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r.topidx

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

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

Example:

r.topidx input=name output=name

grass.script.run_command("r.topidx", input, output, overwrite=False, verbose=False, quiet=False, superquiet=False)

Example:

gs.run_command("r.topidx", input="name", output="name")

Parameters

input=name [required]
    Name of input elevation raster map
output=name [required]
    Name for output topographic index raster map
--overwrite
    Allow output files to overwrite existing files
--help
    Print usage summary
--verbose
    Verbose module output
--quiet
    Quiet module output
--qq
    Very quiet module output
--ui
    Force launching GUI dialog

input : str, required
    Name of input elevation raster map
    Used as: input, raster, name
output : str, required
    Name for output topographic index raster map
    Used as: output, raster, name
overwrite: bool, optional
    Allow output files to overwrite existing files
    Default: False
verbose: bool, optional
    Verbose module output
    Default: False
quiet: bool, optional
    Quiet module output
    Default: False
superquiet: bool, optional
    Very quiet module output
    Default: False

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 raster mask set for a watershed (using 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.

Lat/long projects are not supported. If data is not projected, please create a new project with a projected coordinate reference system and reproject the data there. Please run r.topidx from that project.

EXAMPLE

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

r.topidx example
Figure: topographic index map derived from elevation map

REFERENCES

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.

SEE ALSO

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

AUTHORS

Huidae Cho
Hydro Laboratory, Kyungpook National University, South Korea

Based on GRIDATB.FOR by Keith Beven.

SOURCE CODE

Available at: r.topidx source code (history)
Latest change: Thursday Feb 13 11:55:34 2025 in commit ffc0b8c