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r.surf.area - Surface area estimation for rasters.
r.surf.area input=string [vscale=float] [--verbose] [--quiet]
- Raster file for surface
- Vertical scale
r.surf.area Calculates area of regular 3D triangulated points
(centers of cells) in current region by adding areas of triangles.
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
This calculation is heavily dependent on
data resolution (think of it as a fractal shoreline problem, the more
resolution the more detail, the more area, etc). This program uses the
CURRENT GRASS REGION, not the resolution of the map. This is
especially important for surfaces with NULL values and highly
irregular edges. The program does not [currently] attempt to correct for
the error introduced by this edge effect.
This version actually calculates area twice for each triangle pair,
keeping a running minimum and maximum area depending on the
direction of the diagonal used.
Reported totals are:
- "Plan" area of NULL values within the current GRASS region
- "Plan" area within calculation region (rows-1 * cols-1 * cellarea)
- Average of the minimum and maximum calculated 3d triangle area
within this region
- "Plan" area within current GRASS region (rows * cols * cellarea)
- Scaling of calculated area to current GRASS region (see
r.surf.area works best when the surface being evaluated extends
to the edges of the current GRASS region and the cell resolution is small.
Surfaces which are especially long and thin and have highly irregular
boudaries will tend to have underestimated surface areas. Setting a
high cell resolution (small area) will greatly reduce this impact, but will
cause longer processing times.
Bill Brown, USACERL December 21, 1994
Modified for floating point rasters and NULL values by
Eric G. Miller (October 17, 2000)
Last changed: $Date: 2008-05-16 12:09:06 -0700 (Fri, 16 May 2008) $
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