r.surf.area(1)

1r.surf.area(1)                Grass User's Manual               r.surf.area(1)
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NAME

6       r.surf.area  - Surface area estimation for rasters.
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KEYWORDS

9       raster
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SYNOPSIS

12       r.surf.area
13       r.surf.area help
14       r.surf.area input=string  [vscale=float]
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16   Parameters:
17       input=string
18           Raster file for surface
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20       vscale=float
21           Vertical scale
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DESCRIPTION

24       r.surf.area  Calculates area of regular 3D triangulated points (centers
25       of cells) in current region by adding areas of  triangles.   Therefore,
26       area  of  a  flat surface will be reported as (rows + cols -1)*(area of
27       cell) less than area of flat region due to a half row and  half  column
28       missing around the perimeter.
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NOTE

31       This  calculation  is heavily dependent on data resolution (think of it
32       as a fractal shoreline problem, the more resolution  the  more  detail,
33       the  more  area, etc).  This program uses the CURRENT GRASS REGION, not
34       the resolution of the map.  This is especially important  for  surfaces
35       with  NULL  values  and  highly  irregular edges.  The program does not
36       [currently] attempt to correct for the error introduced  by  this  edge
37       effect.
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39       This  version  actually  calculates  area twice for each triangle pair,
40       keeping a running minimum and maximum area depending on  the  direction
41       of the diagonal used.
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43       Reported  totals  are:  "Plan"  area  of NULL values within the current
44       GRASS region "Plan" area within calculation region (rows-1 *  cols-1  *
45       cellarea)  Average  of  the  minimum and maximum calculated 3d triangle
46       area within this region "Plan" area within current GRASS region (rows *
47       cols  *  cellarea)  Scaling  of calculated area to current GRASS region
48       (see NOTE)
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NOTES

51       r.surf.area works best when the surface being evaluated extends to  the
52       edges  of  the  current  GRASS region and the cell resolution is small.
53       Surfaces which are especially long and thin and have  highly  irregular
54       boudaries  will  tend  to have underestimated surface areas.  Setting a
55       high cell resolution (small area) will greatly reduce this impact,  but
56       will cause longer processing times.
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AUTHOR

63       Bill Brown, USACERL December 21, 1994
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65       Modified for floating point rasters and NULL values by Eric  G.  Miller
66       (October 17, 2000)
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68       Last changed: $Date: 2003/05/06 15:49:06 $
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70       Full index
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74GRASS 6.2.2                                                     r.surf.area(1)