[GRASS-dev] r.slope.aspect: one pixel less in the output at the border shrinks region extent in further calculations

Helmut Kudrnovsky hellik at web.de
Sun Jan 4 10:53:15 PST 2015

Dear Helena,

> 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. 

I agree with you that a reasonable estimate is better than the current

I've opened an enhancement ticket for this

> 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. 
> (you can compute the edge values e.g.in r.mapcalc). 

I'll have a look r.resamp.rst and r.mapcalc in the meantime.

> I am quite interested in the flat valley bottoms.

the authors [1] introduced a quite complex procedure to calculate an index
of valley bottom flatness, but it seems to be used especially in soil
science papers. I've used it a little bit for riverine landscape analysis.

in r.valley.bottom [1] DEM coarsening and smoothing as suggested by Gallant
& Dowling seems to work already; although a lot of code tweaking (especially
to choose/calculate thresholds independently of base DEM resolution, ...) is
still needed. 

testing and input is welcome.

"John C. Gallant and Trevor I. Dowling
A multiresolution index of valley bottom flatness for mapping depositional
WATER RESOURCES RESEARCH, VOL. 39, NO. 12, 1347, doi:10.1029/2002WR001426,


best regards
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