Thanks all for your suggestions! I created a comparison of methods [1] which were mentioned. But unfortunately, the results are still very different (at least from my point of view). What do you think about it? What approach should be chosen?
[1] https://docs.google.com/document/d/15MyV-l2BH5agjN1T3LtQBotH7RJsIL_ 5K7exSZypTnQ/edit?usp=sharing 2018-05-02 22:17 GMT+02:00 Markus Metz <[email protected]>: > > > On Wed, May 2, 2018 at 8:29 PM, Anna Petrášová <[email protected]> > wrote: > > > > On Wed, May 2, 2018 at 2:21 PM, Markus Neteler <[email protected]> > wrote: > > > On Wed, May 2, 2018 at 7:13 PM, Martin Landa <[email protected]> > wrote: > > >> Hi, > > >> > > >> one of my colleague is dealing with flow accumulation calculation in > > >> GRASS, and comparing results with Esri ArcGIS (builtin Flow > > >> Accumulation [1]). Tool in ArcGIS to me knowledge uses D8, so we run > > >> r.watershed with -s flag and also -a flag to avoid negative values. > > >> Resultant values are very different. > > >> > > >> * Esri ArcGIS (range: 0 - 20741) > > >> * r.watershed -s (range: -34068 - 5697) > > >> * r.watershed -sa (1 - 34068) > > > > > > I'd suggest to look at the univariate statistics first (r.univar -e) > > > and compare that instead of min/max only. > > > > Also, r.watershed uses least-cost path, unlike the arcmap tool. Did > > you fill the depressions before running the arcmap tool? > > If you want to get nearly identical results, use r.hydrodem to remove > sinks from the DEM, then use this conditioned DEM as input for both ArcGIS > and r.watershed. Note that with D8 there is some randomness about where > surface flow will go to in case of several neighbors with the same > elevation. In any case, if surface accumulation of ArcGIS and r.watershed > differ, literature cited in the corresponding manuals should allow to > decide which method is more appropriate for the current task. > > Markus M > > > > > > Anna > > > > > > > > markusN > > > > > >> Do you have idea why results are so different? Thanks for any pointers > > >> in advance! Martin > > >> > > >> [1] http://desktop.arcgis.com/en/arcmap/10.5/tools/spatial- > analyst-toolbox/flow-accumulation.htm > > >> > > >> -- > > >> Martin Landa > > >> http://geo.fsv.cvut.cz/gwiki/Landa > > >> http://gismentors.cz/mentors/landa > > >> _______________________________________________ > > >> grass-user mailing list > > >> [email protected] > > >> https://lists.osgeo.org/mailman/listinfo/grass-user > > > > > > > > > > > > -- > > > Markus Neteler, PhD > > > http://www.mundialis.de - free data with free software > > > http://grass.osgeo.org > > > http://courses.neteler.org/blog > > > _______________________________________________ > > > grass-user mailing list > > > [email protected] > > > https://lists.osgeo.org/mailman/listinfo/grass-user > > _______________________________________________ > > grass-user mailing list > > [email protected] > > https://lists.osgeo.org/mailman/listinfo/grass-user > >
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