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

[G. Allegri]

>
> AFAICT, r.neighbors ignores NULL values and assigns the new value from
> the surrounding non-NULL values. You could then patch your original
> map with the output of r.neighbors.
>

I have considered r.neighbors but I need to apply the filter only to some
specific categories (border cells in my case). A MASK wouldn't solve my
problem, because it would mask the neighbors...

giovanni



>
> HTH,
>
> Markus M
>
> >
> > giovanni
> >
> >
> > 2012/6/19 Marcello Gorini <gorini at gmail.com>
> >>
> >>
> >>
> >> 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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> >
>
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