Sorry, a mistake in the additional time requirements for MFD on elev_lid1972_1m: r.watershed2 with SFD: 0.7 seconds r.watershed2 with MFD: 1.0 seconds
Markus Metz wrote: > I took the request for MFD support in r.watershed by Helena and Dylan to > heart and implemented it, but still need a few more days to clean up the > code, then I want to submit it as r.watershed2.mfd to grass-addons. > > A first result for flow accumulation is here: > http://markus.metz.giswork.googlepages.com/rw2_mfd_large.jpg > This output has been calculated from elev_lid1972_1m in the North > Carolina sample dataset. > > Please compare to the original result and flow accumulation of other > modules as available here: > http://www.grassbook.org/gallery/chapters/s050404f070_flow.jpg > a) old r.watershed > b) r.flow > c) r.terraflow with MFD > d) r.sim.water > > References: > original MFD algorithm, also referenced to by r.terraflow > Quinn, P., Beven, K., Chevallier, P., and Planchon, 0. 1991. The > prediction of hillslope flow paths for distributed hydrological > modelling using digital terrain models, Hydrol. Process., 5, 59-79. > > The algorithm of Quinn et al. (1991) was modified by Holmgren (1994) and > is implemented here: > Holmgren, P. 1994. Multiple flow direction algorithms for runoff > modelling in grid based elevation models: an empirical evaluation. > Hydrol. Process., 8, 327-334. > > I added a convergence factor after Holmgren (1994): a lower convergence > factor results in more diverging flow, output will be similar to > r.terraflow in MFD, a higher convergence factor will result in more > converging flow, getting more similar to, but not identical to SFD. > > Additional memory requirements are not noticeable ( <2 KB) and > independent of the region size, additional time required is a few > seconds for elev_lid1972_1m, increasing by a few more seconds with > higher convergence factor. > > The color coding suggested by Hamish with absolute logarithm works nice > for most outputs, I have hardcoded it for flow accumulation output. > The color coding of the example image above has been adjusted a bit to > show more detail, but abs log of rainbow looks nice too! > > Markus Metz > > _______________________________________________ > grass-dev mailing list > grass-dev@lists.osgeo.org > http://lists.osgeo.org/mailman/listinfo/grass-dev > > _______________________________________________ grass-dev mailing list grass-dev@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-dev