Good evening Ken You should be right, the watershed has a reservoir. I will test it in another place, with a hillslope, then I will give feedback. Thank you for your comment!
Cumprimentos, *Valter Albino -* Geógrafo Físico, M.Sc. Modelação H&H / Riscos ambientais / OT&U www.valteralbino.wixsite.com/hydrodynamics Ken Mankoff <[email protected]> escreveu no dia quinta, 4/06/2020 à(s) 18:03: > Hi Valter, > > On Fri, May 29, 2020 at 3:43 AM Valter Albino <[email protected]> > wrote: > >> Suppose you compute the "r.surf.area"(1) to some raster file and find >> that the 3d area is smaller than your 2d area? >> What could be the problem? >> Note: >> The exercise was done with a 5 m cell size raster file, with 37 km2 >> watershed with a slope of 0,0341 m/m, within 7.8 version of GRASS GIS 7.8 >> console in a 3.12.3 QGIS [with this method the difference is higher (12 ha, >> comparing with ArcGIS)] and outside QGIS, in GRASS GIS GUI >> Thanks in advance >> > > Can you provide a small example, perhaps just a few grid cells, that > reproduces the problem? Also, it isn't clear if you see the same problem in > ArcGIS, QGIS, and GRASS, or just GRASS. > > How are you calculating the 2D area? Do you note in r.surf.area under > DESCRIPTION that it says " Therefore, area of a flat surface will be > reported as (rows + cols -1) * (area of cell) less than area of flat > region due to a half row and half column missing around the perimeter." and > does this explain what you're seeing? > > -k. >
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