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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)

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introduction
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
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 analysis4
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 analysis5
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
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 mapping7
Terrain Mapping
  • Vertical profile shows changes in elevation along a line, such as a hiking trainl, road or stream.
terrain mapping8
Terrain Mapping
  • Hill shading is also known as a shaded relief or simply shading
  • 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 mapping9
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 mapping10
Terrain Mapping
  • Hypsometric tinting
    • Applies different color symbols to represent elevation zones.
terrain mapping11
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
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 analysis13
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 analysis14
Terrain Analysis
  • Watershed analysis
    • Requires three data sets in raster format
    • Filled elevation grid
    • Flow direction grid
    • Flow accumulation grid
grid vs tin
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 tin16
Grid vs TIN
  • Computational efficiency with grid
  • TIN gives sharper image
  • How are they built and used?