Hi Laura, I've done some RUSLE3d calculations before, but always based on projected coordinate systems.
1) With r.watershed you seem to be on the right path, as trying to use r.flow on a geographic coordinate system gives me this error: "lat/long projection not supported by r.flow. Please use 'r.watershed' for calculating flow accumulation." However, I just tried by reprojecting elevation from north carolina sampledata (nc_basic_spm_grass7.zip) to geographic and the results are not the same before and after reprojection. I followed instructions in [1], page 46f. I don't know anything about reprojections so the error might lay there. But if your results are also very implausible, then maybe better try again with projected coordinate system. 2) I never tried slope length based USLE calculations and cannot answer this question. Page 158 ff in [2] explains many different approaches to RUSLE in GRASS GIS. Best regards, Martin sources: [1] http://grass.osgeo.org/sampledata/north_carolina/ [2] Markus Neteler and Helena Mitasova, 2008, Open Source GIS: A GRASS GIS Approach. Third Edition. -- Martin Zbinden Riedacker 523 3154 Rüschegg Heubach +41 78 628 28 82 -- Martin Zbinden Riedacker 523 3154 Rüschegg Heubach +41 78 628 28 82 2014-07-24 9:56 GMT+02:00 Scherer Laura <[email protected]>: > Dear all, > > > > I would like to calculate the slope length and steepness (LS) factor for > USLE using r.watershed with the parameter length.slope. I have two > questions: > > 1) Is it necessary to reproject my raster into a projected coordinate system > or can I leave it in latitude-longitude? > > 2) It is required to set a value for the threshold. Is it not possible to > get a value for each cell? If not, do I always have to delineate the > watersheds as well and the length.slope returned is the value at the outlet? > > > > Thanks in advance for any help. > > > > Best regards, > > Laura > > > _______________________________________________ > grass-user mailing list > [email protected] > http://lists.osgeo.org/mailman/listinfo/grass-user _______________________________________________ grass-user mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/grass-user
