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 <[email protected]> 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 > > _______________________________________________ > grass-user mailing list > [email protected] > https://lists.osgeo.org/mailman/listinfo/grass-user -- 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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