Sorry, I just need to tell you I'm gonna work on this next week, but I really don't want to discourage you waiting with no news.
Thank you all. 2013/6/30 Markus Metz <markus.metz.gisw...@gmail.com> > On Sun, Jun 30, 2013 at 3:31 PM, Nikos Alexandris > <n...@nikosalexandris.net> wrote: > > (cc-ing @MarkusMetz) > > > > Yasser Said Lopez de Olmos Reyes wrote: > > > >> > How could I obtain the differences between central pixel values and > >> > cardinal directions pixel values related with a central pixel? > >> > Or in a different manner, how to do this in grass gis? > > > >> > RASTER_OUT= round(abs((RASTER_IN - RASTER_IN_PUSHED_ONE_ROW_UP) + > >> > (RASTER_IN - RASTER_IN_PUSHED_ONE_ROW_DOWN) + (RASTER_IN - > >> > RASTER_IN_PUSHED_ONE_COLUMN_LEFT) + (RASTER_IN - > >> > RASTER_IN_PUSHED_ONE_COLUMN_RIGHT)) > > > > Nikos Alexandris wrote: > >> This boils down to calculating > >> (RASTER_IN - RASTER_IN_PUSHED_ONE_ROW_UP) + > >> (RASTER_IN - RASTER_IN_PUSHED_ONE_ROW_DOWN) + > >> (RASTER_IN - RASTER_IN_PUSHED_ONE_COLUMN_LEFT) + > >> (RASTER_IN - RASTER_IN_PUSHED_ONE_COLUMN_RIGHT) > >> > >> Please check the manual of r.mapcalc. There is > >> > >> --%<--- > >> THE NEIGHBORHOOD MODIFIER > > .. > >> --->%-- > > > >> which I think can be used to obtain what is asked. > >> So, for each of the off-current pixel, the modifiers would be like > > > >> RASTER_IN_PUSHED_ONE_ROW_UP: map[-1,0] > >> RASTER_IN_PUSHED_ONE_ROW_DOWN: map[1,0] > >> RASTER_IN_PUSHED_ONE_COLUMN_LEFT: map[0,-1] > >> RASTER_IN_PUSHED_ONE_COLUMN_RIGHT: map[0,1] > >> > >> I am not exactly sure about the implementation though. > > r.mapcalc "RASTER_OUT=round(abs((RASTER_IN - RASTER_IN[0,-1]) + \ > (RASTER_IN - > RASTER_IN[0,1]) + \ > (RASTER_IN - > RASTER_IN[-1,0]) + \ > (RASTER_IN - > RASTER_IN[1,0])))" > > Note that this is the same like round(abs(4 * RASTER_IN - > (RASTER_IN[0,-1] + RASTER_IN[0,1] + RASTER_IN[-1,0] + > RASTER_IN[1,0]))) > > If you are interested in the sum of the absolute differences, you will > need to use abs() for each difference. > > > > > @Yasser, if you implement this and think it is something that can be > justified > > as generically useful, why not ask @MarkusMetz if it is easy to include > in > > "r.neighbors" as yet another method? > > # prepare a weights file with the contents > 0 1 0 > 1 0 1 > 0 1 0 > > r.neighbors in=raster_in out=raster_cardinalsum weight=weights method=sum > > r.mapcalc "RASTER_OUT = round(abs(4 * RASTER_IN - raster_cardinalsum))" > > HTH, > > Markus M > -- Saludos, Yasser
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