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

       Huidae Cho
       Hydro Laboratory, Kyungpook National University, South Korea

       Based on GRIDATB.FOR by Keith Beven.

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.

       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:topographicindexmapderivedfromelevationmap

       raster, hydrology, wetness, topographic index

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

       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.

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

       Available at: r.topidx source code (history)

       Accessed: Friday Apr 04 01:19:43 2025

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       © 2003-2025 GRASS Development Team, GRASS GIS 8.4.1 Reference Manual

GRASS 8.4.1                                                                                     r.topidx(1grass)

r.topidxr.topidx--helpr.topidxinput=nameoutput=name  [--overwrite]  [--help]  [--verbose]  [--quiet]  [--ui]

   Flags:--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

   Parameters:input=name[required]
           Name of input elevation raster map

       output=name[required]
           Name for output topographic index raster map