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 [-v] input=string output=string  [--overwrite]
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17   Flags:
18       -v  Output verbosely
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20       --overwrite
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22   Parameters:
23       input=string
24           Elevation map
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26       output=string
27           Topographic index ln(a/tanB) map
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DESCRIPTION

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

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

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

56       Main algorithm sources are rewritten from GRIDATB.FOR.
57       Thanks to Keith Beven.
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59       GRASS port by Huidae Cho
60       Hydro Laboratory, Kyungpook National University, South Korea
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62       Last changed: $Date: 2007/01/17 16:35:59 $
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64       Full index
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68GRASS 6.2.2                                                        r.topidx(1)