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

[Milton Cezar Ribeiro]

I Glynn,

Thanks for the reply. I was thinking (and must confess, I was wishing) that
with r.mask those pixels that are outside of the mask (i.e. is NULL) can by
skiped during the processing.
Anyway, pretty thanks.

milton

2009/7/7 Glynn Clements <glynn at gclements.plus.com>

>
> 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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