Hi, the notes bellow would make sense to put on the wiki, where it should go? Martin
2014-03-04 21:34 GMT+01:00 Markus Metz <[email protected]>: > On Tue, Mar 4, 2014 at 7:25 PM, Mark Seibel <[email protected]> wrote: >>> Hi. >> >>> >>> is it possible in GRASS to perform something similar to "Topo to >>> Raster" as known in ArcGIS [1]? >>> >>> [1] >>> http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#//009z0000007m000000.htm >> >> Are there specific inputs of the "topo to raster" tool that are of >> importance for your application? >> >> Using contour lines as input, I have found the r.surf.nnbathy module to >> perform very well. > > Previously, contour lines created by land surveying provided more > detail than available DEMs. Nowadays (since SRTM of 2001), DEMs > provide more detail than contour lines and contour lines are usually > derived from a DEM. Therefore creating a DEM from contour lines which > if in doubt have been created using a DEM is no longer recommended, > rather use any DEM instead. > >> For (LiDAR) point data, my preference is v.surf.rst. >> The "topo to raster" tool alters the DEM by filling sinks. > > The ArcGIS reference for sink filling is Goodchild and Mark (1987). > ArcGIS thus ignores the literature of the last 27 years. According to > the ArcGIS documentation, "The program assumes that all unidentified > sinks are errors". Identified sinks are those supplied by the user. > Unfortunately for ArcGIS, unidentified sinks are not errors but > usually true terrain elevation, particularly in the year 1987 when > LIDAR was not yet available and DEMs were derived from radar. That > means that the elevation values surrounding sinks are erroneuos rather > than the sinks themselves. Two (of several) methods to deal with sinks > in a more realistic way are the minimum impact approach of Lindsay & > Creed (2005) which alters the DEM (implemented in GRASS as r.hydrodem) > and r.watershed which does not alter the DEM. > > In short, you should not use ArcGIS to perform hydrological analysis > or create a DEM for hydrological analysis because the ESRI tools use > methods from the 1980's. Doing something similar to "Topo to Raster" > as known in ArcGIS does not make sense. Rather use > RiverTools/Whitebox/TauDEM/GRASS. > > Markus M > > >> The arcgis >> approach alters the DEM so that their flow routing tool doesnt stop in every >> sink. My preference is to use the data as close to original source as >> possible, and let the superb GRASS flow and routing algorithms handle >> routing through the sinks automatically. >> >> If one wanted to mimic the arcgis method of filling sinks after >> interpolating, one could run iterations of r.fill.dir to make it >> depression-less. This isnt necessary with the hydrologic tools in GRASS >> because the r.watershed algorithm is intelligent enough to keep seeking the >> next lowest location the DEM. Add in the fact that r.watershed has MFD, and >> GRASS quickly surpasses the ESRI hydrologic toolset offerings. >> >> HTH, >> Mark >> >> _______________________________________________ >> grass-user mailing list >> [email protected] >> http://lists.osgeo.org/mailman/listinfo/grass-user -- Martin Landa * http://geo.fsv.cvut.cz/gwiki/Landa _______________________________________________ grass-user mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/grass-user
