[Qgis-user] Re: how to subtract or add one raster layer to another

[Dr. F. Patrick Graz]

I think I'm a bit late on the scene in responding to this query.

If you are going to use a current (1.5) installation - see if you have GRASS
installed (an option during installation). If you do then have a look at the
r.mapcalc functionality. Mind you, if you have not used GRASS very much it's
a bit of a learning curve - I think that time investment is worth it, but
then, I'm biased :-)

Patrick

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Dr. F. Patrick Graz
Snr. Researcher, 
Multidisciplinary Research Centre, 
University of Namibia