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In mountainous terrain on a sloping surface the planimetric land area
is less than the actual surface area on the ground. Is there an easy
way to use a DEM in GRASS to find the actual surface area? Maybe I'm
asking for a 3-D GIS...
Bill
bakerwl@uwyo.edu
Interesting problem. It should be possible to use r.mapcalc to look for four
neighboring DEM measurements, calculate distances and angles along the
surface between them, and the surface area of the enclosed lozenge from
that. This would create a new map, which can then be used to derive
aggregate surface measurements a la r.average.
Martijn
p.m.van-leusen@bham.ac.uk
>
> In mountainous terrain on a sloping surface the planimetric land area
> is less than the actual surface area on the ground. Is there an easy
> way to use a DEM in GRASS to find the actual surface area? Maybe I'm
> asking for a 3-D GIS...
>
> Bill
> bakerwl@uwyo.edu
>
Interesting problem. It should be possible to use r.mapcalc to look for four
neighboring DEM measurements, calculate distances and angles along the
surface between them, and the surface area of the enclosed lozenge from
that. This would create a new map, which can then be used to derive
aggregate surface measurements a la r.average.
Martijn
p.m.van-leusen@bham.ac.uk
I missed the original thread, and perhaps I don't understand the problem,
but I would think that area of a sloping cell could be found by:
(CELL WIDTH)^2/cos(slope)
r.average would then do the rest.
Steve King
Hydrologist 10159 East 11th St., Suite 300
NOAA, National Weather Service Tulsa, Oklahoma 74128-3050
Arkansas-Red Basin River Forecast Center Off: (918)832-4109
sbk@awips1.abrfc.noaa.gov FAX: (918)832-4101