMs which correctly and sufficiently represents genesis and locational relationship between hydrologic parameters,including direction and pathway of overland runoff,stream networks,and boundary of watershed,and landform,etc.As the only way to extract terrain parameters based on DEMs for the studies of watershed hydrology,and soil erosion modeling of regional scale,therefore it is necessary to constructing Hc-DEMs for representing terrain shape,extracting terrain and hydrology parameters.In this paper,the concept,constructing method of Hc-DEMs were introduced and discussed,then taking Loess Plateau as an example,key parameters for Hc-DEMs constructing based on digital topographic maps and ANUDEM software package were identified by series tests;the quality of resultant DEMs have been assessed by comparing them to DEMs from TIN approach which is widely applied in China.The results show that varied resolution Hc-DEMs can be generated based on available digital topographic maps,including features of contour,spot heights,stream lines,etc,and ANUDEM software,and provide solid support for hydrology and soil erosion modeling at the watershed/regional scales,and mapping of vegetation suitability.

[171]
Yang Q K, Zhao M D, Liu Y Met al., 2009. Application of DEMs in regional soil erosion modeling.Geomatics World, 7(1): 25-32. (in Chinese)Terrain is a primary factor to affect the hydrological and erosion processes.Slope gradient and length,etc,are key parameters of soil erosion prediction models and watershed hydrological models.Researches on the application of DEMs and digital terrain analysis in re-gional soil erosion modeling include:how to make a representation of terrain shape and gullies structures and enhance to generate hydrologically correct DEM;which parameters or variables to be used to describe the influences of terrain on soil erosion processes at the multiple scales;how to extract the ero-terrain factors based on digital terrain analysis,GIS spatial analysis,and digital image processing strategies;and how to make a algorithms for relationship between ter-rain variables and soil erosion.By introducing advanced views of terrain representation and in-terpolation algorithm from western and improving the DEMs based on higher accuracy hypsog-raphy data and digital topography maps,taking scaling issues into account and integrating the existed researches on erosion terrain factors and regional soil erosion model,are key issues in this study field in the future.

[172]
Yang X, Tang G A, Liu X Jet al., 2009. Digital terrain analysis: Theory, method and application.Acta Geographica Sinica, 64(9): 1058-1070. (in Chinese)Through 50 years of development,theory and methodology of DEM itself and DEM based digital terrain analysis (DTA) have been matured gradually,and played key roles in hydrology,geomorphometry,soil sciences,environmental science,agriculture,geologic hazard,civil engineering and military affairs. Based on an overall retrieval analysis of previous researches,this paper classifies different methods of DTA into four classes,i.e. analysis of terrain factor,terrain feature extraction,terrain statistical analysis and DEM based geo-modeling. Secondly,uncertainty and the scale issue of DTA are discussed. Besides,this paper points out that scale effect,optimal scale and scale transform are three basic scale issues of DTA. Thirdly,applications of DTA in geomorphometry,hydrology,soil science,agriculture,geologic hazard are introduced. Finally,this paper proposes that the conceptual framework of DTA,the accuracy of DEM modeling and the method of terrain analysis need to be improved,especially the integrated method of DEM embedded geographical modeling,for the simulation of more lifelike natural environment.

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[173]
Yang X, Tang G A, Wang L, 2004. Modeling of radiation over rugged areas based on DEM.Geography and Geo-Information Science, 20(5): 41-44. (in Chinese)Through extracting a series of related topographic parameters,such as slope gradient,aspect,and terrain shading areas,the digital model of direct radiation and diffuse radiation and global radiation is conducted by the means of a GIS based on overlay processing.The experiment shows that the regional distribution of solar radiation could be effectively visualized and quantified.It could be of critical significance for the research of regional microclimate,agricultural programming and the application of solar energy.

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[174]
Yang X, Tang G A, Xiao C Cet al., 2007. Terrain revised model for air temperature in mountainous area based on DEMs.Journal of Geographical Sciences, 17(4): 399-408. (in Chinese)

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[175]
Yao Y H, Zhou C H, Sun R Het al., 2007. Digital mapping of mountain landforms based on multiple source data.Journal of Mountain Science, 25(1): 122-128. (in Chinese)With the further combination of “3S” with geosciences, it has great influence on mapping methods of traditional geomorphologic cartography. Firstly, remote sensing data is not only an important assistant measure for ground survey, but also an important data source which can be zoom in or zoom out to certain scales according to needs, which changes the data sources of traditional geomorphological cartography. Secondly, data with different sources such as relief map (DEM), vegetation map, geological map and remote sensing data can be integrated, overlapped and calculated in GIS environment, and this totally changes the mapping methods of traditional geomorphological cartography which was depended on generalization from topographical map by several times and makes it possible for quantitative interpretation of geomorphological information based on multiple-data-sources. In order to establish a set of methods for geomorphological interpretation on scale 1∶1,000,000, this paper discussed the ways and the functions of different data for landform interpretation and the interpretation methods of geomorphological information based on multiple-data-sources. Changdu Sheet in Tibet Plateau was our experiment area.

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[176]
Ye R H, Song Z Y, Shen Zet al., 2013. A visualization system for numerical simulation of storm surges in Pearl River Estuary. Journal of Hohai University (Natural Sciences), 41(3): 260-264. (in Chinese)A visualization system was designed and established for numerical simulation of storm surges in the Pearl River Estuary.This system was achieved through hybrid programming,which combines the advantages of Fortran and geographic information systems(GIS) in terms of numerical calculation and visualization,respectively.The system encapsulates and integrates the numerical model for simulating storm surges based on the ELCIRC model,and provides a GUI interface,which is convenient for setting model parameters and boundary conditions.The system also includes functions such as dynamically displaying typhoon paths,drawing hydrographs of tides,visualizing current fields,and thereby making it easy for users to post-process and analyze calculation results.Application results show that the system is user-friendly and stable,and has high simulation precision.

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[177]
Yi H W, Tang G A, Liu Y Met al., 2003. Stream runoff nodes and their derivation based on DEM.Journal of Soil and Water Conservation, 17(3): 108-111. (in Chinese)This paper put forward the concept of "stream runoff node" firstly, which could be regarded as a critical development in recognizing and analyzing the hydrological and geographical characteristic of stream networks. The major characteristics of runoff nodes were investigated. Including how runoff nodes could effectively reflect drainages terrain and relief features, their dynamic variation and spatial distribution etc. Finally, a GIS based method of deriving runoff nodes from DEM were preliminarily discussed.

[178]
Yu G, Lai G Y, 2007. Simulation assessment on nutrient transport in Taihu Lake Basin. Journal of Hehai Univer- sity (Natural Sciences), 351(2): 140-144. (in Chinese)Based on the observed meteorological,hydrological,and water quality data and social and economic statistical data of 1995,1998,and 2002,and with the SWAT model as the simulation tool,a simulative analysis of 5 nutrient sources,including soil nutrient background,urban and rural domestic sewage discharge,industrial point source discharge,livestock breeding discharge,and the use of fertilizers,was performed for the intake area on the upper Taihu Lake Basin. The simulated result shows that the domestic sewage and industrial point sources are the main nutrient sources,and that the non-point source nutrients,such as fertilizers,livestock breeding,domestic sewage,soil nutrient background,are the main forms of external nutrient sources discharged into the Taihu Lake.Of the total amount of nutrient salt discharged into the lake,about 86% of TN and 88% of TP are closely related to the human activities.T he contribution ratios of TN and TP discharged into the lake are of obvious spatial difference.Moreover,Huxi district and Wuyu district are the leading sections of external nutrients discharged into the Taihu Lake.

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[179]
Yu Z Y, Yuan L W, Xie Z R, 2008. Fluctuation process and trend prediction of sea level change along Jiangsu coast based on multi-scale analysis.Scientia Geographica Sinica, 28(1): 94-99. (in Chinese)In this paper three tide gauge stations along the coast of northern part of Jiangsu Province were selected as the objects of study,which were located in the sustainable slowly settlement areas of Changjiang(Yangtze) River Delta.Fluctuation and trend of sea level change were analyzed in virtue of EMD and SSA methods comprehensively.The adjusted long-term trends were obtained through the sum of trends that extracted by EMD and long-term cycle components.Short-term wave cycles were gained from the rest components by means of SSA method and each station could be properly compared.Combined with the research findings of local ground rise or fall,the absolute sea level changes were discussed and prediction models were built according to the adjusted long-term trends.Based on the mentioned above,relative sea level changes in the coming one hundred years were calculated and compared with results of IPCC.

[180]
Yuan L W, Yu Z Y, Xie Z Ret al., 2009. ENSO signals and their spatial-temporal variation characteristics re- corded by the sea-level changes in the northwest Pacific margin during 1965-2005.Sci China Ser D-Earth Sci, 52(6): 869-882. (in Chinese)

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[181]
Yuan Y F, Zhu P M, Zhao Net al., 2013. Automatic identification of circular mare craters based on mathematical morphology. Scientia Sinica (Physica, Mechanica & Astronomica), 43(3): 324-332.Identification of lunar crater is very significant, because the crater is not only the most common geological unit on the surface of the moon, but also an important object to study lunar geological evolution history and the fundamental basis of lunar geological dating. This paper conducts to recognize and extract the craters automatically based on mathematical morphology, from the lunar CCD image acquired by the Chang'e I satellite. The grayscale of the crater rims vary obviously in the CCD image, and their gradient are large, which can be calculated to obtain the shape of crater rim. In general, results of crater rims extracted by edge detection based on sharp grayscale gradient of image are discontinuous and rough, and also have gaps and holes. Some processings are further done to take the smooth and continuous arcs of crater rims, by measuring and extracting the corresponding shape from the image with a certain form of structural elements according to the basic idea of mathematical morphology. And then processed arcs may be used to fit the rims of craters conveniently and to obtain the diameters and locations of craters. The algorithm based on mathematical morphology for crater identification is as follows: firstly, we calculate the gradient of grayscale of the CCD image to form a gradient image, and binarize it; then separate the rims by mathematical morphology; finally extract the sizes and locations of craters by fitting rims with circles. In this paper, experiments on identification of craters in lunar mare and terra area show that the algorithm designed by authors may identify the crater with smallest diameter of 10 pixels. The identification of mare craters is accurate and reliable, while of terra craters is a little worse, due to big grayscale variety in CCD image background caused by big lithological differences and fluctuant topography, so we need a futher study on improvement of algorithm.

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[182]
Yue T X, 2011. Progress in earth surface modeling.Journal of Remote Sensing, 15(6): 1105-1124. (in Chinese)A definition of earth surface modeling is proposed on the basis of discussing the concept of earth surface.Studies on earth's surface topography modeling and climate system modeling are reviewed,which indicates that it is eagerly necessary to develop simulation methods with high speed,high accuracy and low memory requirement.Introduction of methods for high accuracy and high speed surface modeling(HASM),developed by means of the fundamental theorem of surfaces,might be an efficient way to characterize the states of earth-surface and changes in those states.

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[183]
Yue T X, Du Z P, Song D Jet al., 2007. A new method of surface modeling and its application to DEM construc- tion.Geomorphology, 91(1/2): 161-172.A new method of surface modelling based on the fundamental theorem of surfaces (SMTS) is presented. Eight different test surfaces are employed to comparatively analyze the simulation errors of SMTS and the classical methods of surface modeling in GIS, including TLI (triangulated irregular network with linear interpolation), SPLINE, IDW (inverse distance weighted) and KRIGING. Numerical tests show that SMTS is much more accurate than the classical methods. SMTS theoretically gives a solution to the error problem that has long troubled DEM construction. As a real-world example, SMTS is used to construct a DEM of the Da-Fo-Si coal mine in Shaan-Xi Province, China. Its root mean square error (RMSE) is compared with those of DEMs constructed by the four classical methods. The results show that although SMTS also has a higher accuracy in the real-world example, the improvement of accuracy is less distinct than that expected from the numerical tests. The accuracy loss seems to be caused by location differences between sampling points and the central points of lattices of the simulated surfaces. Two alternative ways are proposed to solve this problem.

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[184]
Yue Z Y, Di K C, Zhang P, 2012. Theories and methods for numerical simulation of impact crater formation.Earth Science Frontiers, 19(6): 110-117. (in Chinese)Numerical simulation is one of the main methods in impact crater formation study and an important means to understand its mechanism especially for large craters.The basic principle of numerical simulation of impact crater formation is to describe the material's motion and state under high velocity impact through computer code.The material and space are first divided into discrete meshes,whose deformation,motion and state will be calculated in each time step.Newton's Law of Motion,material constitutive model,and the equation of state are the theoretical basis in the numerical simulation of the crater formation.Newton's Law of Motion is implemented in the discrete meshes through partial differential equations,while the material constitutive model relates the yield strength to the damage,temperature,porosity,and vibration,and the equation of state is used to calculate the pressure within the meshes and the material state through other thermodynamic parameters.

[185]
Yue Z Y, Liu J Z, Wu G G, 2008. Automatic identification of circular mare craters based on object oriented classi- fication method.Chinese Science Bulletin, 22: 2809-2813.

[186]
Zhang C X, Chen M, Li R Ret al., 2015. A virtual geographic environment system for multiscale air quality analysis and decision making: A case study of SO2 concentration simulation.Applied Geography, 63: 326-336.The spatial decision support system (SDSS) is widely used in environmental problem management. In this paper, focusing on the air quality problem in the Pearl River Delta, China, we present a virtual geographic environment (VGE) system to integrate multiscale meteorological and air quality models for policy making. It is a comprehensive modeling tool to aid decision makers and various stakeholders to participate in air quality management by providing geographic visualizations and friendly interfaces. With nested multiscale models, a synthetic understanding of cross-boundary air quality processes can be captured to understand both regional and local effects. With the help of Linux-Apache-MySQL-Perl (LAMP) architecture, users can manage and retrieve modeling data and model parameterizations to reach a consensus on the simulation results and share modeling knowledge. Aided by a high-resolved emission inventory, such a multiscale system enables practical applications for various scenarios. As a case study, the system was applied to simulate and analyze the SO 2 concentration process and local contribution in the Hong Kong Special Administrative Region (HKSAR) based on hourly simulation results with spatial resolutions of 0.5 and 3km from multiscale models. The results from the multiscale modeling and the limited local contribution suggest that Hong Kong and the surrounding region should closely cooperate to develop a better environment.

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[187]
Zhang C X, Lin H, Chen Met al., 2014a. Scale matching of multiscale digital elevation model (DEM) data and the Weather Research and Forecasting (WRF) model: A case study of meteorological simulation in Hong Kong.Arabian Journal of Geosciences, 7(6): 2215-2223.It is becoming easier to combine geographical data and dynamic models to provide information for problem solving and geographical cognition. However, the scale dependencies of the data, model, and process can confuse the results. This study extends traditional scale research in static geographical patterns to dynamic processes and focuses on the combined scale effect of multiscale geographical data and dynamic models. The capacity for topographical expression under the combined scale effect was investigated by taking multiscale topographical data and meteorological processes in Hong Kong as a case study. A meteorological simulation of the combined scale effect was evaluated against data from Hong Kong Observatory stations. The experiments showed that (1) a digital elevation model (DEM) using 3 arc sec data with a 1 km resolution Weather Research and Forecasting (WRF) model gives better topographical expression and meteorological reproduction in Hong Kong; (2) a fine-scale model is sensitive to the resolution of the DEM data, whereas a coarse-scale model is less sensitive to it; (3) better topographical expression alone does not improve weather process simulation; and (4) uncertainty arising from a scale mismatch between the DEM data and the dynamic model may account for 38 % of the variance in certain meteorological variables (e.g., temperature). This case study gives a clear explanation of the significance and implementation of scale matching for multiscale geographical data and dynamic models.

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[188]
Zhang C X, Lin H, Chen Met al., 2014b. Scale compatibility analysis in geographic process research: A case study of a meteorological simulation in Hong Kong.Applied Geography, 52: 135-143.Scale is a fundamental concept in geography. Although multiscale data, models and other products are considered when studying geography, scale mismatching can produce adverse results. Thus, scale compatibility is becoming crucial for decoding dynamic and interactive geographic processes. This paper presents a definition of scale compatibility for studying geographic processes and partitions this concept into four levels: multiple processes, dimensional, type and component. These four levels operate differently, as described in detail to support the implementation of scale compatibility. Applying the procedure to assess scale compatibility, a meteorological simulation case study in Hong Kong was investigated with regard to the use of multiscale digital elevation model (DEM) data and the Weather Research and Forecasting (WRF) model. This case study considered spatial dimension, measurement scale type and component level. The experiments showed that using DEM data and a model with different resolution and grid spacing, respectively, affected the dynamic simulation capacity, even accounting for 38% of the mean absolute error (MAE) for temperature. Furthermore, our 3 and 30 arc sec resolution DEM data are relatively more compatible with the WRF model of 1km grid spacing. This case study not only helps to improve meteorological simulations by considering scale compatibility as an issue but also explains the significance and implementation of scale compatibility in geographic processes research.

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[189]
Zhang C X, Yang Q K, Li R, 2005. Advancement in topographic wetness index and its application.Progress in Geography, 24(6): 116-123. (in Chinese)Topographic wetness index, which takes into account the integrated effects of topography and soil hydraulic characters on soil moisture, plays important theoretical and applied potentials in the studies of spatial distribution of soil moisture. Considering the spatial-temporal variation in upslope contributing area, topographic wetness indexes were divided into three types, e.g. static, quasi-dynamic and full dynamic. The effects of computing methods of topographic wetness index and resolution of DEMs as well as the universality of the index should be analyzed discreetly in application of topographic wetness index. At the same time, for the apparent differences between the current assumptions of topographic wetness index and actual water cycling process and runoff mechanism in arid/semi-arid region, the research approaches and the conceive of the application of topographic wetness index are proposed for the Losses Plateau to provide theoretical and practical foundation for the vegetation restoration and the conservation of soil and water in the region.

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[190]
Zhang F, Huang X F, Li D R, 2009. Spherical projection based triangulation for one station terrestrial laser scan- ning point cloud.Acta Geodaetica et Cartographica Sinica, 38(1): 48-54. (in Chinese)A Triangulated Irregular Network(TIN)generating algorithm is proposed for one station terrestrial laser scanning point cloud.The algorithm is incremental insertion generating algorithm using spherical projection strategy.Previous 3D TIN generating algorithms have problem to get correct neighboring relation between points,so,spherical projection strategy is employed to resolve the problem.The strategy is on the basis of the characteristic of one station terrestrial laser scanning point cloud.Incremental insertion generating algorithm takes less computer space resource,so the algorithm is suit for the data set with large amount of points.Some details of generating spherical Delaunay TIN are described,they include:the data structure of the algorithm;the definition of the projective sphere;generating of initial TIN;the method to judge positional relationship between geometric objects;the method of directed searching for triangle and the spherical local optimization procedure.The processes are optimized to improve the algorithm's efficiency.There are two experiments comparing the proposed algorithm with Geomagic Studio to test the performance of the algorithm.The first experiment reveals that the proposed algorithm is more efficient than the Geomagic Studio,and the second experiment shows that the proposed algorithm could get the better results to generate TIN.

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[191]
Zhang F, Tang G A, Cao Met al., 2013. Simulation of positive and negative terrain evolution in small loess wa- tershed based on ANN-CA Model.Geography and Geo-Information Science, 29(1): 28-31. (in Chinese)

[192]
Zhang H M, Yang Q K, Li Ret al., 2012. Research on the estimation of slope length in distributed watershed erosion. Journal of Hydraulic Engineering, 43(4): 437-443. (in Chinese)Slope length is a factor which is hard to be extracted when USLE/RUSLE is applied to the watershed scale. This paper analyzes theoretically and proposes the distributed watershed erosion slope length to reflect the real value of slope length in topographic factor and using the accumulative slope length algorithm to extract Distributed Watershed Erosion Slope Length from DEM data considering the position of erosion, sedimentation, and channel networks. This method is applied to the Xiannangou catchment. The result shows that it is effective in expressing the relationship between slope length and the terrain with accurate outcomes and reasonable special distribution. This method is suitable for extracting and analyzing terrain factors based on DEM in watershed or regional scale.

[193]
Zhang H M, Yang Q K, Li Ret al., 2013. Extension of a GIS procedure for calculating the RUSLE equation LS factor. Computers & Geosciences, 52(1): 177-188.The Universal Soil Loss Equation (USLE) and revised USLE (RUSLE) are often used to estimate soil erosion at regional landscape scales, however a major limitation is the difficulty in extracting the LS factor. The geographic information system-based (GIS-based) methods which have been developed for estimating the LS factor for USLE and RUSLE also have limitations. The unit contributing area-based estimation method (UCA) converts slope length to unit contributing area for considering two-dimensional topography, however is not able to predict the different zones of soil erosion and deposition. The flowpath and cumulative cell length-based method (FCL) overcomes this disadvantage but does not consider channel networks and flow convergence in two-dimensional topography. The purpose of this research was to overcome these limitations and extend the FCL method through inclusion of channel networks and convergence flow. We developed LS-TOOL in Microsoft's.NET environment using C with a user-friendly interface. Comparing the LS factor calculated with the three methodologies (UCA, FCL and LS-TOOL), LS-TOOL delivers encouraging results. In particular, LS-TOOL uses breaks in slope identified from the DEM to locate soil erosion and deposition zones, channel networks and convergence flow areas. Comparing slope length and LS factor values generated using LS-TOOL with manual methods, LS-TOOL corresponds more closely with the reality of the Xiannangou catchment than results using UCA or FCL. The LS-TOOL algorithm can automatically calculate slope length, slope steepness, L factor, S factor, and LS factors, providing the results as ASCII files which can be easily used in some GIS software. This study is an important step forward in conducting more accurate large area erosion evaluation.

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[194]
Zhang H P, Yang N, Zhang Y Qet al., 2006. Geomorphology of the Minjiang drainage system (Sichuan, China) and its structural implications.Quaternary Sciences, 26(1): 126-135.Compared with the remarkably flat feature of the main body of the Tibetan Plateau,geomorphology of the peripheral areas varies greatly.As an example,the eastern margin of Tibetan Plateau is more diffuse and irregular than the northern and southern ones.The Minshan Mountain along with its adjacent regions form a series of escarpments,become one of the key continental escarpments.The Minjiang drainage basin is part of this series and is adjacent to the Sichuan Basin.Knowledges of the geomorphic features of the Minjiang drainage networks and drainage sub-basins,of the stream morphology and the morphometric relation between the slope and elevation of the Minjiang drainage basin are still lacking.The recently developed digital elevation model(DEM) makes it possible to rapidly quantify the topographic characteristics of areas ranging from local drainage basins to entire continents.A DEM-based topographic analysis of mountain belts have been recently carried out along cross-sections perpendicular to the main structures of different orogens,which has shown that the Minjiang drainage basin has distinct geomorphic characteristics.Results from SRTM-DEM-determined Minjiang drainage sub-basins and channel profiles have shown that the eastern and western tributaries of the Minjiang River are obviously asymmetric.Almost all the analyzed characters(such as the areas,perimeters and total channel lengths) of the eastern sub-basins(except 32~(#),46~(#) and 58~(#)) are smaller that those of the western ones.Areas and perimeters of most the western sub-basins are more than 100km~(2) and 100km respectively and the area of 15~(#)sub-basin even reaches up to 7202km~(2) or so.The total channel lengths within many western sub-basins are above 200km.Besides the above features,the eastern streams show a little lower bifurcation ratios within 3.0~4.0;however,these parameters of the western ones are almost between 4.1~5.0.Longitudinal channel profiles of western and eastern 5~(th) order streams indicate that the lengths of the longest channels within almost all the eastern sub-basins are less than 20km,but those of western ones are normally more than 20km.The relative higher drops and gradients presented by eastern longest streams show the existence of the higher incision rate along this region.Taking it into account that the same outcropping and climate conditions control the whole Minjiang drainage basin,it can be concluded that lower perimeter and area of drainage sub-basins,total channel length,bifurcation ratio and higher channel gradient within eastern sub-basins along the Minjiang mainstream maybe result from the differential uplift of the Minshan Mountain region within Late Cenozoic.The shorter streams and lower bifurcation ratios maybe indicate the undergrowth and newborn features of these eastern streams,which are also representative for the eastern uplift of the Minshan Mountain.

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[195]
Zhang H P, Zhang P Z, Fan Q C, 2011. Initiation and recession of the fluvial knickpoints: A case study from the Yalu River-Wangtian’e volcanic region, northeastern China.Science China Earth Sciences, 54(11): 1746-1753. (in Chinese)Initiation and recession of the knickpoints are significant boundary condition for processes of fluvial system.The distribution and recession rates of knickpoints contain information that provides a fundamental understanding of geomorphic processes.In the Yalu River-Wangtian'e volcanic region of northeastern China,broadly distributed flat lava terrain provides an ideal site to study the recession of fluvial knickpoints because knickpoints and waterfalls are well preserved here.Here we describe the distribution of knickpoints in the Yalu River-Wangtian'e volcanic region by combining DEM analysis and numerical modeling.Furthermore,we present a knickpoint celerity model,derived from stream-power incision model,to relate knickpoint recession rate to drainage area.We calibrate important empirical coefficients with our knickpoint celerity model;the best fit erosion coefficient (K) is 1.32 10 8,and the best fit drainage area exponent (m) is 0.69.Error analysis indicates a close correspondence between synthetic and real knickpoints.Finally,we show that knickpoint recession rates in the Yalu River-Wangtian'e volcanic region are 1-10 mm/a during the early stages of transient incision,and that the present rates are 1-6 mm/a.Our recession rate results are in good agreement with previous findings from the Aso Volcano and volcanoes near Boso Peninsula (Japan),which have a similar geologic history to the Yalu River-Wangtian'e volcanic region.Our present effort provides new insight into landscape evolution in the Yalu River-Wangtian'e volcanic region in northeastern China.

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[196]
Zhang Z X, Zhang J Q, Zhang L, 2000. VirtuoZo digital photogrammetry system [D]. Wuhan: Wuhan Technical University, 1-98. (in Chinese)

[197]
Zhang K, Sheng Y H, Lv H Y, 2015. Stereo matching cost computation based on nonsubsampled contourlet trans- form. Journal of Visual Communication and Image Representation, 26(C): 275-283.A new matching cost computation method based on nonsubsampled contourlet transform (NSCT) for stereo image matching is proposed in this paper. Firstly, stereo image is decomposed into high frequency sub-band images at different scales and along different directions by NSCT. Secondly, by utilizing coefficients in high frequency domain and grayscales in RGB color space, the computation model of weighted matching cost between two pixels is designed based on the gestalt laws. Lastly, two types of experiments are carried out with standard stereopairs in the Middlebury benchmark. One of the experiments is to confirm optimum values of NSCT scale and direction parameters, and the other is to compare proposed matching cost with nine known matching costs. Experimental results show that the optimum values of scale and direction parameters are respectively 2 and 3, and the matching accuracy of the proposed matching cost is twice higher than that of traditional NCC cost.

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[198]
Zhang L, 2013. Core topographical factor based investigation on the spatial pattern of loess terrain in the Loess Plateau [D]. Nanjing: Nanjing Normal University. (in Chinese)

[199]
Zhang L, Ai H B, Xu Bet al., 2017. Automatic tie-point extraction based on multiple-image matching and bundle adjustment of large block of oblique aerial images.Acta Geodaetica et Cartographica Sinica, 46(5): 554-564. (in Chinese)Due to advantages such as ease of interpretation,completeness through mitigation of occluding areas,as well as system accessibility,the aerial oblique images have found their place in numerous civil applications.However,for these applications high quality orientation data are essential.A fully automatic tie-point extraction procedure is developed to precisely orient the large block of oblique aerial images,in which a refined ASIFT algorithm and a window-based multiple-viewing image matching(WMVM)method are combined.In this approach,the WMVM method is based on the concept of multi-image matching guided from object space and allows reconstruction of 3Dobjects by matching all available images simultaneously,and a square correlation window in the reference image can be correlated with windows of different size,shape and orientation in the search images.Then another key algorithms,i.e.the combined bundle adjustment method with gross-error detection removal algorithm,which can be used for simultaneously orient the oblique and nearly-vertical images will be presented.Finally,through the experiments by using real oblique images over several test areas,the performance and accuracy of the proposed method is studied and presented.

[200]
Zhang L, Lu Y Q, 2013. Spatial analysis of the central place system based on accessibility.Scientia Geographica Sinica, 33(6): 649-658. (in Chinese)Based on the central place theory proposed by Walter Christaller,taking the shortest time and weighted average travel time as the accessibility evaluation index,using the accessibility calculation module as technical support based on the GIS platform,the spatial evolution and reconstruction of the central place system are explored from the aspects of spatial accessibility,spatial interactions,spatial scope of services under homogeneous background and transportation background.Through this way,formation process simulation and spatial expression of central place system are probed preliminary.The result shows that: Firstly,the secondary central place appears in the area which accessibility time is longest to the superior center under homogeneous background.Under the assumption of homogeneous plain,traffic in any direction are the same.The central place appears in the center of the hexagonal market area which accessibility is best and then present the concentric circles diffusion.With this diffusion,the time to the central place get longer.The secondary central places appear in the six vertices of hexagon whose accessibility time is the longest.And so on,the low level central place continue to appear until the production of the central place with the lowest level.Secondly,the accessibility based on weighted average travel time in the same level central place is not same.For same level central places,the closer to the high grade center place,the weighted average travel time is shorter.The same grade central place emerge the differences in growth.The closer to the high grade central place,the growth faster.With the increase of the grade and the quantity of central place,the difference of accessibility and centrality become more and more.As a result,continuous grade central places are formed.With the emergence of transit lines which connect central place,the accessibility of each grade central place is greatly raise.And the"Pole Axis System"is formed gradually.Finally,the spatial structure of central place system gets into a comprehensive organizational equilibrium stage which is composed of point,axis and network along with the traffic network evolution.

[201]
Zhang W, 2011. Research of catchment profile spectrum on northern Shaanxi Loess Plateau [D] Nanjing: Nanjing Normal University. (in Chinese)

[202]
Zhang W, Tang G A, Tao Yet al., 2011. An improved method to saddles extraction based on runoff concentration simulation in DEM.Science of Surveying and Mapping, 36(1): 158-159. (in Chinese)The saddle is one of the most important terrain feature points,the extraction of saddles based on DEMs is of significance to digital terrain analysis.Nevertheless,owning to saddles' unique morphological characteristic,it has more difficulties in extracting saddles than any other terrain feature points.This paper presented an improved saddles extraction method based on runoff concentration simulation in DEM.Firstly,the ridge lines were extracted by runoff concentration simulation in DEM.Then,inversed DEM were derived through overturning original landform to extract catchment lines,which can automatically divide the terrain.Finally,the saddles were extracted from intersecting feature lines.The experiments in different study areas demonstrated that this improved method considered the topological relationship between the saddles and surrounding terrain features,overcoming the disadvantage that the neighborhood analysis cannot take consideration of the whole terrain change.And the accuracy of saddles extraction was improved.

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[203]
Zhang X S, Hao F H, Cheng H Get al., 2004. Influence of subdivision of watershed on distributed hydrological model.Journal of Hydraulic Engineering, 735(7): 119-1237. (in Chinese)The distributed hydrological model-SWAT (Soil and Water Assessment Tool) is applied to analyze the influence of different watershed subdivisions on runoff yield and sediment yield. The result shows that: 1. the runoff yield will increase with the increase of subdivision amount and varies within a small range, but the sediment yield will decrease and varies significantly; 2. a critical subdivision level exists, the subdivision will not affect the runoff and sediment yield if the amount of subdivision exceeds this level. Furthermore, the influence of subdivision level, i.e. the spatial aggregation extent, on sediment yield is investigated by using the MUSLE (Modified Universal Soil Loss Equation). It is found that the term expressing the runoff in the equation is sensitively responding to the subdivision amount in the study area.

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[204]
Zhang Y, Fan H, Li Y E, 2013. A method of terrain feature extraction based on contour.Acta Geodaetica et Carto- graphica Sinica, 42(4): 574-580. (in Chinese)Abstract Terrain features include terrain feature points and terrain feature lines. They are basic object to analysis and processes of landscape, and the important contents of the structure generalization of landscape. A new method of contour-based terrain features lines extraction is proposed. Firstly, the contour lines are divided into two kinds of feature segments that include concave and convex segments, which corresponds to the valleys and ridges respectively, and using the maximum-angle as the constraint condition and using the edges of feature segments as the constraint edges, constrained Delaunay triangulation (referred to CDT) are constructed. Then, the skeletons of the CDT of every feature segment are traced and the local terrain structure line tree are constructed based on the obtained skeletons. And the leaf nodes of the terrain structure line trees are extracted and be treated as the terrain feature points of the corresponding feature segment. Finally, these terrain feature points are tracked and connected into terrain structure lines by applying the connecting criterion.

[205]
Zhang Z X, Zhang J Q, 1996. Digital photogrammetry [D]. Wuhan: Wuhan Technical University. (in Chinese)

[206]
Zhang Z X, Zhang J Q, 2005. Generalized point photogrammetry and its application.Geomatics and Information Science of Wuhan University, 30(1): 1-5. (in Chinese)Traditional point photogrammetry, line photogrammetry developed in the present and the infinite point theory are synthetized and sublined to the generalized point photogrammetry. After the theory of the generalized point photogrammetry is introduced, its applications are presented, including computer of image parameter from vanishing point and modelling by single image, determination of image parameters by matching between vector and image, inspection of sheet\|metal part and determination of plane pose by contour line matching.

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[207]
Zhang Z Y, Dong D D, Zhang G Xet al., 2017. Topographic constraints on the subduction erosion of the yap arc, western Pacific.Marine Geology & Quaternary Geology, 37(1): 41-50.

[208]
Zhang Z, Li J F, Chen Set al., 2011. Spatial distribution of affordable houses in cities: A case study of Wuhan based on DEM.Acta Geographica Sinica, 66(10): 1309-1320. (in Chinese)Affordable housing is associated with social welfare.The spatial location of affordable houses will determine the location of low-and medium-income households in cities,and thus urban social and economic development.The spatial location of affordable houses is concerned with site selection and social equity.A new concept-spatial welfare,and its method of calculation,are proposed.This paper uses Wuhan in Central China as an empirical case study.Spatial locations of affordable houses in this city are investigated by using GIS,DEM(Digital Elevation Model) and the concept of spatial welfare.A discussion of their site selection and spatial quality allocation in a microscopic view is presented in the end.

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[209]
Zhang Z, Song Z Y, Kong J, 2010. Wave-current interaction effects on velocity profiles and influencing factor analysis.Advances in Water Science, 21(6): 801-807.Abstract Many laboratory experiments on wave-current interaction have shown that a reduction in the current intensity is achieved when the wave propagate in the direction of the current, while the opposite is true when the current flowing in the opposite direction of the wave propagation. In this study, the expressions for the boundary shear stress and the velocity profile under the influence of wave-current interaction are derived to explain the laboratory-observed phenomena. The expressions are the Navier-Stokes equation based, which use the small amplitude wave theory assumption and incorporate with the Grant-Madsen model for wave-current bottom boundary layer flow. The result shows that our expressions are able to simulate the influence of wave height and viscosity on velocity profiles, and the simulation coincides with the observation. Also, our expressions are simple and practical compared to other wave-current models. Using the expressions, an influencing factor analysis is performed on the laboratory-observed phenomena, and the result is presented.

[210]
Zhao H J, Song Z Y, Xu F Met al., 2010. Numerical simulation of typhoon waves in the South China Sea: A case study of typhoon Chanchu.The Ocean Engineering, 28(3): 128-134. (in Chinese)With the driven wind incorporating the Myers typhoon model and the QSCAT/NCEP blended wind,a two-nested domain typhoon wave model is developed based on the third generation wave model SWAN.As a case study,typhoon Chanchu(0601) is selected to simulate waves from South China Sea to Guangdong province.Analysis of the numerical typhoon wave distribution in time and space is made and comparisons of the model data with those of observation by the Jason-1 satellite altimeter and the nearshore-located wave recorder show good results.It is concluded that the SWAN model could reasonably reproduce the features of typhoon waves in ocean and coastal waters spacially and temporally.

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[211]
Zhao H, Fang X, Ding Het al., 2017. Extraction of terraces on the Loess Plateau from high-resolution DEMs and imagery utilizing object-based image analysis.ISPRS International Journal of Geo-Information, 6(6): 157. (in Chinese)Abstract: Terraces are typical artificial landforms on the Loess Plateau, with ecological functions in water and soil conservation, agricultural production, and biodiversity. Recording the spatial distribution of terraces is the basis of monitoring their extent and understanding their ecological effects. The current terrace extraction method mainly relies on high-resolution imagery, but its accuracy is limited due to vegetation coverage distorting the features of terraces in imagery. High-resolution topographic data reflecting the morphology of true terrace surfaces are needed. Terraces extraction on the Loess Plateau is challenging because of the complex terrain and diverse vegetation after the implementation of egetation recovery . This study presents an automatic method of extracting terraces based on 1 m resolution digital elevation models (DEMs) and 0.3 m resolution Worldview-3 imagery as auxiliary information used for object-based image analysis (OBIA). A multi-resolution segmentation method was used where slope, positive and negative terrain index (PN), accumulative curvature slope (AC), and slope of slope (SOS) were determined as input layers for image segmentation by correlation analysis and Sheffield entropy method. The main classification features based on DEMs were chosen from the terrain features derived from terrain factors and texture features by gray-level co-occurrence matrix (GLCM) analysis; subsequently, these features were determined by the importance analysis on classification and regression tree (CART) analysis. Extraction rules based on DEMs were generated from the classification features with a total classification accuracy of 89.96%. The red band and near-infrared band of images were used to exclude construction land, which is easily confused with small-size terraces. As a result, the total classification accuracy was increased to 94%. The proposed method ensures comprehensive consideration of terrain, texture, shape, and spectrum characteristics, demonstrating huge potential in hilly-gully loess region with similarly complex terrain and diverse vegetation covers.

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[212]
Zhao M W, 2012. Research on the loess slope-landscape based on DEM [D]. Nanjing: Nanjing Normal University. (in Chinese)

[213]
Zhao M W, Li F Y, Tang G A, 2012. Optimal scale selection for DEM based slope segmentation in the Loess Pla- teau.International Journal of Geosciences, 3(1): 37-43.Optimal scale selection is the key step of the slope segmentation. Taking three geomorphological units in different parts of the loess as test areas and 5 m-resolution DEMs as original test date, this paper employed the changed ROC-LV (Lucian, 2010) in judging the optimal scales in the slope segmentation process. The experiment results showed that this method is effective in determining the optimal scale in the slope segmentation. The results also showed that the slope segmentation of the different geomorphological units require different optimal scales because the landform complexity is varied. The three test areas require the same scale which could distinguish the small gully because all the test areas have many gullies of the same size, however, when come to distinguish the basins, since the complexity of the three areas is different, the test areas require different scales.

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[214]
Zhao M W, Tang G A, Zhang Let al., 2012. The DEM based 5-node second-order finite difference model for slope computation. Journal of Geo-Information Science, 14(3): 286-291. (in Chinese)Slope is the most basic terrain parameter to construct geo-science models.The accuracy analysis of the computing model is one of the most important issues in the geo-science.A lot of studies focused on error analysis of the computing model over the past few decades.The source of the error and the relationship between the error and the other parameters were studied.However,few studies were aimed to put forward a new model to decrease the error,which is more important for high resolution DEMs.By analyzing the error source of the slope computing model,this paper put forward a new model called 5 Node Second-order Finite Difference(5N-2FD).The characteristic of this model is that it is able to consider the multi-distance neighbor node: firstly it builds two difference models using different grid sizes,and then combines the two models into one with different weights.It is proved that it can improve the accuracy of the results remarkably through mathematical analysis.In this paper,a mathematical surface is selected to verify the accuracy of the new model.In order to study the influence of the resolution to the accuracy of the slope,this paper generated DEMs from the mathematical surface with different resolution,one is 1m,and the other is 5m.The results show that the new model can significantly improve the accuracy of the result compared with the common models.This study enriched the method system of digital terrain analysis,and provided slope data of high accuracy for many geo-science models.In addition,besides slope,there are many terrain parameters which are calculated through finite difference,such as aspect and various kinds of curvature,and the methods of this paper could afford some useful references in improving the accuracy of such terrain parameters.

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[215]
Zhao S M, Cheng W M, Chai H Xet al., 2007. Research on the information extraction method of periglacial geomorphology on the Qinghai-Tibet based on remote sensing and SRTM: A case study of 1B1,000,000 Lhasa map sheet (H46).Geographical Research, 26(6): 1175-1185. (in Chinese)

[216]
Zhao S M, Cheng W M, Zhou C Het al., 2009. Analysis on the topographic gradient and geographical meaning of Mt. Konggur, in the northern edge of Qinghai-Tibet Plateau.Journal of Geo-information Science, 11(6): 753-758.Taking Mt.Konggur,of West Kunlun Mountains in the northern edge of Qinghai-Tibet Plateau as an experiment area,utilizing the digital elevation model data acquired by Space Shuttle RadarTerrain Mission(SRTM),this paper makes a research on the topographic gradient from Mt.Konggur to Tarim Basin using the methods of linear terrain profile and swath terrain profile.This research not only probes into the relation between the topographic gradient and uplifting process in the experiment area,but also makes a comparison between linear terrain profile and swath terrain profile.Research results show that:(1)Linear terrain profile is clear,readable and has simple process;whereas,swath terrain can represent the topographic relief condition in the area.Hence,the effect will be better if we study the topography by combining these two methods.(2)From Tarim Basin to the peak of Mt.Konggur,the elevation rise can be divided into 3 gradients: from 2 000m to about 4 500m,from 4 500m to about 6 000m,and from about 6 000m to about 7 500m.The different gradient of elevation rise perhaps corresponds to the different uplift process in the geomorphologic evolving process of Mt.Konggur in Late Cenozoic;the inflexion of every elevation rise gradient may be the dividing point of different uplift process.

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[217]
Zhao W D, Xu Y, Ma Let al., 2013. Research on the terraces-considered grid-TIN hybird mesh DEM.Geography and Geo-Information Science, 29(2): 11-16. (in Chinese)The concept and data model of a new terraces-considered Grid-TIN based DEM(GT-DEM) are put forth on the basis of object-oriented thought to solve the problem that the terraces terrains on loess plateau are difficult to be represented by grid-based DEM,and its main characteristics and the relationship with traditional DEM are also clarified.Taking the level terraces in the Xindiangou small watershed of Suide County in Shaanxi Province as example,this paper constructs terraces-considered GT-DEM successfully by use of 1 10 000 grid-based DEM and feature points and lines of terraces and its outer boundary.The study shows that it is technically feasible to construct terraces-considered GT-DEM by use of grid-based DEM and feature points and lines of terraces and its outer boundary.Not only the global terrains of study areas can be represented roughly by GT-DEM,the local terraces terrains can also be represented refinedly by it.This research is useful exploration for improving the abilities of DEM for the digital representation of terraces terrains and will be of great importance in improving the abilities of DEM for the digital representation of other artificial terrains like check-dams and fish-scale pits in the future.

[218]
Zhao Y J, Lin C Y, 2010. Multi-condition constraint geological modeling based on seismic data.Computer Appli- cations of Petroleum, (2): 17-20 (in Chinese)

[219]
Zhen Y, Liu X J, Wang M Z, 2014. An improved RANSAC of fundamental matrix estimation method.Bulletin of Surveying and Mapping, (4): 39-43. (in Chinese)

[220]
Zheng S Y, Zhou Y, 2012. High quality texture reconstruction for small objects based on structure light scanning system with digital camera.Geomatics and Information Science of Wuhan University, 37(5): 529-533. (in Chinese)3D models with high quality and realistic texture is a very significant topic in the field of digital museum,heritage conservation,and so on.For the small bronze artifact Shuangniaotaotiewenkushentuogu and other small objects,we propose a new texture reconstruction method of high-automation,high-efficient,and high-quality.Based on the structure light scanning system with common digital camera,our approach mainly resolved the registration for a single high-resolution image,and the seamless texture generation from multi-view images.Massive reconstruction tests proved the feasibility and validity of this method.

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[221]
Zhong D H, Li M C, Liu J, 2007. Research on the three-dimensional unified modeling method for hydraulic and hydropower engineering. Scientia Sinica Technologica, 37(3): 455-466. (in Chinese)

[222]
Zhong T, Tang G A, Zhou Yet al., 2009. Method of extracting surface peaks based on reverse DEMs.Bulletin of Surveying and Mapping, 4: 35-37. (in Chinese)

[223]
Zhou L C, Chen S Z, Zhu Y, 2007. 3D-volume visualization research for geological structure.Application Re- search of Computers, 24(6): 150-164.A method of 3D modeling and visualization of geological structures was proposed. It fuses basic geography data,bore data and section data of interpretation of geophysical exploration,builds three-dimensional spatial data field model by spatial interpolation technique and carries out the volume visualization by 3D texture hardware assisted direct volume rendering technique.The spatial distribution and inner attribute of stratum are reflected by real 3D.

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[224]
Zhou L C, Lin B X, Wang Det al., 2013. 3D geological modeling method based on planar Geological Ma.Journal of Geo-Information Science, 15(1): 46-54. (in Chinese)For a long time,the study of 3D geological modeling relies on using exploration data from drill holes or geologic sections.But,on the premise of the lack of large area general geological background modeling,only considering of local region refined modeling often lead to overgeneralization and over-reliance on the data.Plane geological map,which integrates geological field survey and the results of the work with geological expert knowledge,reveals rock stratigraphy and geological structure of the region,is the available and the most direct data source for 3D geological modeling.On the premise of the lack of other geological data,using planar geological map to build 3D geological model is an effective solution.The 3D geological modeling directly based on planar geological map,but it is weak in controllability and the building quality of the geological models is unsatisfactory.To solve this problem,this article proposed a new 3D geological modeling method based on geological plane maps and used cutting profile as the intermediary.The method encrypted the existing data of the study area indirectly,processed complex structures such as folds using cubic spline fitting combining with artificial revision,and realized the automatic drawing of cutting profile based on the geological plane maps.We took regular voxels as the 3D spatial data model,got a series of parallel cutting profile of the study area automatically drawn,and built a rasterized 3D geological model.With Xinggang area,Chongqing City as the study area,the prototype experiment system was built and we verified the effectiveness and practicality.Results showed that the 3D geological modeling method based on geological plane maps is an effective solution to build regional 3D geological model under the condition of lacking of other geological data.

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[225]
Zhou Q, 2013. Analysis of how the earth’s landscape form Now exploring the Mystery of the “Plate”.Friend of Science Amateurs, 11: 123-128.

[226]
Zhou Q, PILESJÖ P, Chen Y, 2011. Estimating surface flow paths on a digital elevation model using a triangular facet network.Water Resources Research, 47(7): 1772-1780.This study attempts to develop a method for the simulation of surface flow paths on a digital elevation model (DEM). The objective is to use a facet-based algorithm to estimate the surface flow paths on a raster DEM. A grid DEM was used to create a triangular facet network (TFN) over which the surface flow paths were determined. Since each facet in the network has a constant slope and aspect, the estimations of, for example, flow direction and divergence/convergence are less complicated compared to traditional raster-based solutions. Experiments were undertaken by estimating the specific catchment area (SCA) over a number of mathematical surfaces, as well as on a real-world DEM. Comparisons were made between the derived SCA by the TFN algorithm with some algorithms reported in the literature. The results show that the TFN algorithm produced the closest outcomes to the theoretical values of the SCA compared with other algorithms, deriving more consistent outcomes and being less influenced by surface shapes. The real-world DEM test also shows that the TFN was capable of modeling flow distribution without noticeable "artifacts," and its ability of tracking flow paths makes it an appropriate platform for dynamic surface flow simulation.

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[227]
Zhou Q M, Liu X J, 2006. Digital Terrain Analysis. Beijing: Science Press. (in Chinese)

[228]
Zhou Y, Tang G A, Wang Cet al., 2010. Automatic segmentation of loess positive and negative terrains based on high resolution grid DEMs.Scientia Geographica Sinica, 30(2): 261-266. (in Chinese)China Loess Plateau is world-wide famous for its peculiar and unique landscape, in which the loess shoulder-lines zigzag on the surface making a distinct separation between loess positive terrain and the negative one. The automatic segmentation of loess positive and negative terrains (P-N terrains) with precise location and high efficiency, which is a crucial technique in constructing the mechanism-process models of loess landform drainage systems, is still need to be further improved. Nowadays, with the increasing availability of digital topographic data, the Digital Elevation Model (DEM) can now be applied to better description of natural topography, and it is also regarded as the most proper data source for automatic extraction of loess positive and negative terrains. In this paper, the conformation and flow confluence characteristic of the hill-slope in representative loess landforms is discussed. Based on this, an auto-segmentation method of P-N terrains from 5 m resolution DEMs is proposed. There are three key procedures in the operation. The first step is the identification of grid points on the shoulder-line position by considering the slope difference up and down. Slope gradient 30 ,25 and 20 are used as the thresholds in loess platform area, loess ridge-hill area and loess hill area respectively in the extraction model. The second stage is to expand shoulder-lines candidate cells directionally by considering the spatial direction of the local hill slope aspect and the trend of the shoulder-lines. This step is helpful for deriving more consecutive and detailed shoulder-lines on DEMs. The third step is the generation of positive terrain which can be regarded as the extraction of the upstream area of the shoulder-line points by using the hydrologic analysis model. All the shoulder-lines cells derived above are imported into the model as the pour point data. This is an alternative method for evading the difficulty of converting shoulder-line grid cells into consecutive vector lines. Validation tests are took out by contrasting the auto-extraction results from DEMs and the delineating results from 1 m resolution DOMs in six drainages. Results show that maximum area difference between the positive terrain area derived above and actural area is 1.15 km2, and the percentage of the cells distance offset values less than 10 m exceed 95%. So the main advantages of this approach are high accuracy, lower demands on manual intervention and ready availability of required data for many regions on the Loess Plateau. The morphology of the earth surface is the interactional production of the hydrosphere, lithosphere, atmosphere and the biosphere, thus the morphology is the external representation, and the interaction process is the inner dynamical force. The extraction of the topographic feature lines not only need considering the characteristic of the terrain morphology, but also need considering the inner mechanism of land surface process.

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[229]
Zhou Y, Tang G A, Xi Yet al., 2013. A shoulder-lines connection algorithm using improved snake model.Geo- matics and Information Science of Wuhan University, 38(1): 82-85. (in Chinese)A novel method for automatic connection of Loess shoulder-lines using improved Snake model is designed in this paper.Firstly,according to the morphological characteristics of loess hillslope,raster points on the position of shoulder-lines are detected based on high resolution DEM data.Then buffer curve of divide line sets as the initial Snake curve.Thirdly,the gradient vector flow field,as core parameter in Snake model,is modified by hillslope flow direction field.Finely Snake curve is forced to creep to shoulder-line points under the guidance of the modified Snake model to make a continuous shoulder line,which is the division of P-N terrains.Segmentation experiments show the continuity and precision of results meet our need and have good agreement with the real topography.

[230]
Zhou Y, Tang G A, Yang Xet al., 2010. Positive and negative terrains on northern Shaanxi Loess Plateau.Journal of Geographical Sciences, 20(1): 64-76.The Loess positive and negative terrains (P-N terrains), which are widely distributed on the Loess Plateau, are discussed for the first time by introducing its characteristic, demarcation as well as extraction method from high-resolution Digital Elevation Models. Using 5 m-resolution DEMs as original test data, P-N terrains of 48 geomorphological units in different parts of Shaanxi Loess Plateau are extracted accurately. Then six indicators for depicting the geomorphologic landscape and spatial configuration characteristic of P-N terrains are proposed. The spatial distribution rules of these indicators and the relationship between the P-N terrains and Loess relief are discussed for further understanding of Loess landforms. Finally, with the integration of P-N terrains and traditional terrain indices, a series of un-supervised classification methods are applied to make a proper landform classification in northern Shaanxi. Results show that P-N terrains are an effect clue to reveal energy and substance distribution rules on the Loess Plateau. A continuous change of P-N terrains from south to north in Shaanxi Loess Plateau shows an obvious spatial difference of Loess landforms and the positive terrain area only accounted for 60.5% in this region. The P-N terrains participant landform classification method increases validity of the result, especially in the Loess tableland, Loess tableland-ridge and the Loess low-hill area. This research is significant on the study of Loess landforms with the Digital Terrains Analysis methods.

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[231]
Zhou Y, Tang G A, Zhang Tet al., 2007. A new method for the derivation of terrain skeleton lines based on wire-like analysis window in grid DEMs.Bulletin of Surveying and Mapping, 10: 67-69. (in Chinese)

[232]
Zhou Z P, Cheng W M, Wan Cet al., 2012. Analysis of spatial distribution characteristics of lunar near side impact craters. Journal of Geoinformation Science, 14(5): 618-626. (in Chinese)The mathematical statistics and spatial analyses for lunar near side impact craters are used to unravel potential spatial heterogeneity based on the crater nomenclature released by International Astronomical Union (IAU) and topography and imagery data from Chang'E-1(CE-1).The spatial heterogeneity is mainly embodied in the following aspects: (1)the craters with larger diameters dominantly distribute in the highland and show obvious concentration tendency, however, the mare have much fewer larger craters, accompanying by munificent smaller craters; (2) larger craters have the characteristics of randomness and the smaller crater are concentrated in local areas; (3) density differences: the regions closer to equator have higher crater frequencies than the regions to the pole; the trailing hemisphere is cratered at a higher rate than the leading hemisphere; the most densely cratered region is located in the south-central part of the lunar nearside; (4) depth-diameter ratios differences: the craters with depth larger than 2.5 km almost are found in the highland, and there is a marked concentration of points around the central meridian where it cuts through the southern continent; between 57 N and 24 S, the ratio is at a high level; the maximum value occurs near 14 N, and the average value fluctuates at 0.14; approaching the poles, the ratios are becoming smaller, and the minimum value occurs at the south pole region; and (5) gradient differences: the average of crater's maximum gradient in highland is far greater than the value of craters in mare; the average of crater's maximum gradient shows apparent pattern: from lunar equator to the poles, the average of crater maximum gradient increases gradually. The spatial pattern of lunar craters shows marked regional differentiation characteristics, and the relationship between the pattern and the crater forming theory remains much work to be done before the ultimate goal can be reached.

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[233]
Zhou Z P, Cheng W M, Zhou C Het al., 2011. Characteristic analysis of the lunar surface and automatically ex- tracting of the lunar morphology based on CE-1.Chinese Science Bulletin, 56(1): 18-26. (in Chinese)The satellite Chang’E-1(CE-1) was launched in October 24, 2007 in China, which obtained a large number of scientific data of the global moon, including imageries and laser altimetric data. In this paper, the characteristics of the lunar surface are analyzed and the lunar morphologic information of the lunar mare and highland is automatically extracted based on the imagery acquired by CCD camera and the DEM processed by three-line digital photogrammetric technology. The results show that the average elevation of the global moon is –742 m; the highest and lowest locations stand in the farside of the moon; the highest is at the eastern margin of Engel’gardt crater; the lowest is in the secondary impact crater pit of Minkowski crater. The surface of the moon is very flat; most of its slope is bellow 15°, accounting for 90% of the total area of the global moon. The great variation of slope value mainly distributes in the lunar highlands, with an average slope of greater than 7°. The lunar mares widely distribute in the nearside of moon, with an average slope of below 3°. The optimum statistical unit for lunar relief value is 16 km2. The mare and highland are the basic types of lunar morphology, which can be automatically extracted by maximum likelihood classifier based on the elevation data and slope, relief and imagery data. The values of altitude, slope, relief and grey level of CE-1 imageries are normalized and binarized. A case study of H010 (locating in 0°–18°W, 0°–14°S) shows that the overall accuracy assessment for extracted results of the lunar mare and highland based on the geological data published by USGS in 1971 is better, and the Kappa coefficient is 0.78, and the results of the lunar mare and highland show that the method can be used to extract the characteristics of lunar surface.

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[234]
Zhu A X, Wang R, Qiao Jet al., 2014. An expert knowledge-based approach to landslide susceptibility mapping using GIS and fuzzy logic.Geomorphology, 214(214): 128-138.This paper presents an expert knowledge-based approach to landslide susceptibility mapping in an effort to overcome the deficiencies of data-driven approaches. The proposed approach consists of three generic steps: (1) extraction of knowledge on the relationship between landslide susceptibility and predisposing factors from domain experts, (2) characterization of predisposing factors using GIS techniques, and (3) prediction of landslide susceptibility under fuzzy logic. The approach was tested in two study areas in China — the Kaixian study area (about 25002km 2 ) and the Three Gorges study area (about 460002km 2 ). The Kaixian study area was used to develop the approach and to evaluate its validity. The Three Gorges study area was used to test both the portability and the applicability of the developed approach for mapping landslide susceptibility over large study areas. Performance was evaluated by examining if the mean of the computed susceptibility values at landslide sites was statistically different from that of the entire study area. A z -score test was used to examine the statistical significance of the difference. The computed z for the Kaixian area was 3.70 and the corresponding p -value was less than 0.001. This suggests that the computed landslide susceptibility values are good indicators of landslide occurrences. In the Three Gorges study area, the computed z was 10.75 and the corresponding p -value was less than 0.001. In addition, we divided the susceptibility value into four levels: low (0.0–0.25), moderate (0.25–0.5), high (0.5–0.75) and very high (0.75–1.0). No landslides were found for areas of low susceptibility. Landslide density was about three times higher in areas of very high susceptibility than that in the moderate susceptibility areas, and more than twice as high as that in the high susceptibility areas. The results from the Three Gorge study area suggest that the extracted expert knowledge can be extrapolated to another study area and the developed approach can be used in large-scale projects. Results from these case studies suggest that the expert knowledge-based approach is effective in mapping landslide susceptibility and that its performance is maintained when it is moved to a new area from the model development area without changes to the knowledge base.

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[235]
Zhu H C, Tang G A, Wu L Cet al., 2012. Extraction and analysis of gully nodes based on geomorphological structures and catchment characteristics: A case study in the Loess Plateau of north Shaanxi province.Advances in Water Science, 23(1): 7-13. (in Chinese)A gully node is the intersection of gully or river networks,which reflects the geomorphological structure and hydrological characteristic of the gully area.Effective extraction and analysis of gully nodes are essential to understand the spatial structure,morphology,and hydrological characteristic of a catchment.An algorithm based on high resolution digital elevation model(DEM) data is proposed for extracting gully nodes together with the classification method.The algorithm and method are tested in an experimental area on the Loess Plateau of North Shaanxi Province.The numbers of gully nodes of different order gullies and the flow accumulation value associated with each gully node are obtained.The relationship between the numbers of gully nodes in any given order class and the sum of corresponding flow accumulation values is obtained using a mathematical model.The variations in the spatial distribution of flow accumulation values in different geomorphological regions are studied using the arithmetic progression classification method.Finally,the spatial regularity of geomorphological features is preliminary discussed.

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[236]
Zhu H C, Tang G A, Zhang Y Set al., 2003. Thalweg in loess hill area based on DEM.Bulletin of Soil and Water Conservation, 23(5): 43-45. (in Chinese)The thalweg in loess hill area is an important terrain structural line, reflecting topography and landform character. A case study is conducted in Jiuyuan valley of Suide county, north Shaanxi province. The principles and methods of distilling automatically thalweg are discussed in the context of a DEM, and the precision of results relative to charts and terrain maps is analyzed. The study shows that the technology and method of distilling the thalweg using DEM are practical and effective.

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[237]
Zhu L F, Wu X C, Liu X Get al., 2004. Introduction and implementation of virtual borehole in the construction of urban 3D strata model.Geography and Geo-Information Science, 20(6): 26-30. (in Chinese)Engineering borehole data is the primary data source for the reconstruction of urban 3D strata model.For a given study area,sometimes it is impossible to construct an integrated,accurate 3D model based on limited sample data obtained from boreholes,which are usually sparse and scattered.To solve this problem,a conceptual model called virtual borehole is presented.In the process of modeling,several virtual boreholes can be acceded to the 3D strata model on the proper position for the user's demand and comprehension of the geologic model.Virtual boreholes restrict the model just as actual boreholes,and then generate a 3D solid strata model which is accurate and subtle.A case study is presented to compare the practical effects of using and not using virtual borehole.The result shows that it is flexible,visual and operable of using virtual borehole in the 3D strata modeling.

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[238]
Zhu S J, Tang G A, Li F Yet al., 2013. Spatial variation of hypsometric integral in the Loess Plateau based on DEM.Acta Geographica Sinica, 68(7): 921-932. (in Chinese)Hypsometric integral is a terrain analysis factor with apparent physical and geomorphologic meanings which could reflect the landform erosion stage and evolution process.As a macroscopic parameter and method in terrain analysis,the applications of hypsometric integral could reveal the quantitative characteristic of landform evolution in catchment scale.In this paper,5 m resolution DEMs and 3 arc-second resolution SRTM DEMs are used respectively to identify the impact factors of HI and its spatial variation in the Loess Plateau.Firstly,the geomorphologic meaning is discussed and summarized.The effect of DEM resolution and the analysis area in HI calculating is probed.With different DEM resolutions,the HI values derived could keep almost the same.When the area of catchment reaches 10 km2,the HI tends to be stable,which is regarded as a critical area for extracting HI in this study.Then,the geomorphic feature HI is proposed and the correlation of each kind of HI is calculated.There exist two feature groups in which the correlation coefficient is rather large.They are respectively catchment HI,positive terrain HI,shoulder line HI and peak HI,ridge line HI,and catchment boundary HI.Finally,the landform division based on HI is created through multiresolution segmentation in loess area.The coupling relationships exist in this division and water soil loss map,sediment transport value map.The division in this paper refines the original map to a certain extent.

[239]
Zhu S J, Tang G A, Zhang Wet al., 2011. Rapid modeling method for terrace digital elevation model.Bulletin of Surveying and Mapping, (4): 68-70. (in Chinese)

[240]
Zhu Y J, 2011. GIS-based analysis of the accessibility of urban forests in the central city of Guangzhou, China.Acta Ecologica Sinica, 31(8): 2290-2300. (in Chinese)The concept of urban forestry was created as early as in 1894 in the United States,and developed in 1960s quickly in North America and Europe.The concept of urban forestry was introduced to china in the 1980s,and Chinese scholars paid more attention on the aspects of urban forest functions and benefits previously,but rarely studied their service ability were,which was concerned more by foreign scholars.In China,the current criterion that have evaluated the service ability of urban forest often employed some statistical indices such as coverage rate,coverage area per capita,and numbers of urban forest as well.Whether to acquire the "natural services" of urban forests is the basic requirements of urban forest functions,a guide line of life quality of urban residents,and an important aspect of city modernization and international competitiveness as well.The access to urban forests for urban residents could be used as an index to evaluate the implementation of urban forest functions.As the main element of the ecological landscape,urban forests are the principal part of ecological constructions in urban regions.The blocks were an essential composition of an urbanized area.The network analyst model in ArcGIS9.2 was used to analyze the accessibility between the blocks and urban forest patches within Outer Ring Highway in Guangzhou,and the service capacity of urban forest patches was examined as well.The differences among the blocks were analyzed in combination with tree canopy coverage by interpretation of aerial photos. The results showed that 73% of the blocks could reach large green patchs in a 2km walk distance,and about 46% in a 1km walk distance,but only 18% of blocks could reach large green patchs in a 0.5km walk distance.Urban forest patches accessibility was the highest in Yuexiu District,while the provision and accessibility were the most inadequate and worst in Fangcun and Haizhu Districts.Among blocks that could not reach large green patch in a 0.5km walk distance but tree canopy coverage beyond 30%,the percent of institutions block was predominant,while the coverage of most of the resident blocks was under 10%,and even 64% of those under 5%. Though the actual distance might be over-estimated or under-estimated due to the use of centroids as the blocks,the losses and gains were balanced within the 2169 blocks and the uncertainty was assumed to be negligiblein this analysis.The results indicated that the total service area of urban forests was smaller than the area derived by the conventional simple buffering method,and this was due to the fact that the actual pedestrian routes were not direct and affected by many factors.GIS-based network analyses offered a more realistic insight into actual provision of urban forest and were able to reliably identify the location of lacking urban forest services and inform the local planning process.Combining the actual pedestrian accessibility rather than buffers or straight lines to urban forests with the tree canopy coverage of blocks,the results derived from the Network Analyst Model using block units provided valuable information for urban forest landscape pattern optimization at a small scale in Guangzhou.

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