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Converting compressed SDTS
files into USGS DEMs
Most of the 7.5-minute USGS DEM
files are in the SDTS (Spatial Data Transfer Standard) format.
You'll have to do a few things to the files before you can import
them in WCS.
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1.0. Extract 18 SDTS modules
(files) and README from the tar.gz file. Step 1.1 explains
extraction using Windows NT-based programs. Step 1.2 uses gunzip and tar
for Windows NT DOS. If you already have the 18 DDF files pass
go and proceed with Step 2.
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1.1. Using a Windows NT based
decompression utility (WinZip 6.3 and WinPack32 2.3 tested) to
unzip and untar the TAR.GZ file.
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1.1.1. Decompress the TAR.GZ
file. If the unzipper doesn't recognize the file as a tar file
a window will pop up asking you to rename it. If this happens,
try renaming the unzipped file with a .TAR extension. |
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1.1.2. If all goes well the extracted
.TAR file should give you 18 DDF modules, a readme, and
a UCOMMENT text file. |
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1.2. Using GUNZIP and
TAR for Windows NT DOS.
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1.2.2. Rename the tar.gz
to something short .gz to make it easier to type. |
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1.2.3. Run the following from
the NT DOS window to gunzip the file:
gunzip filename.gz |
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1.2.4. Gunzip will make a
new file called filename_tar (no extension). |
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1.2.5. Run the following from
the NT DOS window to untar the file:
tar -xvf filename_tar |
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1.2.6. This will (should) give you
18 DDF files, a readme, and a UCOMMENT text file. |
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2.0. Convert the SDTS modules
into a USGS DEM that WCS recognizes.
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2.1. Unzip the sdts2dem
converter beta 10. There may be a more recent release at
ftp://ftp.blm.gov:21/pub/gis/sdts/dem
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2.2. Copy the sdts2dem.exe
file to the temporary directory with the .ddf files. |
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2.3. Run the following from the
NT DOS window to convert the file:
sdts2dem xxxx
newname l0
where xxxx are the first
4 numbers of the .ddf files you're converting, newname
is the new filename you want with no extension, and l0
(that's lowercase L zero) are the 7th and 8th characters
of the xxxxcel0.ddf file. If you don't have an xxxxcel0.ddf
then this isn't a DEM file and the conversion won't work. The
conversion program should run like this if you've done everything
right. |
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3.0. Import the DEM file into WCS
using the Data / Extract USGS DEM window. |
STDS FAQ page
http://mcmcweb.er.usgs.gov/sdts/sdtsfaq.html#sub4.2.1
"Everything You Wanted To
Know About SDTS But ..." 72-page PDF
ftp://sdts.er.usgs.gov/pub/sdts/datasets/raster/dem/demmap.pdf
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