NAME¶
r.surf.area - Surface area estimation for rasters.
KEYWORDS¶
raster, statistics
SYNOPSIS¶
r.surf.area
r.surf.area help
r.surf.area input=
string [
vscale=
float]
[--
verbose] [--
quiet]
Parameters:¶
- input=string
-
Raster file for surface
- vscale=float
-
Vertical scale
DESCRIPTION¶
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
perimeter.
NOTE¶
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:
- 1
- "Plan" area of NULL values within the current GRASS region
- 2
- "Plan" area within calculation region (rows-1 * cols-1 *
cellarea)
- 3
- Average of the minimum and maximum calculated 3d triangle area within this
region
- 4
- "Plan" area within current GRASS region (rows * cols *
cellarea)
- 5
- Scaling of calculated area to current GRASS region (see NOTE)
NOTES¶
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.
SEE ALSO¶
r.sum,
r.surf.idw,
r.surf.idw2,
r.surf.fractal,
r.surf.gauss,
r.volume,
v.to.rast,
r.slope.aspect,
g.region
AUTHOR¶
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 21:09:06 +0200 (Fri, 16 May 2008) $
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