[GRASSLIST:5257] Re: USGSDEM export

[Dylan Beaudette]

On Tuesday 28 December 2004 01:18 am, Roger Bivand wrote:

----snip snip---------

> > > So my guess is that if you really need USGSDEM
> > > output you could probably
> > > do it by outputting to GeoTIFF and then using
> > > gdal_translate (not a
> > > GRASS tool, it comes with the gdal library):
> > >
> > >   gdal_translate -of USGSDEM intermediate.tiff
> > > Final.DEM
> > >
> > > HTH,
> > > T.
> >
> > Thanks Tom,
> >
> > My only scruple is GeoTIFF would destroy the
> > information. Could that be true?
>
> My reading of:
>
> http://www.gdal.org/frmt_gtiff.html
>
> suggests that you should be OK, the range of band types is pretty large,
> and less problematic than USGSDEM:
>
> http://www.gdal.org/frmt_usgsdem.html
>
> Roger
>
> > Miha Staut

I have noticed this as well in trying to reproject a NAD27 DEM to a NAD83 DEM 
via gdalwarp. I found that the datum conversion worked fine if I first 
created an intermediate GTiff as Richard suggested. Since i was only 
interested in getting the data into GRASS, the intermediate geotiff was 
enough. 

However, I had to manually set the USGS NODATA value left over from the DEM to 
NULL in GRASS. I used r.mapcalc, but I imagine that r.null would work even 
better.

Cheers,

-- 
Dylan Beaudette
Soils and Biogeochemistry Graduate Group
University of California at Davis
530.754.7341