[GRASS-user] MAP Calculator mean of eight neighbors to interpolate 0 value in raster map

[Glynn Clements]

stephen sefick wrote:

> >> This does not quite work for my purposes.  The problem is the the 0
> >> values are in a 2 or 3 grid wide seam in between patched raster maps,
> >> so the value is lower than it should be using
> >>
> >> r.mapcalc "benning_dem=if(patch_benning==0,
> >> (patch_benning[-1,-1]+patch_benning[1,-1]+patch_benning[-1,0]+
> >> patch_benning[1,0]+patch_benning[-1,1]+patch_benning[1,1])/6,
> >> patch_benning)"
> >>
> >> any thoughts,
> >
> > Do you want the average of all of the surrounding values, or only the
> > non-zero values?
>
> only the no zero values.  I could probably do something like if
> patch_benning[-1,-1]>0 etc., but I don not know how to code the number
> of non-zero numbers in the divisor to get and average.

r.mapcalc "benning_dem = eval( \
	m = patch_benning, \
	numer =  m[-1,-1]+ m[-1,0]+ m[-1,1]+ m[0,-1]+ m[0,1]+ m[1,-1]+ m[1,0]+ m[1,1], \
	denom = !m[-1,-1]+!m[-1,0]+!m[-1,1]+!m[0,-1]+!m[0,1]+!m[1,-1]+!m[1,0]+!m[1,1], \
	if(m,m,numer/denom))

The "!" (logical "not") operator returns 1 if its operand is zero and
0 otherwise.

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