.TH r.topidx 1grass "" "GRASS 8.3.2" "GRASS GIS User's Manual"
.SH NAME
\fI\fBr.topidx\fR\fR  \- Creates a topographic index (wetness index) raster map from an elevation raster map.
.SH KEYWORDS
raster, hydrology, wetness, topographic index
.SH SYNOPSIS
\fBr.topidx\fR
.br
\fBr.topidx \-\-help\fR
.br
\fBr.topidx\fR \fBinput\fR=\fIname\fR \fBoutput\fR=\fIname\fR  [\-\-\fBoverwrite\fR]  [\-\-\fBhelp\fR]  [\-\-\fBverbose\fR]  [\-\-\fBquiet\fR]  [\-\-\fBui\fR]
.SS Flags:
.IP "\fB\-\-overwrite\fR" 4m
.br
Allow output files to overwrite existing files
.IP "\fB\-\-help\fR" 4m
.br
Print usage summary
.IP "\fB\-\-verbose\fR" 4m
.br
Verbose module output
.IP "\fB\-\-quiet\fR" 4m
.br
Quiet module output
.IP "\fB\-\-ui\fR" 4m
.br
Force launching GUI dialog
.SS Parameters:
.IP "\fBinput\fR=\fIname\fR \fB[required]\fR" 4m
.br
Name of input elevation raster map
.IP "\fBoutput\fR=\fIname\fR \fB[required]\fR" 4m
.br
Name for output topographic index raster map
.SH DESCRIPTION
\fIr.topidx\fR creates topographic index (wetness index), ln(a/tan(beta)), map from
elevation map
.PP
where
.br
a: the area of the hillslope per unit contour length that drains through any point,
.PP
.br
tan(beta): the local surface topographic slope (delta vertical) / (delta horizontal).
.PP
Input maps may have NULL values.  For example, if you have a MASK for
a watershed (basin map from \fIr.water.outlet\fR), the
following command will create a masked elevation map (belev):
.br
.nf
\fC
r.mapcalc \(dqbelev = if(isnull(basin), basin, elev)\(dq
\fR
.fi
.PP
\fIr.stats \-Anc\fR prints out averaged statistics for topographic index.
.SH EXAMPLE
Running the command below will generate the topographic index map shown in the figure:
.br
.nf
\fC
g.region raster=elevation \-p
r.topidx input=elevation output=topidx_elevation
\fR
.fi
.br
\fIFigure: topographic index map derived from elevation map\fR
.SH REFERENCES
Cho, H., 2000. GIS Hydrological Modeling System by Using Programming Interface
of GRASS. Master\(cqs Thesis, Department of Civil Engineering, Kyungpook National
University, Korea.
.PP
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.
.SH SEE ALSO
\fI
r.topmodel,
r.water.outlet,
r.mapcalc
\fR
.br
Known issues
.SH AUTHORS
Huidae Cho
.br
Hydro Laboratory, Kyungpook National University, South Korea
.PP
Based on GRIDATB.FOR by Keith Beven.
.SH SOURCE CODE
.PP
Available at:
r.topidx source code
(history)
.PP
Accessed: Friday Mar 08 07:34:47 2024
.PP
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.PP
© 2003\-2024
GRASS Development Team,
GRASS GIS 8.3.2 Reference Manual