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.

       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
       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: Thursday Aug 01 11:30:30 2024

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       © 2003-2024 GRASS Development Team, GRASS GIS 8.4.0 Reference Manual