[GRASSLIST:2181] Importing a USGS ASCII DEM

GRASS GRASS user
1

Hi,

I've imported a USGS ASCII DEM using r.in.gdal, but when I use d.rast
to display it, it is all red. I've tried changing the color table,
but to no avail. Using d.what.rast show different values at different
places, so I'm not sure why they won't show up in different colors.
This particular dem file has extension ".dem". I have successfully
imported another USGS ASCII DEM which has extension ".cdo". Not sure
what the difference is...gdalinfo shows them both to be DEMs.

Here's the data in question:
ftp://gisweb1.radford.edu/dem/county_dem/carroll_dem.zip

Any ideas?

Thanks,
Ben

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2

Ben Logan wrote:

I've imported a USGS ASCII DEM using r.in.gdal, but when I use d.rast
to display it, it is all red. I've tried changing the color table,
but to no avail. Using d.what.rast show different values at different
places, so I'm not sure why they won't show up in different colors.

Check the range (r.info) of the data, and optionally the distribution
(e.g. with d.histogram).

A common problem when importing DEMs is that a specific (and usually
extreme) value is often used to represent NULLs. If these aren't
converted, the result is that the colour table gets stretched over an
extreme range, with the "real" data lying in a narrow band (relative
to the overall range).

If this has happened, you can translate the substitute NULL values to
actual NULLs with r.null.

--
Glynn Clements <glynn.clements@virgin.net>