NAME

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

KEYWORDS

       raster, hydrology, wetness, topographic index

SYNOPSIS

       r.topidx
       r.topidx --help
       r.topidx input=name output=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

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 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.

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
       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)

       Accessed: Tuesday Jun 27 11:13:18 2023

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       © 2003-2023 GRASS Development Team, GRASS GIS 8.3.0 Reference Manual