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

[G. Allegri]

I'm already using your fast version for a big work on half the Italy
territory. Only your improvement let me make it with grass, so THANKS!

Giovanni

2008/10/10 Dylan Beaudette <dylan.beaudette at gmail.com>:
> 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
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