[GRASS-user] counting cells equal center cell on window

[Glynn Clements]

Milton Cezar Ribeiro wrote:

> I have a raster map with categorical values.
> I have many occurrence of alone-pixels, where all neighbours
> are different from a central pixels. So I need to change all pixels
> that differ from alll its neighbours for the "mode" value.
> 
> I know that "r.neighbours ..method=mode" return the mode value.
> Now I need to identify only those pixels that differ from neighbours.
> I think one way is count all occurrence the value of central pixel
> on a windows (like 3x3, 5x5), and attrib it on a bynary map, where
> "ones" is for those positons where central pixels have frequency 1,
> and "zeros" for those potisions where central pixels have frequency >1.

Maybe you want method=interspersion:

       interspersion
	   The percentage of cells containing values  which  differ  from  the
	   values assigned to the center cell in the neighborhood, plus 1.  In
	   the above example, the interspersion is:
	   5/8 * 100 + 1 = 63.5
	   The result is rounded to the nearest integer (in this case 64).

-- 
Glynn Clements <glynn at gclements.plus.com>