[GRASSLIST:3078] Re: USGS DEM's

[Roger Miller]

On Sunday 03 February 2002 14:08, sbt wrote:

> I understand grass can import USGS 1:250K or 1:24K DEM data
> (downloadable at
> http://edcwww.cr.usgs.gov/doc/edchome/ndcdb/ndcdb.html), but I don't
> know how.  Anyone care to lead a newbie by the hand?

These are both provided in sdts format.  At least for the 1:24K DEM data the 
edcwww site will refer you to a commercial site (gisdatadepot, if I remember 
correctly) where the normal download speeds are glacial.  Download them 
directly from edc if you can.

I can't walk you through all the details, but here's basically what you do:

Download the file as a tarred archive and unpack the file.  I unpack the 
files in an empty directory.  The unpacked tar file will produce a large 
number of smaller files. Find the file with the named <something>CATD.DDF.

Start GRASS and make sure that your current location is correct for the map 
you are downloading.  The projection and coordinate system should match the 
projecton and coordinate system used for the map.  The limits of your current 
region should include the area of the map.

Use r. in.gdal to perform the input.  You will need to supply the 
<something>CATD.DDF file as the input file to r.in.gdal.  You will also need 
to provide an output file name.  The output file will be created in your 
current mapset.  You can also just let r.in.gdal create a new location 
appropriate for the map.  Read the man page for r.in.gdal for more details.


Roger Miller