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Man Pages
r.topidx(1) GRASS GIS User's Manual r.topidx(1)

r.topidx - Creates a topographic index (wetness index) raster map from an elevation raster map.

raster, hydrology, wetness, topographic index

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

--overwrite

Allow output files to overwrite existing files
--help

Print usage summary
--verbose

Verbose module output
--quiet

Quiet module output
--ui

Force launching GUI dialog

input=name [required]

Name of input elevation raster map
output=name [required]

Name for output topographic index raster map

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.

Running the command below will generate the topographic index map shown in the figure:

g.region raster=elevation -p
r.topidx input=elevation output=topidx_elevation


Figure: topographic index map derived from elevation map

r.topmodel, r.water.outlet, r.mapcalc
Known issues

Cho, H., 2000. GIS Hydrological Modeling System by Using Programming Interface of GRASS. Master’s Thesis, Department of Civil Engineering, Kyungpook National University, Korea.

Moore, I.D., R.B. Grayson, and A.R. Ladson, 1991. Digital Terrain Modeling: A Review of Hydrological, Geomorphological, and Biological Applications. Hydrological Processes 5:3-30.

Huidae Cho
Hydro Laboratory, Kyungpook National University, South Korea

Based on GRIDATB.FOR by Keith Beven.

Available at: r.topidx source code (history)

Main index | Raster index | Topics index | Keywords index | Graphical index | Full index

© 2003-2021 GRASS Development Team, GRASS GIS 7.8.6 Reference Manual

GRASS 7.8.6

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