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

[Markus Metz]

On Tue, Jun 19, 2012 at 12:39 PM, G. Allegri <giohappy at gmail.com> wrote:
> 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...

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.

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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