[GRASS-user] Fwd: How to obtain selected adjacent pixel values?

[Nikos Alexandris]

(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.

@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?

Best, Nikos