地理信息系统导论chap13

1、Chapter 13. TERRAIN MAPPING AND ANALYSIS13.1 Data for Terrain Mapping and Analysis13.1.1 DEMBox 13.1 An Application Example of LIDAR DEM13.1.2 TIN13.2 Terrain Mapping13.2.1 Contouring13.2.2 Vertical Profiling13.2.3 Hill ShadingBox 13.2 The Pseudoscopic EffectBox 13.3 A Worked Example of Computing Re

2、lative Radiance13.2.4 Hypsometric Tinting13.2.5 Perspective View13.3 Slope and Aspect13.3.1 Computing Algorithms for Slope and Aspect Using RasterBox 13.4 Conversion of D to AspectBox 13.5 A Worked Example of Computing Slope and Aspect Using Raster13.3.2 Computing Algorithms for Slope and Aspect Usi

3、ng TINBox 13.6 A Worked Example of Computing Slope and Aspect Using TIN13.3.3 Factors Influencing Slope and Aspect Measures13.4 Surface CurvatureBox 13.7 A Worked Example of Computing Surface Curvature13.5 Raster Versus TINKey Concepts and TermsReview QuestionsApplications: Terrain Mapping and Analy

4、sisTask 1: Use DEM for Terrain MappingTask 2: Derive Slope, Aspect, and Curvature from DEMTask 3: Build and Display a TIN Challenge TaskReferencesData for Terrain Mapping and AnalysisnDEM (digital elevation model) and TIN (triangulated irregular network) are two common types of input data for terrai

5、n mapping and analysis.nA DEM represents a regular array of elevation points. It can be converted to an elevation raster by placing each elevation point at the center of a cell. The USGS offers DEMs in three spatial resolutions: 1 arc-second (30 m), 1/3 arc-second (10 m), and 1/9 arc-second (3 m). A

6、dditionally, LIDAR data are increasingly being used for studies that require detailed topographic data.nA TIN approximates the land surface with a series of nonoverlapping triangles. Raster/TIN ConversionnThe maximum z-tolerance algorithm selects points from an elevation raster to construct a TIN su

7、ch that, for every point in the elevation raster, the difference between the original elevation and the estimated elevation from the TIN is within the specified maximum z-tolerance.nA TIN can be converted into a DEM by using local first-order polynomial interpolation.Input Data to TINBesides DEM, a

8、TIN can also use additional point data such as surveyed elevation points, GPS (global positioning system) data, and LIDAR data; line data such as contour lines and breaklines; and area data such as lakes and reservoirs.Figure 13.1A breakline, shown as a dashed line in (b), subdivides the triangles i

9、n (a) into a series of smaller triangles in (c).Terrain MappingTerrain mapping techniques include contouring, vertical profiling, hill shading, hypsometric tinting, and perspective (3-D) view.Figure 13.2A contour line map.Figure 13.3The contour line of 900 connects points that are interpolated to ha

10、ve the value of 900 along the triangle edges.Figure 13.4A vertical profile.Figure 13.5An example of hill shading, with the suns azimuth at 315 (NW) and the suns altitude at 45.Figure 13.6A hypsometric map. Different elevation zones are shown in different gray symbols.Figure 13.7A 3-D perspective vie

11、w. Figure 13.8Three controlling parameters of the appearance of a 3-D view: the viewing azimuth a is measured clockwise from the north, the viewing angle u is measured from the horizon, and the viewing distance d is measured between the observation point and the 3-D surface. The fourth parameter z-s

12、cale, or the vertical exaggeration factor, is not shown in the figure.Parameters Controlling the Appearance of a 3-D ViewFigure 13.9Draping of streams and shorelines on a 3-D surface.3-D DrapingFigure 13.10A 3-D perspective view of an elevation zone map.Figure 13.11A view of 3-D buildings in Boston,

13、 Massachusetts.Slope and AspectnSlope measures the rate of change of elevation at a surface location. Slope may be expressed as percent slope or degree slope. nAspect is the directional measure of slope. Aspect starts with 0 at the north, moves clockwise, and ends with 360 also at the north. Because

14、 it is a circular measure, We often have to manipulate aspect measures before using them in data analysis. Figure 13.12Slope, either measured in percent or degrees, can be calculated from the vertical distance a and the horizontal distance b. Figure 13.13Aspect measures are often grouped into the fo

15、ur principal directions (top) or eight principal directions (bottom).Figure 13.14Transformation methods to capture the NS direction (a), the NESW direction (b), the EW direction (c), and the NWSE direction (d).Computing Algorithms for Slope and Aspect Using RasternThe slope and aspect for an area un

16、it (i.e., a cell or triangle) are measured by the quantity and direction of tilt of the units normal vectora directed line perpendicular to the unit.nDifferent approximation (finite difference) methods have been proposed for calculating slope and aspect from an elevation raster. Usually based on a 3

17、-by-3 moving window, these methods differ in the number of neighboring cells used in the estimation and the weight applying to each cell. Figure 13.15The normal vector to the cell is the directed line perpendicular to the cell. The quantity and direction of tilt of the normal vector determine the sl

18、ope and aspect of the cell. (Redrawn from Hodgson, 1998, CaGIS 25, (3): pp. 173185; reprinted with the permission of the American Congress on Surveying and Mapping.)Figure 13.16Ritters algorithm for computing slope and aspect at C0 uses the four immediate neighbors of C0.Figure 13.17Horns algorithm

19、for computing slope and aspect at C0 uses the eight neighboring cells of C0. The algorithm also applies a weight of 2 to e2, e4, e5, and e7, and a weight of 1 to e1, e3, e6, and e8. Computing Algorithms for Slope and Aspect using TINThe x, y, and z values of points that make up a TIN are used to com

20、pute slope and aspect for each triangle. Figure 13.18The algorithm for computing slope and aspect of a triangle in a TIN uses the x, y, and z values at the three nodes of the triangle. Factors Influencing Slope and Aspect MeasuresFactors that can influence slope and aspect measures include the resolution of DEM, the quality of DEM, the computing algorithm, and local topography.Figure 13.19DEMs at t