Importing GTOPO30 into ArcView

 

From ESRI website, article 14707:

 

Download a GTOPO30 DEM. This file comes as a .TAR file, which contains the *.dem and *.hdr files. Both files are required for this operation.

  1. Uncompress the TAR file using WinZip 6.2 or higher. Make sure that under Option>Configuration>Miscellaneous the 'TAR file smart conversion' is NOT ticked
  2. Change the file extension from *.dem to *.BIL. You can do this from Windows Explorer or a Command Prompt window.
  3. In ArcView, add the *.BIL to a view as an image theme.
  4. Make your Spatial Analyst extension active, if it was not already
  5. Make the BIL image the active theme in the view.
  6. Select Convert to GRID from the Theme menu.
  7. Specify a name and directory location for the new grid on the Convert dialog box.
  8. Click OK.
  9. Select Yes when asked to add the grid to the view.
  10. Make the new grid the active theme in the view.
  11. Select Map Calculator from the Analysis menu.
  12. Enter the following equation into the expression box on the Map Calculation dialog.

([in_grid] >= 32768).con([in_grid] - 65536, [in_grid])

Note: in_grid is the grid created in steps 4-6, so replace with your file name if needed

  1. Click Evaluate and close the Map Calculation dialog.
  2. Make the new Map Calculation Theme the active theme.
  3. Select Map Calculator from the Analysis menu.
  4. Enter the following equation in the expression box on the Map Calculation dialog.

([Map Calculation 1] = -9999).setnull([Map Calculation 1])

Note: Map Calculation 1 is the grid created in step 12.

  1. Click Evaluate and close the Map Calculation dialog.
  2. Your new grids have to be saved, as you will lose them if you do not save your project, and even if you do, the grids will be in your temp folder with a temporary name. There are two options 1) Theme>Save Dataset or 2) File>Manage Data sources>Copy Grid. Create a directory first for grids only, and make sure you know which grid you need to save (See Theme>Properties for file name and location). Add your new grid to test if it works, then delete the temporary grids using the same Data Source manager.

Notes:    - The first formula is a conditional form of calculation, needed on PCs to set the byte order

properly (Intel rather than Motorola). For any values higher than 32768, 65536 will be

subtracted.

- The second one has to do with ocean values being -9999 in GTOPO30 data, which have to be set to 0.

 

See http://www.esri.com/news/arcuser/0101/avfiles/lesson10.pdf for hardcopy.

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