<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> <html> <head> <title>GRASS GIS: r.topidx</title> <meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1"> <link rel="stylesheet" href="grassdocs.css" type="text/css"> </head> <body bgcolor="white"> <img src="grass_logo.png" alt="GRASS logo"><hr align=center size=6 noshade> <h2>NAME</h2> <em><b>r.topidx</b></em> - Creates topographic index [ln(a/tan(beta))] map from elevation map. <h2>KEYWORDS</h2> raster <h2>SYNOPSIS</h2> <b>r.topidx</b><br> <b>r.topidx help</b><br> <b>r.topidx</b> <b>input</b>=<em>name</em> <b>output</b>=<em>name</em> [--<b>overwrite</b>] [--<b>verbose</b>] [--<b>quiet</b>] <h3>Flags:</h3> <DL> <DT><b>--overwrite</b></DT> <DD>Allow output files to overwrite existing files</DD> <DT><b>--verbose</b></DT> <DD>Verbose module output</DD> <DT><b>--quiet</b></DT> <DD>Quiet module output</DD> </DL> <h3>Parameters:</h3> <DL> <DT><b>input</b>=<em>name</em></DT> <DD>Input elevation map</DD> <DT><b>output</b>=<em>name</em></DT> <DD>Output topographic index map</DD> </DL> <H2>DESCRIPTION</H2> <EM>r.topidx</EM> creates topographic index (wetness index), ln(a/tan(beta)), map from elevation map <P> where <DL> <DD>a: the area of the hillslope per unit contour length that drains through any point, <P> <DD>tan(beta): the local surface topographic slope (delta vertical) / (delta horizontal). </DL> <P> Input maps may have NULL values. For example, if you have a MASK for a watershed (basin map from <EM>r.water.outlet</EM>), the following command will create a masked elevation map (belev): <div class="code"><pre> r.mapcalc "belev = if(isnull(basin), basin, elev)" </pre></div> <P> <EM>r.stats -Anc</EM> prints out averaged statistics for topographic index. <H2>SEE ALSO</H2> <EM><A HREF="r.topmodel.html">r.topmodel</A></EM>, <EM><A HREF="r.water.outlet.html">r.water.outlet</A></EM>, <EM><A HREF="r.mapcalc.html">r.mapcalc</A></EM> <h2>REFERENCE</h2> Moore, I.D., R.B. Grayson, and A.R. Ladson, 1991. Digital terrain modeling: A review of hydrological, geomorphological, and biological applications. Hydrol. Processes 5:3-30. <H2>AUTHORS</H2> Main algorithm sources are rewritten from GRIDATB.FOR. <BR> Thanks to Keith Beven. <P> GRASS port by <A HREF=mailto:grass4u gmail com>Huidae Cho</A><BR> Hydro Laboratory, Kyungpook National University, South Korea <p><i>Last changed: $Date: 2007-01-17 17:35:29 +0100 (Wed, 17 Jan 2007) $</i></p> <HR> <P><a href="index.html">Main index</a> - <a href="raster.html">raster index</a> - <a href="full_index.html">Full index</a></P> <P>© 2003-2008 <a href="http://grass.osgeo.org">GRASS Development Team</a></p> </body> </html>
