comparison of data

[Lars Schylberg]

There is many ways to do this, but my favorite program r.mapcalc could be 
a good start.

echo "diff.map=if( map1 != map2)" | r.mapcalc

Then you could examine what values that have changed with r.stats
and count numbers of pixels at the same time.

r.stats -c input=diff.map,map1,map2

Lars

Lars Schylberg                          Email: larss at fmi.kth.se  
Dept. of Geodesy and Photogrammetry 
Royal Institute of Technology (KTH)     Tel.   +46 8 790 86 33   
S-100 44  STOCKHOLM, SWEDEN             Fax.   +46 8 790 66 10

> Hi
> I,m a new user of GRASS,and I'd like to be able to compare maps (with
> the same categorie values).Does anybody know how to do it?
> I've got map of vegetation with ,for example 5 or 10 classes,and
> I'd like to get the DIFFERENCE between those maps.It 's look
> easy to combine or overlay map in Grass,but I just can't find
> useful commands to make comparison...