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

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=nameA [required]
	   Name	of input elevation raster map

       output=nameA [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

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

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 Mod-
       eling: A	Review of Hydrological,	Geomorphological, and  Biological  Ap-
       plications.  Hydrological Processes 5:3-30.

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)

       Main  index  | Raster index | Topics index | Keywords index | Graphical
       index | Full index

       A(C) 2003-2020 GRASS Development	Team, GRASS GIS	7.8.3 Reference	Manual

GRASS 7.8.3							   r.topidx(1)

NAME | KEYWORDS | SYNOPSIS | DESCRIPTION | EXAMPLE | SEE ALSO | REFERENCES | AUTHORS | SOURCE CODE

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