I've downloaded several 7.5 minute DEM files from USGS and they have file names like:


On MAC these decompress into a folder with serval files having the extension '.DDF'. Is there a shareware program that allows me to convert them to a basic ASCII text DEM file under the Mac OS X operating system?


GDAL is a free geospatial raster translation program that will convert USGS sdts dem to USGS asci dem. A Mac installer is available here gdal installers.

I'm unfamiliar with a Mac, but you will run gdal_translate.exe from a command line. Something like gdal_translate -of USGSDEM 1661629.DEM.SDTS. -of is the output format. The gdal_translate command help page is here translate These are gdal format abbreviations formats

  • thanks. I've downloaded but dont see a new Application. What exactly am I running! – Robert Sep 4 '13 at 20:55
  • I found the gdal_translate.exe which is installed under the /Library/Frameworks/ directory. After creating the ~/.bash_profile and adding the code below it runs from any directory:export PATH=/Library/Frameworks/GDAL.framework/Programs:$PATH I've managed to run the translator using Mac Terminal: gdal_translate -of USGSDEM 1663331.DEM.SDTS.TAR.GZ 1663331.DEM However, i get the error message below: ERROR 4: 1663331.DEM.SDTS.TAR.GZ' not recognised as a supported file format. Am I wrong in thinking it will read the compressed file? What should it be? – Robert Sep 5 '13 at 3:38
  • @robertprince-wright - Either uncompress or use the special GDAL "/vsitar" virtual filesystem syntax, i.e. gdal_translate -of USGSDEM /vsitar/1663331.DEM.SDTS.TAR.GZ 1663331.DEM – user2856 Sep 5 '13 at 4:54
  • @Luke - thanks, I've uncompressed the files and you end up with about 20 files with the DDL extension. I tried running 'gdal_translate' using the folder name but that fails too. So is there a specific file I need to point to? – Robert Sep 5 '13 at 13:21
  • My problem is solved by uncompressing the file and then pointing to the file containing 'CATD'. I presume it has special pointers to the other files. – Robert Sep 5 '13 at 17:49

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