DEM Extraction: How to?

[Michael Hanratty]

In message <9706021714.AA20042 at ouray.cudenver.edu>  writes:
> Dear Grass Users,
>
<snip> 
>Therefore, does anyone have a suggestion as to
> where to look for a step by step procedure for extracting 1:250,000-Scale
> Digital Elevation Model (DEM) data provided by USGS into GRASS 4.1 (if such
> a document exist!) ?
> 
> 
I don't know where to find it, but here's my notes on how I do it:

To convert USGS dem files to GRASS format:

1. convert ascii file to binary:
m.dmaUSGSread top=1 bottom=1201 left=1 right=1201 output=binfname
        logfile=logfname < demfname

2. Rotate binary file 90 degrees, creating dem in lat-long format
m.rot90 [-q] input=binfname output=llfname rows=1201 cols=1201
     bpc=2

3. Convert from lat-long to UTM projection and put in GRASS database
 r.in.ll [-s] input=llfname output=rastfname bpc=2
        corner=corner,lat,lon dimension=1201,1201
        res=3,3 spheroid=wgs72
    The latitude and longitude of the sw corner is the first pair of
the 6-digit values in the header of the original dem file.  These six
digit values are arc-seconds.  Divide by 3600 to get degrees. Enter
these values in the corner= input value for r.in.ll.


Hope this helps.


Michael Hanratty                           Phone: (612) 627-4590
St. Anthony Falls Laboratory               Fax: (612) 627-4609
Dept. of Civil Engineering
University of Minnesota
Mississippi River @ 3rd Ave. SE
Minneapolis, MN 55414