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NAME

r.topidx - Creates topographic index map from elevation raster map.

KEYWORDS

raster, hydrology

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: 2011-11-08 03:29:50 -0800 (Tue, 08 Nov 2011) $


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