Convert GTOPO30 DEM data into a grid using ArcINFO GRID

Summary

Instructions provided describe how to convert GTOPO30 DEM data into a grid. Use ArcInfo GRID to convert a USGS GTOPO30 DEM to grid format while retaining the digital elevation data values.

Click the link in the Related Information section to 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.

Procedure

1. Uncompress the .TAR file using WinZip 6.2 or higher.
2. Change the *.dem extension to *.bil.
3. Use IMAGEGRID at the Arc prompt to convert the *.bil to a grid.
4. Use the CON statement in GRID:
   
   

   Code:
   out_grid = CON(in_grid >= 32768,in_grid - 65536,in_grid)  

   
   
5. Convert the ocean areas (-9999), if desired, to NODATA using SETNULL:
   
   

   Code:
   out_grid2 = SETNULL(out_grid == -9999,out_grid)