[GRASS-user] r.mask vs g.region

[Huidae Cho]

Hello Rich,

g.region creates a rectangular computational region while r.mask can create
an irregular mask. If you use r.mask, any cells outside the mask will be
ignored, so you have to make sure that your mask is big enough to cover
your basin. In terms of computational time, r.mask can be faster depending
on what modules you need. For example, when you run flow accumulation, you
may save some time using r.mask because you don't have to calculate flow
accumulation outside your area of interest. If you use g.region that covers
your basin, you calculate flow accumulation outside the basin within the
rectangular region. So in general, I would say r.mask is preferred if and
only if the mask is correct.

Regards,
Huidae


On Tue, Jul 10, 2018 at 1:01 PM, Rich Shepard <rshepard at appl-ecosys.com>
wrote:

>   I have DEMs covering a large area and want to limit analyses to a single
> drainage basin. I can use 'g.region vect=basin_name' or 'r.mask
> vect=basin_name' and want to learn of differences by applying one in
> preference to tha other. Are there situations where one is preferred over
> the other? Does computational time differ between the two?
>
> TIA,
>
> Rich
>
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-- 
Huidae Cho, Ph.D., PE, M.ASCE, CFM, GISP
Senior Geospatial Engineer, MapAnything
Open Source GIS Developer, GRASS GIS Development Team
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