r.surf.area - GRASS GIS manual

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
NOTES
EXAMPLES
SEE ALSO
AUTHOR

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.

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:

"Plan" area of NULL values within the current GRASS region
"Plan" area within calculation region (rows-1 * cols-1 * cellarea)
Average of the minimum and maximum calculated 3d triangle area within this region
"Plan" area within current computational region (rows * cols * cellarea)
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)

Latest change: Tuesday Dec 17 20:17:20 2024 in commit: ab90c5e5a9b668894da360fa97ffd4a51a38931e