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Geographic Information Systems

Geographic Information Systems. Digital Elevation Models (DEM). 1. Digital Elevation Model. A set of elevation measurements for locations distributed over the land surface. 2. Basic Methods to Capture and Store DEM Data. Regular grids Contours Profiles

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Geographic Information Systems

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  1. Geographic Information Systems Digital Elevation Models (DEM)

  2. 1. Digital Elevation Model A set of elevation measurements for locations distributed over the land surface

  3. 2. Basic Methods to Capture and Store DEM Data Regular grids Contours Profiles Triangulated irregular network (TIN)   

  4. 2. (1) Regular Grids 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

  5. Regular Grids .. Advantages:   Easy to process Disadvantages   Fixed resolution leads to redundancy or inadequacy

  6. 2. (2) Contours  A series of elevation points along individual contour lines

  7. 2. (3) Profiles Elevation values along a series of parallel lines

  8. 2. (4) TINs 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.

  9. TINs ..

  10. X=3970 Y=3869 Z=7746 X=4266 Y=4044 Z=7826 X=4562 Y=4219 Z=7906 TINs ..

  11. Slope TIN Grid

  12. TINs ..

  13. TINs .. 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

  14. TINs ..

  15. TINs .. Advantages   efficient in storage      accurate encoding for the break-point features Disadvantages    difficult to implement

  16. 3. Source Data of DEM 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

  17. 4. Data Availability USGS, state agencies, and private vendors 1:24,000 DEM 1:250,000 DEM

  18. 4. (1) 1:24,000 DEM Developed and distributed by USGS A regular grid in UTM coordinate system   A 7.5 by 7.5 minute coverage

  19. 1:24,000 DEM ..  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

  20. 1:24,000 DEM ..  The profiles do not always have the same number of elevation points

  21. 4. (2) 1:250,000 DEM  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 ismeter 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

  22. 4. (2) 1:250,000 DEM A 10 x 10 coverage  The spacing between and along profiles is 3 arc-second

  23. 5. Applications of DEM Volume estimation  Contour map  3D display  Visibility  Slope, convexity, concavity, aspect  Watershed delineation/stream lines

  24. Volume Estimation

  25. Contours

  26. Contours and 3D

  27. 3D NIMA &NASA

  28. 3D A. Toy, SUNY BUffalo

  29. Bowling Green 3D display Z=10 J. Yan, SUNY Buffalo

  30. 3D display J. Yan, SUNY Buffalo

  31. Line of sight Visibility

  32. Visibility 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

  33. Visibility • 3 scenic lookouts M. Dolce, Buffalo State College

  34. Cave modeling Fisher, Erich , 2005. 3D GIS archaeology in South Africa: archeologists workingalong the South African southern coast use multidimensional GIS applications tomodel Pleistocene caves and paleo-environments reconstructing the landscape CA.420,000 to 30,000 BP. GEO:connexion, 4 (5): 40

  35. Elevation NIMA & NASA

  36. Slope aspect Derived from DEM

  37. Slope angle Derived from DEM

  38. Stream Function

  39. Color infrared composite of the IKONOS draped over the DEM as viewed from the west side of the study area to the east from an elevation of 10,000 m, Xichang, ChinaXu, University of Utah, Gong, UC-Berkeley

  40. Readings Chapter 3

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