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

[G. Allegri]

Hi Marcello,
thanks, but my problem is not finding the border. I already have it (with
its own category) but assigning it the value from the surrounding (not
null) value, e.g. max/min/etc.
The problem with kernel filters/moving windows is that they do not filter
out null values...

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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