r.topidx(1grass) | GRASS GIS User's Manual | r.topidx(1grass) |
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]
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)
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