[GRASS-dev] Re: Testing results of new r.watershed against r.terraflow

Isaac Ullah isaac.ullah at asu.edu
Wed Dec 3 13:42:30 EST 2008


Sorry, I transposed the links. The top link is the results using r.terraflow
in r.landscape.evol, and the bottom link is the results using r.watershed,
not vice versa. Also, I should note that these maps are the absolute value
of the 10th year dem with smoothing enabled minus the 10th year dem with no
smoothing.

On 12/3/08, Isaac Ullah <isaac.ullah at asu.edu> wrote:
>
> Here are some additional results of testing between new version of
> r.watershed and r.terraflow.
>
> *Time costs:*
>
> Map A (2.8 million cells), r.watershed is 52 seconds faster than
> r.terraflow
>
> Map B (21 millions cells), r.watershed is 2 minutes 58 seconds faster than
> r.terraflow
>
> *Accuracy in r.landscape.evol simulations:*
>
> Maps produced using r.watershed for flowacc show realistic values of
> erosion and deposition *with no smoothing* after 10 model cycles(1 cycle =
> 1 sim year). The difference between smoothed and unsmoothed maps is at
> maximum only .5 meters, and the diffs are dispersed topographically. Image
> link:
> http://www.public.asu.edu/~iullah/files/MEDLAND/smo_nosmo_diff_terraflw.png
>
> Maps produced using r.terraflow for flowacc show spikes as high as +/- 96
> meters (with no smoothing) after 10 model cycles. Spikes are concentrated in
> the channels, and diff between smoothed and un smoothed results also show
> anamolies are concetrated in the channels. Image link:
> http://www.public.asu.edu/~iullah/files/MEDLAND/smo_nosmo_diff_rwshd.png
>
> I am currently testing new r.watershed in a longterm model run (100 cycles)
> with no smoothing, and will report the results here. In r.lnadscape.evol for
> a 2.8 million cell map, the smoothing routine costs 23.5 seconds. Using new
> r.watershed with the smoothing turned on takes 1 minute 5.5 seconds. Without
> smoothing takes only 42 seconds. Using r.terraflow with smoothing takes 1
> min 57 seconds. Using r.terraflow without smoothing takes 1 minute 33
> seconds, but produces unusable results. Also, using r.watershed eliminates
> the need to run r.fill.dir before each model run--an additional time
> savings...
>
> 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
> ***************************************************




-- 

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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