[GRASS-dev] testing results of r.watershed2 against old r.watershed

[Isaac Ullah]

Markus Metz wrote:

In my personal opinion, flow accumulation of r.watershed is also more
realistic than flow accumulation of r.terraflow (SFD), but I have
admittedly not tested it in detail.


I just wanted to add that I have, in fact, compared the results of the
r.watershed with r.terraflow, as well as with r.flow. In my opinion,
r.watershed consistently gives more accurate results than either of the
other two. r.flow gives the worst results (for the kind of process modeling
that I am interested in at least), while r.terraflow provides somewhat
better results. Both modules produce results with "spikes" of high values
that do not correspond perfectly with real topographic changes (or perhaps
it is better to say that they overestimate changes in accumulation at
certain places on the landscape), but r.watershed does not do that. The only
reason I was not using the old r.watershed in my scripts was the time vs.
map size issue. It was impossible to build it in as a dependant if it would
make the modle hang for days if the input map was too big for it. However, I
am please to say that initial tests running my r.landscape.evol with new
r.watershed are VERY encouraging! Not only does the whole thing run faster,
the results are MUCH more realistic! I may even be able to remove a time
consuming "smoothing" routine from the module since it seems that I no
longer am creating the anomolous "spikes" in elevation change do to problems
in the flowacc map. This, I think, is a very good reason for focusing more
development "sweat" to perfecting r.watershed. For future reference, I am
more than happy to test out any changes to the module....

Cheers

-- 

Isaac I Ullah, M.A.

Archaeology PhD Student,
ASU School of Evolution and Social Change

Research Assistant,
Mediterranean Landscape Dynamics Project
***************************************************
isaac.ullah at asu.edu
ullah at archaeologist.com

http://www.public.asu.edu/~iullah
***************************************************
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