Helmut, you can use r.resamp.rst which computes slope and aspect and does not shrink the region. But you may need to adjust the parameters to make sure it works well.
Another way would be to modify r.slope.aspect to compute the values at the edges - a second order polynomial min.square approximation is used to estimate the derivatives in r.slope.aspect (you get the well known differencing function when you do the math) and it can be used also to compute the values at the edge cells, but I had no luck convincing others that it is the right thing to do. I believe that any reasonable estimate is better than the current shrinking region (in r.flow we just propagate the same values to the edges), but that does not seem to be the consensus. Also, implementation for the edges is not straightforward because of how GRASS works with rows, but a smart developer could certainly do it (you can compute the edge values e.g.in r.mapcalc). I hope this clarifies it and may be helps a little bit. I am quite interested in the flat valley bottoms - here in NC they are often found as bottoms of abandoned, dried out mill ponds. Helena Helena Mitasova Professor at the Department of Marine, Earth, and Atmospheric Sciences and Center for Geospatial Analytics North Carolina State University Raleigh, NC 27695-8208 [email protected] http://geospatial.ncsu.edu/osgeorel/ "All electronic mail messages in connection with State business which are sent to or received by this account are subject to the NC Public Records Law and may be disclosed to third parties.” On Jan 4, 2015, at 7:54 AM, Helmut Kudrnovsky wrote: > Hi Pietro, > >> this is not a bug. > > I unterstand the same. my question is more about how to implemented the > mentioned iterative algorithm which uses coarser resolution by each step and > how to avoid an extent shrinking of e.g. about 400m with the coarsest > resolution. > > > > ----- > best regards > Helmut > -- > View this message in context: > http://osgeo-org.1560.x6.nabble.com/r-slope-aspect-one-pixel-less-in-the-output-at-the-border-shrinks-region-extent-in-further-calculatis-tp5179874p5179923.html > Sent from the Grass - Dev mailing list archive at Nabble.com. > _______________________________________________ > grass-dev mailing list > [email protected] > http://lists.osgeo.org/mailman/listinfo/grass-dev _______________________________________________ grass-dev mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/grass-dev
