Hello Clifford,

I believe your problem is that USGS DEM data is not in dma format, rather
it is in dted format.  Try the following on your uncompressed data file at
the grass prompt:

grass4.1>dd if=aztec-w ibs=512 | m.dmaUSGSread top=1 bottom=1201 left=1
right=1201 output=aztec-wd logfile=aztec-wd.log

Then rotate the file:

grass4.1>m.rot90 input=aztec-wd output=aztec-wd.rot rows=1201 cols=1201
bpc=2

Produce a grass raster (cell) file of elevation data:

grass4.1>r.in.11 input=aztec-wd.rot output=aztec-w.dted bpc=2
corner=se,36N,107W dimension=1201,1201 res=3,3 spheroid=wgs72

In the above example, I was working with 1:250,000 DEM from the USGS, and 
the half quad (west) was named aztec.  The corner location and resolution
will be different and the dimensions of the data for 1:24,000 quad might
be different.  The selection of spheroid is based on the desired final
projection.


I hope this helps.

> I have been trying to extract a USGS 1:24K DEM using m.dem.extract.  
> 
> for all of the files in this DEM dataset.  There supposedly exists 1 C-type
> record.  Is my problem from using m.dem.extract on a disk file rather than
> a tape?
> 

==========================================================================
Louis Clarke, biologist               U.S. Army Corps of Engineers
lclarke@alb-co-r.swa.usace.army.mil   Albuquerque District
(505) 766-2776


