Thursday, July 22, 2010

Create Slope or Slope directions ESRI ArcGrid ASCII files with Global Mapper

Global Mapper can be used to generate terrain slope values or slope directions (aspect) grid files in ESRI ArcGrid ASCII formats from surface elevation data. This is a two part conversion process workflow instead of a straight export from surface elevation data. The conversion to slope values or directions involves: (1) conversion from elevation to slope values/directions in float/grid file format, and (2) conversion from float/grid format to ESRI ArcGrid ASCII format.

Conversion from elevation to slope values/directions in float/grid format
  1. Start up Global Mapper and load up a surface elevation dataset.
  2. Select File | Export Raster and Elevation Data | Export Float/Grid File.

    The Float/Grid Export Options dialog box appears.









  3. Optional: type in the desired sample spacing values and units.
  4. Toggle on Export Slope Values instead of Elevations to export slope values.
    Or toggle on Export Slope Direction Values Instead of Elevations to export slope directions.










  5. Click OK.

    The Save As dialog box appears.









  6. Type in the output file name e.g. slope.flt. Click Save.

    The elevation data is exported out as slope values or slope directions into the output file.
  7. Close Global Mapper.
Conversion from float/grid format to ESRI ASCII ArcGrid
  1. Start up a Global Mapper and load the slope values/directions float/grid file generated in the previous section.




  2.  Select File | Export Raster and Elevation Data | Export Arc ASCII Grid.

    The Arc ASCII Grid Export Options dialog box appears.




  3. Optional: type in the sample spacing values and choose a vertical unit.  Click OK.

    The Save As dialog box appears.
  4. Type in the output file name, e.g. slope.asc. Click Save.

    The slope values/directions ESRI ASCII ArcGrid file is created

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