<p>Hi all, I'd like to report the results of testing I just did with the new r.watershed2 module from the addons svn. I am using the latest svn source version of grass6.4, compiled on a dual processor dell with 2 gigs ram, and running the latest ubuntu 8.10 OS. I used the dataset that I've used for all my testing and development for the LandDyn addon modules (up on svn addon server), and with which I have good knowlege of the results of hydrographic modeling with r.flow, r.terraflow, and old r.watershed. I A/B tested the old r.watershed module against the new r.watershed2 module wit this same dataset, and with same options enabled (except of course for "memory" option which is only available in new r.watershed2, and which I set to 1000). The input DEM is approximately 1.5 million cells (15meter resolution), and is of a single large watershed (areas outside watershed boundaries are NULL).</p>
<p>Results: both modules successfully produce quality output maps. In fact, when the output maps are compared (subtracted with mapcalc) there is absolutely NO DIFFERENCE between them. All values are the same. The main difference then between the modules is the speed at which they operate. Old r.watershed took about 1.5 minutes to finish, while the new r.watershed2 took ABOUT 5 SECONDS!!! This is an amazing increase in speed for exactly the same result!<br clear="all">
</p><p>I'd like to put my vote in for replacement of original r.watershed by r.watershed2 in current GRASS6.4 svn, especially because now I'd like to replace usage of r.terraflow in the LandDyn scripts with r.watershed2. This would greatly increase the speed, and perhaps the accuracy of those modules (r.landscape.evol modules).</p>
<p>Two minor suggestions for improvement, however. </p><p>1) neither version of r.watershed propagates NULL values. Currently, one must use a MASK to make sure wierd values aren't calculated for outmaps in NULL areas of the input map. A flag to ignore NULL areas would make alot of sense, and perhaps in GRASS7, make the default option be to ignore NULL's with a flag to reverse.</p>
<p>2) both versions have redundant options for outputing flow accumulation map: the output options "accumulation" and "visual" output the same map! The only difference between them is that "accumulation" lacks a color table (on display, all values are magenta), while "visual" has been assigned some custom set of color rules, so that it looks nice when displayed. Since no time is lost for color rule assinment, it does not make sense to allow for the option to create two otherwise identical maps. IMO, "visual" output option should be removed, and "accumulation" option should just output a properly colored map.</p>
<p></p><p>Cheers,</p><br>-- <br><br>Isaac I Ullah, M.A.<br><br>Archaeology PhD Student,<br>ASU School of Evolution and Social Change<br><br>Research Assistant,<br>Mediterranean Landscape Dynamics Project<br>***************************************************<br>
<a href="mailto:isaac.ullah@asu.edu">isaac.ullah@asu.edu</a><br><a href="mailto:ullah@archaeologist.com">ullah@archaeologist.com</a><br><br><a href="http://www.public.asu.edu/~iullah">http://www.public.asu.edu/~iullah</a><br>
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