Reading an SDTS DEM from the USGS or Northridge:
- Download your SDTS file from the USGS or CSU Northridge. I'll assume you're saving
it to your zip disk (G:) and you're working in a folder called "myworkspace".
- The filename indicates the cell size and quality (level) of the data. The first
number is probably either "30" or "10" and indicates the cell size.
After a dot is the level: level 1 is the lower quality DEM created by the Gestalt
Photomapper; level 2 is generated from scanned contours. If you have a choice, go
with level 2. So, "30.1." means 30 meter grid, level 1, "10.2."
means 10-meter grid, level 2, etc.
- The file should end with ".tar.gz". If there isn't a dot in front of the
"tar" (sometimes the browser will replace "." with "_"), you
should edit the file name to include it. You might want to save it with the name of
the quad, but finish it with ".tar.gz".
- Unzip the zipped file by double-clicking it, and letting winzip uncompress it to a
folder. Extract all the files into a folder you can name something obvious like
"virginriver". All of the files end in .ddf and all start with a
consistent 4-character code -- write it down. For this dataset it's
"ttt3".
- Say you're working in "myworkspace" on g:, start Arc, and set your workspace
to that folder with
"w g:\myworkspace". For the next step, I'm assuming that your
"virginriver" folder is within "myworkspace".
- Convert the SDTS to an elevation grid called "virginelev" with the Arc
command:
"sdtsimport virginriver\ttt3 virginelev"