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r.topidx

NAME

r.topidx - Creates topographic index [ln(a/tan(beta))] map from elevation map.

KEYWORDS

raster

SYNOPSIS

r.topidx
r.topidx help
r.topidx input=name output=name [--overwrite] [--verbose] [--quiet]

Flags:

--overwrite

Allow output files to overwrite existing files

--verbose

Verbose module output

--quiet

Quiet module output

Parameters:

input=name

Input elevation map

output=name

Output topographic index map

DESCRIPTION

r.topidx creates topographic index (wetness index), ln(a/tan(beta)), map from elevation map

where
a: the area of the hillslope per unit contour length that drains through any point,

tan(beta): the local surface topographic slope (delta vertical) / (delta horizontal).

Input maps may have NULL values. For example, if you have a MASK for a watershed (basin map from r.water.outlet), the following command will create a masked elevation map (belev):
r.mapcalc "belev = if(isnull(basin), basin, elev)"

r.stats -Anc prints out averaged statistics for topographic index.

SEE ALSO

r.topmodel, r.water.outlet, r.mapcalc

REFERENCE

Moore, I.D., R.B. Grayson, and A.R. Ladson, 1991. Digital terrain modeling: A review of hydrological, geomorphological, and biological applications. Hydrol. Processes 5:3-30.

AUTHORS

Main algorithm sources are rewritten from GRIDATB.FOR.
Thanks to Keith Beven.

GRASS port by Huidae Cho
Hydro Laboratory, Kyungpook National University, South Korea

Last changed: $Date: 2007-01-17 17:35:29 +0100 (Wed, 17 Jan 2007) $

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