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

[Markus Metz]

On Tue, Jun 19, 2012 at 6:36 PM, G. Allegri <giohappy at gmail.com> wrote:
> Yes, with r.neighbors I woul chenge the values to NULL, but I don't know how
> to solve the problem of applying the filter only to the cells with a
> specific value (involving only the values of their neighbors).

r.neighbors followed by r.patch, no MASK? This will keep the valid
cells of the original map and only replace cells that are NULL in the
original map with values from the filtered map. E.g.

g.region -p rast=DEM
r.neighbors in=DEM out=DEM_filt method=mode
r.patch in=DEM,DEM_filt out=DEM_patched

> My border cells have assigned a 10000 value. I'm working on a DEM., so this
> fictious value is a way to code my borders. I want to apply the filter only
> on these cells, while leaving the others (not on the border) unaltered.
> With r.mapcalc I use an if() statement, but with r.neighbors I would need a
> MASK.

BTW, if the border problem arouse from reprojecting with a method
other than nearest, you can use in trunk as resampling method one of
bilinear_f,cubic_f,lanczos_f with r.proj to avoid the border effect.

Markus M

>
> giovanni
>
> 2012/6/19 Markus Metz <markus.metz.giswork at googlemail.com>
>>
>> On Tue, Jun 19, 2012 at 6:15 PM, G. Allegri <giohappy at gmail.com> wrote:
>> >> 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...
>>
>> You could replace 9999 (according to your first post the category of
>> border cells) with NULL, then run r.neighbors, without a MASK?
>>
>> Markus M
>>
>> >
>> > 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.
>> >> >>
>> >> >>
>> >> >>
>> >> >
>> >> >
>> >> > _______________________________________________
>> >> > grass-user mailing list
>> >> > grass-user at lists.osgeo.org
>> >> > http://lists.osgeo.org/mailman/listinfo/grass-user
>> >> >
>> >
>> >
>
>