NAME

       r.surf.area  - Prints estimation of surface area for raster map.

KEYWORDS

       raster, surface, statistics, area estimation

SYNOPSIS

       r.surf.area
       r.surf.area --help
       r.surf.area  map=name   [vscale=float]   [units=string]   [--help]  [--verbose]  [--quiet]
       [--ui]

   Flags:
       --help
           Print usage summary

       --verbose
           Verbose module output

       --quiet
           Quiet module output

       --ui
           Force launching GUI dialog

   Parameters:
       map=name [required]
           Name of raster map

       vscale=float
           Vertical scale
           Default: 1.0

       units=string
           Output units
           Default: square map units
           Options: miles, feet, meters, kilometers, acres, hectares

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.

NOTES

       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  module
       uses the current region settings, not the resolution of the raster map. This is especially
       important for surfaces with NULL values and highly irregular edges. The  module  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 computational region (rows * cols * cellarea)

       5      Scaling of calculated area to current region

       r.surf.area works best when the surface being  evaluated  extends  to  the  edges  of  the
       current  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.

EXAMPLES

       g.region -p raster=elevation
       r.surf.area map=elevation units=hectares
       Null value area ignored in calculation: 0.000000
       Plan area used in calculation: 20221.510000
       Surface area calculation(low, high, avg):
               20294.310421 20320.936368 20307.623395
       Current region plan area: 20250.000000
       Estimated region Surface Area: 20336.234719

SEE ALSO

        g.region, r.surf.idw, r.surf.fractal, r.surf.gauss, r.volume, r.slope.aspect, v.to.rast

AUTHOR

       Bill Brown, USACERL December 21, 1994
       Modified for floating point rasters and NULL values by Eric G. Miller (October 17, 2000)
       Updated for GRASS 7, and units option by  Martin  Landa,  Czech  Technical  University  in
       Prague, Czech Republic (October 2011)

       Last changed: $Date: 2014-12-27 23:51:00 +0100 (Sat, 27 Dec 2014) $

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