1r.topidx(1)                   Grass User's Manual                  r.topidx(1)
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NAME

6       r.topidx  - Creates topographic index [ln(a/tan(beta))] map from eleva‐
7       tion map.
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KEYWORDS

10       raster
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SYNOPSIS

13       r.topidx
14       r.topidx help
15       r.topidx input=name output=name  [--overwrite]  [--verbose]  [--quiet]
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17   Flags:
18       --overwrite
19           Allow output files to overwrite existing files
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21       --verbose
22           Verbose module output
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24       --quiet
25           Quiet module output
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27   Parameters:
28       input=name
29           Input elevation map
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31       output=name
32           Output topographic index map
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DESCRIPTION

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

54       r.topmodel, r.water.outlet, r.mapcalc
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REFERENCE

57       Moore,  I.D., R.B. Grayson, and A.R. Ladson, 1991. Digital terrain mod‐
58       eling: A  review  of  hydrological,  geomorphological,  and  biological
59       applications. Hydrol. Processes 5:3-30.
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AUTHORS

62       Main algorithm sources are rewritten from GRIDATB.FOR.
63       Thanks to Keith Beven.
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65       GRASS port by Huidae Cho
66       Hydro Laboratory, Kyungpook National University, South Korea
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68       Last changed: $Date: 2007-01-17 17:35:29 +0100 (Wed, 17 Jan 2007) $
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70       Full index
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72       © 2003-2008 GRASS Development Team
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76GRASS 6.3.0                                                        r.topidx(1)