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[Susan Stitt]

>Date: Tue, 23 Nov 93 11:49:18 PST
>From: khanna at alnitak.usc.edu (Gurcharan Khanna)
>To: grassu-list at max.cecer.army.mil
Subject: extracting DEM data

>hi,

>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

You are confusing DEM data with "DMA" data.  Yes USGS is now
calling them all DEM data, but the 1:250000 scale digital
elevation files used to be referred to as "DMA" data or 
Defense Mapping Data.  These files are 1 degree by 1 degree
and were originally created by the Defense Mapping Agency.
They have been reprocessed and are available from USGS.  
This has become a confusing problem for folks.

You need to use the m.dma.USGSread utility.  

Yes there is a tutorial:

DTED and DEM Elevation Data Extraction 
by Stuart Bradshaw, Mary Martin, Chester Kos, and Scott Tweddale

I'm sure it is available from the moon.

Good Luck!

Susan Stitt   National Biological Survey   sstitt at nps.gov