<—DTM MAIN PAGE

How to Use Digital Terrain Models (DTMs)

The HiRISE DTM is a 32-bit .IMG format. It is not a disk image file. The .IMG is a PDS standard raster file format.

ArcGIS 10 will open the .IMG file directly, but the nodata value needs to be set manually using the Data Management > Raster toolbox. ArcScene and ArcGlobe may also work, but the resolution takes a hit. See the Planetary GIS support pages for more info.

GDAL (gdal_translate) will convert the .IMG into a geotiff, which may be opened by more types of software. ArcGIS 9.x will read the geotiff created this way. The caveat here is that different versions of GDAL read the mapping keywords in the label differently. See attached gdal_usage_notes.txt for more information about installing and using GDAL.

ENVI and Matlab can also open the files. The ENVI HiRISE Toolkit will read all HiRISE RDR products, including JP2s and the DTM IMG files.

In ISIS 3, the .IMG file can be converted into a cube using pds2isis. JP2 support might be available in ISIS now, but you will probably need to convert our JP2s to ISIS cube format in a two-step process. First run JP2_to_PDS (available here ), then the ISIS program pds2isis. This approach is more for the scientist looking to do analysis on the DTM and orthoimages.

There are other ways of opening HiRISE DTMs for visualization, such as Blender, which is free and has a HiRISE plugin available. The plugin is already included in the public release of Blender since version 2.5.7. Here are some Blender instructions to get you started:

1)Turn on the plugin by going to File > Users Preferences > Import/Export. Check the box that says Import/Export: HiRISE DTM from PDS IMG.

2) Click the Save As Default button and close the Preferences pane.

3) In Blender, under File, select Import > HiRISE DTM from PDS IMG (*.IMG).

4) Navigate to the directory where you saved the DTM. Click ONCE on it to select it. Then choose the import option in the left panel that sets the import compression. The options are 2x2 (really slow, not recommended), 6x6, 6x6 fast, 12x12 and 12x12 fast. For the first time, the 12x12 fast is recommended. It may still take a few minutes depending on the power of your computer.

5) You can “drape” any of the browse jpeg images over the DTM (except in some of the polar DTMs, where the scaling might be off), such as the colorized altimetry ..ca.jpg. This is done by setting the material property to be one of those images.