[GRASS-user] r.watershed.fast new version

[Dylan Beaudette]

On Thursday 09 October 2008, Markus Metz wrote:
> Hi all,
>
> some time ago I posted a new version of r.watershed with substantial
> speed increase, but still with slight differences in the outputs
> compared to the original version. This problem is solved, whether or not
> these differences in flow direction and flow accumulation were critical.
> Now the results in flow direction and flow accumulation are 100%
> identical to the original version. All other outputs are based on flow
> direction and flow accumulation and therefore also identical.
>
> The speed increase for the ram version is the same as with my first
> version: e.g. a region with 22,500,000 cells is processed in 1minute 6
> seconds, the original version needs 10 hours. The modified seg version
> (-m flag set) needs 16 minutes (North Carolina sample data, elevation
> resampled to 3 m). No idea how long the original seg version needs for
> such a region, more than a day I guess.
>
> The source code of r.watershed.fast available here
> http://markus.metz.giswork.googlepages.com/r.watershed_fast_version.tar.gz
>
> If you give this modified version a try, please let me know if it works
> or not, I tested it only on Linux 32bit and Linux 64bit.
>
> Markus

Fantastic news. This should be integrated back into GRASS given that the 
output now exactly matches the original. Perhap a temporary move to the GRASS 
addons page would be a good start.

Thanks for making this possible.

Cheers,
-- 
Dylan Beaudette
Soil Resource Laboratory
http://casoilresource.lawr.ucdavis.edu/
University of California at Davis
530.754.7341