Geographic Information Systems Digital Elevation Models (DEM)
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Transcript of Geographic Information Systems Digital Elevation Models (DEM)
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Geographic Information Geographic Information SystemsSystems
Digital Elevation Models (DEM)Digital Elevation Models (DEM)
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1. Digital Elevation 1. Digital Elevation ModelModel
► A set of elevation measurements for locations distributed over the land surface
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2. Basic Methods to 2. Basic Methods to Capture and Store DEM Capture and Store DEM
DataData► Regular gridsRegular grids► ContoursContours► ProfilesProfiles► Triangulated irregular network (TIN) Triangulated irregular network (TIN)
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► The elevation values are stored as a matrix of regularly spaced ground positions ► Each data point represents the elevation of the grid cell in which it is located
2. (1) Regular Grids2. (1) Regular Grids
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► Advantages: Easy to process
► Disadvantages Fixed resolution leads to redundancy or inadequacy
Regular Grids ..Regular Grids ..
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► A series of elevation points along individual contour lines
2. (2) Contours2. (2) Contours
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► Elevation values along a series of parallel lines
2. (3) Profiles2. (3) Profiles
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► Triangulated Irregular Network► It is a network of triangular facets► For each vertex, the x, y, and z value are recorded► The nodes and edges follow the important terrain features such as ridges, stream lines, high points, passes, and so on.
2. (4) TINs2. (4) TINs
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TINs ..TINs ..
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TINs ..TINs ..
X=3970Y=3869Z=7746
X=4562Y=4219Z=7906
X=4266Y=4044Z=7826
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SlopeSlopeTIN
Grid
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TINs ..TINs ..
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► TIN topology X and y coordinate table: node ID, x and y Z coordinate table: node ID, z value
Node table: triangle ID, node IDs Edge table: triangle ID, edge IDs
TINs ..TINs ..
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TINs ..TINs ..
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► Advantages efficient in storage accurate encoding for the break-point features
► Disadvantages difficult to implement
TINs ..TINs ..
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► Existing contour map► Stereoscopic aerial photography► Stereoscopic satellite images► Ortho-photos and Ortho-images - Aerial photo or image that has been corrected for all motion, attitude, and viewing perspective as well as relief displacement
3. Source Data of DEM3. Source Data of DEM
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► USGS, state agencies, and private vendors
► 1:24,000 DEM► 1:250,000 DEM
4. Data Availability4. Data Availability
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► Developed and distributed by USGS► A regular grid in UTM coordinate system► A 7.5 by 7.5 minute coverage
4. (1) 1:24,000 DEM4. (1) 1:24,000 DEM
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► Data are ordered from south to north in profiles that are ordered from west to east
► A 30 by 30 meter spacing along and between profiles (spatial resolution)
► The profiles do not always have the same number of elevation points
► The measuring unit for the elevation is meter in most cases
1:24,000 DEM ..1:24,000 DEM ..
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► The profiles do not always have the same number of elevation points
1:24,000 DEM ..1:24,000 DEM ..
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► Developed by Defense Mapping Agency and distributed by USGS► A regular grid in geographical coordinate system► A 10 x 10 coverage► The measuring unit for the elevation is meter► The spacing along profiles is 3 arc-second (“spatial resolution”)► The spacing between profiles is arc-second below 500N latitude, 6-9 arc-second otherwise
4. (2) 1:250,000 DEM4. (2) 1:250,000 DEM
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► A 10 x 10 coverage► The spacing between and along profiles is 3 arc-second
4. (2) 1:250,000 DEM4. (2) 1:250,000 DEM
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► Volume estimation► Contour map► 3D display► Visibility► Slope, convexity, concavity, aspect► Watershed delineation/stream lines
5. Applications of DEM5. Applications of DEM
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Volume Volume EstimatioEstimatio
nn
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ContoursContours
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Contours and 3DContours and 3D
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NIMA &NASANIMA &NASA
3D3D
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3D3D
A. Toy, SUNY BUffalo
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3D display3D display
Bowling Green
Z=10
J. Yan, SUNY BuffaloJ. Yan, SUNY Buffalo
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3D display3D display
J. Yan, SUNY BuffaloJ. Yan, SUNY Buffalo
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VisibilityVisibilityLine of sight
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VisibilityVisibility
The above maps show the results of analyses around Saddleback (left) and Old Blue (right) mountains. On the maps, green areas are visible from the location cited (shown in yellow), while gray areas are obstructed from view. The Appalachian Trail is shown in red.http://www.northgeo.com/services/carto/projects/LURCViewshed.htm
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VisibilityVisibility►3 scenic 3 scenic lookoutslookouts
M. Dolce, Buffalo State CollegeM. Dolce, Buffalo State College
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Cave modelingCave modeling
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ElevationElevation
NIMA & NASANIMA & NASA
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Slope Slope aspectaspect
Derived Derived from DEMfrom DEM
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Slope Slope angleangle
Derived Derived from DEMfrom DEM
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Stream FunctionStream Function
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Color infrared composite of the IKONOS Color infrared composite of the IKONOS draped over the DEM as viewed from the west draped over the DEM as viewed from the west
side of the study area to the east from an side of the study area to the east from an elevation of 10,000 m, Xichang, Chinaelevation of 10,000 m, Xichang, China
Xu, University of Utah, Gong, UC-BerkeleyXu, University of Utah, Gong, UC-Berkeley
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ReadingsReadings
Chapter 3