[GRASS-user] r.surf.area

[Valter Albino]

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 <mankoff  gmail.com> escreveu no dia quinta, 4/06/2020 à(s)
18:03:

> Hi Valter,
>
> On Fri, May 29, 2020 at 3:43 AM Valter Albino <valteralbino  gmail.com>
> 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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