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 12:09:06 -0700 (Fri, 16 May 2008) $

       Full index

       © 2003-2013 GRASS Development Team

GRASS 6.4.3                                                                                  r.surf.area(1grass)