NAME
r.surf.area - Surface area estimation for rasters.
(GRASS Raster Program)
SYNOPSIS
r.surf.area
r.surf.area help
r.surf.area input=name [vscale=value]
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:
- "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
NOTE)
The program will be run non-interactively if the user specifies
the program parameter values and desired flag settings on the
command line, using the form:
-
r.surf.area input=name [vscale=value]
Alternately, the user can simply type r.surf.area on the command line,
without program arguments. In this case, the user will be prompted for
needed inputs and option choices using the standard GRASS user interface
described in the manual entry for
parser
.
Parameters:
- input=name
- Name of an existing raster map layer to use for the calculation.
- vscale=value
- Optional vertical scaling value to use in surface area calculation.
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.
r.surf.area
SEE ALSO
r.surf.idw
r.surf.idw2
s.surf.idw
r.surf.fractal
r.surf.gauss
v.to.rast
r.slope.aspect
g.region
parser
AUTHOR
Bill Brown, USACERL December 21, 1994
Modified for floating point rasters and NULL values by
Eric G. Miller (October 17, 2000)