[GRASS-user] calculate mode value on moving window (with mapalgebra) with null value cells

[Marcello Gorini]

G. Allegri wrote:

I need to assign values to a the cells on the "border" of a raster. The
> inside and the outside are distinguished by having or not having null
> values assigned.
> I also need to keep the other cell values (internals) untouched.
>
>
 Hey,

Check out r.grow. I am pretty sure you can modify the example given in the
manual to find the borders of your raster. Something like:

# creates an inverted raster from your raster
> r.mapcalc "raster_inverted=if(isnull(raster,1,null())"
# grow this inverted raster by one cell
> r.grow in=raster_inverted out=raster_inverted_grown
# now both rasters overlap at the border, so you can do whatever you want
with it, for instance, extract it
> r.mapcalc "border=if(raster_inverted_grown==1 &&
isnull(raster)==0,raster,null())"

Hope it helps.

Cheers,
Marcello.
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