> 
> Is there a simple program available that will allow me to determine the 
> average value for a raster data set. 
> 

The r.le tools, by Bill Baker, will do the calculation for you very
simply and quickly (though they are not simple tools).  You can
use the command
  r.le.pixel map=map.to.be.averaged att=b1,b2,b3,b4
to get mean, standard deviation, minimum and maximum cell values,
for the whole map.  If you have another raster map of polygons that
you want to use as categories over which to calculate the statistics,
then use
  r.le.pixel map=map.to.be.averaged sam=r reg=categories.map att=b1,b2,b3,b4

If your site hasn't compiled the r.le tools, you can get them from
the moon.cecer.army.mil ftp site, in the /grass/incoming directory.
The files are called rle21*.

Tim.

 -----------------------------------------------------------------
 Tim Martin                     *  
 Spatial Information Systems    *     If you want peace,
 University of Alberta          *     prepare for justice.
 martin@ulysses.sis.ualberta.ca * 
 -----------------------------------------------------------------


