extracting DEM data

Gurcharan Khanna khanna at alnitak.usc.edu
Tue Nov 23 14:49:18 EST 1993


i have recently installed Grass4.1 on a SunSparc server and have
started setting up some data layers for los angeles. i have imported
Tiger files with no problem. But now i can't seem to import DEM files
with any success.

1) is there a tutorial for m.dem.extract or other ways to import DEM files?

2) otherwise, here is what i am trying:
	a) obtained DEM files from usgs ftp site.
	b) start grass set to my LA database
	c) use g.region to set region to something slightly larger than
	   the header info from the DEM indicates
		set res to 00:00:03
	b) using m.dem.extract to extract data
	   setting start and end file number = 1
	c) data extraction completes successfully with 1201 rowsxcols
	d) d.erase; d.rast shows only single color for entire display

am i missing some step? i even tried changing the color table with r.colors,
and running r.support explicitly, but with no change.  i can display my
Tiger data maps without any problems. any help would be appreciated.

thanks very much,

 gurcharan s khanna
 university computing services/
 dept. of geography
 univ. of southern california

 this is the txt file accompanying the DEM file:

Raw Digital Elevation Model Data Holdings, DSDL - Reston
    *File Name: los_angeles_w    DEM Level: 1
    *Source Date: XX/19XX   Process:
    *Inspected or revised: NO   Date: NONE
    *Mapping Center:
    *Number of rows: 1201  Number of columns: 1201
    *Minimum Z value: 0.0   Maximum Z value: 2682.0
    *Resolution  X: 3.0  Y: 3.0  Z: 1.0
    *Coordinate System: GEOGRAPHIC     Units: ARC-SECONDS
    *Vertical datum: NGVD29  Horizontal datum: WGS72
    *Minimum_latitude: 34
    *Minimum_longitude: -120
    *Maximum_latitude: 35
    *Maximum_longitude: -119

More information about the grass-user mailing list