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
       boundaries  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)

SOURCE CODE

       Available at: r.surf.area source code (history)

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       © 2003-2019 GRASS Development Team, GRASS GIS 7.8.2 Reference Manual