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11.G.vii. Importing into ERDAS

Users of ERDAS may import the DEM files (GUNZIP decompressed) using the following procedure. Importing the northwestern (file a10g) tile of GLOBE into ERDAS is presented as an example.

  • Start ERDAS. Click on the Import button. In the Import/Export template that appears, select Generic Binary for Type and the appropriate response for Media. Enter a10g as the input filename. The default output filename is a10g.img. Click OK and Close.
  • The Import Generic Binary Data template is displayed next. Enter 10800 for the number of columns and 4800 for the number of rows. (The number of columns is always 10800. The number of rows is 4800 for tiles that cover 50o-90oN or 50o-90oS latitude and 6000 for tiles that cover 0o-50oN or 0o-50oS latitude.) For Data Type use Unsigned 8 bit if importing a source/lineage file, and Signed 16 bit if importing a GLOBE DEM file. The data format type is BIL. If you are running UNIX ERDAS, click on Swap Bytes and click OK to begin the import. When the import is complete, click OK again. Close the Import/Export template window.
  • Select Image Information from the Tools pulldown menu. The ImageInfo template is then displayed. Click Open from the File pulldown menu and select a10g.img and click OK. Select Change Map Model from the Edit pulldown menu. Enter the appropriate x (longitude) and y (latitude) coordinates for the imported data set; for tile a10g the x coordinate is -180 and the y coordinate is 90. This information is found in Table 3 (Section 11.C). Next, enter 0.00833333 for x and y pixel sizes. Set the Projection to Geographic (lat/lon). The Units should automatically change to Degrees. Click OK. When a confirmation window pops up, click OK again. Leave the ImageInfo window open.
  • In the ImageInfo template, select Compute Statistics from the Edit pulldown menu. The Statistics Generation Option template is then displayed. Change the Skip Factor to 1 and the Skip Factor Y to 1. Change the Bin Function to Linear. Then click OK. After the statistics are computed, confirm that the information in the ImageInfo window is correct and close the window.

Your data should now be in ERDAS, in latitude/longitude projection. The file can be displayed as a raster layer. Some ERDAS processes (such as computing shaded relief images) may want you to reproject the data, or at least signify to ERDAS that the data are in a projection other than Geographic.

ERDAS adds header and footer information to GLOBE's binary raster grids as part of the procedure described above for importing new files. Earlier versions of ERDAS performed this task with the functions FIXHEAD and BSTATS. FIXHEAD details the numbers of columns and rows, georeferencing, number of bytes, etc. This information is provided in Table 3 (Section 11.C). BSTATS is run after FIXHEAD, appending statistical information to the end of the file.


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