negative buffer, inward area buffer

[Andreas Lange]

Hi grassers,

i need a negative buffer (inward area buffer) for a category of a raster
map.

r.buffer itself does not allow to specify simply a negative value for
the buffering. 

I managed to calculate such a buffer with the combination of a
'reversed' map (reclassifying 1 to 0 and 0 to 1), a buffer around the
areas of this map and a r.mapcalc calculation to subtract this buffer
from the original map. But this is computationally very expensive and
the calculation of the buffer for the 'inverse' map needs a very long
time for complicated maps. 

So i wonder if there is a simpler way to implement this.

Any hints?

Thank you in advance,

Andreas
-- 
Andreas Lange, 65187 Wiesbaden, Germany, Tel. +49 611 807850
Andreas.Lange at Rhein-Main.de - A.C.Lange at GMX.net