[GRASS-user] calculating statistics based upon a raster patch map

[Martin Wegmann]

On Donnerstag, 20. November 2008 13:57:42 Hufkens Koen wrote:
> Hi list,
>
> I've got two maps, a map with patches or areas which I want to evaluate. A
> second map contains a parameter which I want to evaluate (average, std)
> based upon areas as delineated in the first map. The output of all this
> would optimally be a third map with the results of the evaluation (average,
> std) given to the areas of the first map.
>
> Is this possible in a simple way, or should I write something myself. I
> can't seem to find a premade function that does this or something close to
> it.

it is quit simple: 

1) change your 'patch map' with r.to.vect and v.to.rast into individually 
numbered patches

2) change your value_raster to integer and multiplication (e.g. '*100') is 
advisable: r.mapcalc "tmp1=int(value_raster*100)"

3) query your raster:
 r.statistics  base=patch_raster cover=tmp1 method=average 
out=value_raster --o

4) perhaps use r.mapcalc to revert the *100 modification in the new map


regards, Martin


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University of Wuerzburg
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