Provided by: grass-doc_6.4.3-3_all

#### 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.

```

#### SEEALSO

```       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) \$

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