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

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

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)

       Accessed: Tuesday Jun 27 11:13:14 2023

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       © 2003-2023 GRASS Development Team, GRASS GIS 8.3.0 Reference Manual