valteralbino at gmail.com
Thu Jun 4 15:10:40 PDT 2020
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
Thank you for your comment!
*Valter Albino -* Geógrafo Físico, M.Sc.
Modelação H&H / Riscos ambientais / OT&U
Ken Mankoff <mankoff gmail.com> escreveu no dia quinta, 4/06/2020 à(s)
> Hi Valter,
> On Fri, May 29, 2020 at 3:43 AM Valter Albino <valteralbino gmail.com>
>> 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?
>> 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?
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