[GRASSLIST:2950] Re: numerically compare 2 rasters

Massimiliano Cannata massimiliano.cannata at supsi.ch
Mon Mar 15 06:15:34 EST 2004

What about create a difference raster?
you can do with
    r.mapcalc diff=rast1-rast2
So you can see in a moment where difference are.....

dylan wrote:

>i have 2 raster images that i would like to compare numerically. for the
>time being, a simple linear regression would suffice.
>these rasters are basically 84 selected points from a much larger raster
>image - therefore there should only be 84 pixels that are not NODATA.
>i have tried dumping the rasters as ascii, removing the NODATA values, and
>setting up a table as follows:
>raster1_values | raster2_values
>v1             | v1
>v2             | v2
>...            | ...
>however, when i plot the values i am getting very unusual results. it could
>be that my plots are valid, but could i be doing something strange here?
>thanks in advance,

note: change my e-mail reference to massimiliano.cannata at supsi.ch
      because the old one will be deleted soon.
Ing.  Massimiliano Cannata
Istituto di Scienze della Terra - SUPSI
C.P. 72 - CH-6952 Canobbio (Ticino, Switzerland)
Tel +41 91 /935 12 25 - Fax +41 91 /935 12 09
eMail: massimiliano.cannata at supsi.ch
Internet: http://www.ist.supsi.ch

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