r.topidx1grass
Creates a topographic index (wetness index) raster map from an elevation raster map.
Usage
r.topidx
r.topidx --help
r.topidx input=name
output=name
[--overwrite]
[--help]
[--verbose]
[--quiet]
[--ui]
Keywords
raster, hydrology, wetness, topographic index
Overview
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.
Examples
Running the command below will generate the topographic index map shown in the figure:
g.region raster=elevation -pr.topidx input=elevation output=topidx_elevation
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.
Source code
Available at: r.topidx source code (history)
Accessed: Monday Feb 24 17:50:56 2025
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© 2003-2025 GRASS Development Team, GRASS GIS 8.4.1 Reference Manual
Releases
10 releases since Debian 4.0 (Etch); the text changed 9 times.