Terrain Mapping and Analysis

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# Terrain Mapping and Analysis - PowerPoint PPT Presentation

Terrain Mapping and Analysis. Chapter 12. Introduction. Terrain mapping Land surface is 3-D Elevation data or z-data is treated as a cell value or a point data attribute rather than as a coordinate. Data for Terrain Mapping and Analysis. Digital Elevation Model (DEM)

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## Terrain Mapping and Analysis

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### Terrain Mapping and Analysis

Chapter 12

Introduction
• Terrain mapping
• Land surface is 3-D
• Elevation data or z-data is treated as a cell value or a point data attribute rather than as a coordinate.
Data for Terrain Mapping and Analysis
• Digital Elevation Model (DEM)
• Array of elevation points
• 7.5 minute USGS quads into 4 levels
• Level 1 RMS 7-15 meters
• Level 2 RMS of ½ contour interval
• Level 3 RMS of 1/3 contour interval not to exceed 7 meters
• What happened to Level 4?
• Relative and absolute errors
Data for Terrain Mapping and Analysis
• Triangulated Irregular Network (TIN)
• Series of non-overlapping triangles
• Elevation values are stored at nodes
• Irregular distribution
• Sources: DEMs, surveyed elevation points, contour lines, and breaklines
• Breaklines are line features that represent changes of the land surface such as streams, shorelines, ridges, and roads
Data for Terrain Mapping and Analysis
• Triangulated Irregular Network (TIN)
• Not every point in DEM is used
• Only points most important
• VIP (Very Important Points) algorithm
• Maximum z-tolerance algorithm
• Delaunay triangulation: all nodes are connected to their nearest neighbor to form triangles which are as equi-angular as possible.
• Borders are a problem
• Go beyond study area and clip to make best
Terrain Mapping
• Contouring is most common method for terrain mapping
• Contour lines connect points of equal elevation (isolines)
• Contour intervals represent the vertical distance between contour lines.
• Arrangement of contour lines reflect topography
Terrain Mapping
• Vertical profile shows changes in elevation along a line, such as a hiking trainl, road or stream.
Terrain Mapping
• Attempts to simulate how the terrain looks with the interaction between sunlight and surface features.
• Helps viewers recognize the shape of land-form features on a map.
• Digital shaded-relief map of US
Terrain Mapping
• Four factors control the visual effect of hill-shading
• Sun’s azimuth is direction of incoming light (0 to 360°)
• The sun’s altitude from horizon (0-90°)
• Surface slope (0-90°)
• Surface aspect (0 to 360°)
Terrain Mapping
• Hypsometric tinting
• Applies different color symbols to represent elevation zones.
Terrain Mapping
• Perspective View
• Perspectives are 3-D views of the terrain wherein the appearance is as viewed from an airplane.
• Viewing azimuth (0 to 360°)
• Viewing angle (0-90°)
• Viewing distance
• Z-scale is ratio between he vertical scale and the horizontal scale (exaggeration factor)
• 3-D draping of vector information
Terrain Analysis
• Slope measures the rate of change of elevation at a surface location
• Aspect is the directional measure of the slope (degrees- 4 or 8 directions)
• Important for analyzing an visualizing landform characteristics
• Accuracy an issue
• If you want to try, use the worked examples in the text with Excel
Terrain Analysis
• Surface curvature: convex or concave
• Viewshed analysis
• Viewshed refers to the areas of the land surface that are visible from an observation point or points.
• Watershed analysis
• Watershed is an area that drains water and other substances to a common outlet
Terrain Analysis
• Watershed analysis
• Requires three data sets in raster format
• Filled elevation grid
• Flow direction grid
• Flow accumulation grid
Grid vs TIN
• Different algorithms and type of output
• Can be converted from TIN to grid or grid to TIN
• TIN has flexibility of input sources: DEM, breaklines, contour lines, GPS data and survey data as well as user added elevation points.
• Elevation grid is fixed with a given cell size
Grid vs TIN
• Computational efficiency with grid
• TIN gives sharper image
• How are they built and used?