[GRASS-user] r.neighbour and r.mask

Glynn Clements glynn at gclements.plus.com
Tue Jul 7 09:44:21 EDT 2009

Milton Cezar Ribeiro wrote:

> Just suppose I have a very large - and irregular - region, and that
> I am running r.neighbors to compute some moving windows stats. As my
> region is irregular, many of central pixels will be NULL. If I use
> r.mask, it means that when I run r.neighbours the processing will be
> faster than when I not set r.mask (supposing that the north, south,
> west and east will be the same on both case)?

There's no point in using r.mask to mask out pixels which are already
null. The mask simply forces specific pixels to be read as null; to
the module, such nulls are indistinguishable from nulls in the
original data.

Glynn Clements <glynn at gclements.plus.com>

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