Hi all, r.watershed in trunk r42236 has a new option to beautify flat areas, activated with a new -b flag, works with both SFD and MFD. The method is adapted from Garbrecht & Martz (1997).
The justification for the new option is that some regard straight flow lines in flat areas as an issue, e.g. Nardi et al (2008), Hydrogeomorphic properties of simulated drainage patterns using digital elevation models: the flat area issue http://dx.doi.org/10.1623/hysj.53.6.1176 For r.watershed, this is not that much of an issue because it does not create flat areas by sink filling. For naturally flat areas like lakes and broad rivers, it is not possible to determine the "correct" drainage direction only from a DEM, information about river and lake bottom would be needed to more accurately determine flow direction, but DEMs only show water surface (apart from bathymetry). Therefore I chose to describe the new option as "Beautify flat areas" and not as "correct flat areas". The new option is currently only implemented for the all in memory mode, and it requires more memory and more time. Contrary to other implementations, this new one modifies elevation values only temporarily to adjust drainage direction, flow is accumulated using the original elevation values. I'm not really convinced about this option, but since methods to modify flat areas appear regularly in the literature, I added one. If there is no strong support for the new option, I would remove it again. I guess it's mostly useful to produce pretty maps. Markus M _______________________________________________ grass-user mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/grass-user
