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Dan Scholes

Map Projection for ENVI Users

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Note for ENVI users of map-projected data: Some Geosciences Node hosted map-projected data sets (.IMG files) are not read by ENVI as projected data sets. Using the Geospatial Data Abstraction Library (GDAL) gdal_translate command, users can easily convert most of these data products into GeoTIFF or ENVI file formats which are read by ENVI as projected data.

GDAL packages for various computer systems can be found here: https://trac.osgeo.org/gdal/wiki/DownloadingGdalBinaries. The Windows package used in this example is the OSGEO4W 64-bit version. A MacOS X build is available, as well.

  • Download and install a GDAL package that has gdal_translate.exe.
  • gdal_translate.exe runs from the command line. Make the folder that contains gdal_translate.exe your current directory
    • To do this, type "cd path" without the quotes into the command line, where "path" is the full path to the folder that contains gdal_translate.exe.
  • gdal_translate.exe is executed with the following syntax:
    • gdal_translate –of outputtype inputfilepath outputfilepath
    • "outputtype" is GTiff for a GeoTiff (.tif) and ENVI for an ENVI file (.dat)
    • Both file paths are the full path to the file.
    • In the case of a file with a detached PDS label, the "inputfilepath" points to the label, not the data file.
  • Open the file as normal in ENVI.

Example using OSGeo4W 64-bit (Windows):

C:\>cd OSGeo4W64\bin

C:\OSGeo4W64\bin>gdal_translate -of GTiff C:\hrsc\h2064_0000_dt4.img C:\hrsc\h2064_0000_dt4.tif

Example using GDAL 2.1 Complete (MacOS X):

:/ cd Library/Frameworks/GDAL.framework/Programs
:Programs ./gdal_translate -of ENVI /Desktop/hrsc/h2064_0000_dt4.img /Desktop/hrsc/h2064_0000_dt4.dat

Examples of data sets that benefit from the GDAL translate command:

  • MRO - HiRISE DTM
  • Mars Express - all HRSC, OMEGA DDRGM
  • Odyssey - THEMIS IRGEO2, VGEO1, VGEO2
  • MGS - MOLA MEGDR, TES TIMAP

Additional instructions for specific data sets:

  • Mars Odyssey THEMIS Visible map-projected .CUB files (VGEO1 and VGEO2) have detached PDS labels, but the map-projection data is in the .CUB file, so the "inputfilepath" should be the data file itself.
  • Mars Odyssey THEMIS Infrared map-projected .CUB.gz files (IRGEO2) need to be un-zipped before using gdal_translate. These data are similar to the visible data files in "inputfilepath" syntax (.CUB, not .LBL).

More details about the gdal_translate command can be found at http://www.gdal.org/gdal_translate.html.

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