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

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

10       raster, hydrology, wetness, topographic index
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SYNOPSIS

13       r.topidx
14       r.topidx --help
15       r.topidx input=name output=name  [--overwrite]   [--help]   [--verbose]
16       [--quiet]  [--ui]
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18   Flags:
19       --overwrite
20           Allow output files to overwrite existing files
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22       --help
23           Print usage summary
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25       --verbose
26           Verbose module output
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28       --quiet
29           Quiet module output
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31       --ui
32           Force launching GUI dialog
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34   Parameters:
35       input=name [required]
36           Name of input elevation raster map
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38       output=name [required]
39           Name for output topographic index raster map
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DESCRIPTION

42       r.topidx  creates  topographic  index (wetness index), ln(a/tan(beta)),
43       map from elevation map
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45       where
46       a: the area of the  hillslope  per  unit  contour  length  that  drains
47       through any point,
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49       tan(beta):  the  local  surface  topographic  slope  (delta vertical) /
50       (delta horizontal).
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52       Input maps may have NULL values.  For example, if you have a MASK for a
53       watershed  (basin  map from r.water.outlet), the following command will
54       create a masked elevation map (belev):
55       r.mapcalc "belev = if(isnull(basin), basin, elev)"
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57       r.stats -Anc prints out averaged statistics for topographic index.
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EXAMPLE

60       Running the command below will generate the topographic index map shown
61       in the figure:
62       g.region raster=elevation -p
63       r.topidx input=elevation output=topidx_elevation
64       Figure: topographic index map derived from elevation map
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REFERENCES

67       Cho,  H.,  2000.  GIS Hydrological Modeling System by Using Programming
68       Interface of GRASS. Master’s Thesis, Department of  Civil  Engineering,
69       Kyungpook National University, Korea.
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71       Moore,  I.D., R.B. Grayson, and A.R. Ladson, 1991. Digital Terrain Mod‐
72       eling: A Review of Hydrological, Geomorphological, and  Biological  Ap‐
73       plications.  Hydrological Processes 5:3-30.
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SEE ALSO

76        r.topmodel, r.water.outlet, r.mapcalc
77       Known issues
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AUTHORS

80       Huidae Cho
81       Hydro Laboratory, Kyungpook National University, South Korea
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83       Based on GRIDATB.FOR by Keith Beven.
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SOURCE CODE

86       Available at: r.topidx source code (history)
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88       Accessed: Mon Jun 20 16:46:34 2022
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90       Main  index  | Raster index | Topics index | Keywords index | Graphical
91       index | Full index
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93       © 2003-2022 GRASS Development Team, GRASS GIS 8.2.0 Reference Manual
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97GRASS 8.2.0                                                        r.topidx(1)
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