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<h2>NAME</h2>
<em><b>r.statistics</b></em> - Calculates category or object oriented statistics.
<h2>KEYWORDS</h2>
raster, statistics
<h2>SYNOPSIS</h2>
<b>r.statistics</b><br>
<b>r.statistics help</b><br>
<b>r.statistics</b> [-<b>c</b>] <b>base</b>=<em>name</em> <b>cover</b>=<em>name</em> <b>method</b>=<em>string</em> <b>output</b>=<em>name</em> [--<b>overwrite</b>] [--<b>verbose</b>] [--<b>quiet</b>]
<h3>Flags:</h3>
<DL>
<DT><b>-c</b></DT>
<DD>Cover values extracted from the category labels of the cover map</DD>
<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>base</b>=<em>name</em></DT>
<DD>Name of base raster map</DD>
<DT><b>cover</b>=<em>name</em></DT>
<DD>Name of cover raster map</DD>
<DT><b>method</b>=<em>string</em></DT>
<DD>Method of object-based statistic</DD>
<DD>Options: <em>diversity,distribution,average,mode,median,avedev,stddev,variance,skewness,kurtosis,min,max,sum</em></DD>
<DT><b>output</b>=<em>name</em></DT>
<DD>Resultant raster map (not used with 'distribution')</DD>
</DL>
<H2>DESCRIPTION</H2>
<EM>r.statistics</EM> is a tool to analyse exploratory statistics of a "cover
layer" according to how it intersects with objects in a "base layer". A
variety of standard statistical measures are possible (called "zonal statistics"
in some GIS).
All cells in the base layer are considered one object for the analysis. For
some applications, one will first want to prepare the input data so that
all areas of contiguous cell category values in the base layer are uniquely
identified, which can be done with <EM>r.clump</EM>.
<BR>
The available methods are the following (english - german):
<ul>
<li>distribution - Verteilung in Prozent</li>
<li>average - Durchschnitt</li>
<li>mode - Modalwert</li>
<li>median - Median</li>
<li>average deviation - Durchschnittliche Abweichung</li>
<li>standard deviation - Standardabweichung</li>
<li>variance - Varianz</li>
<li>skewness - Schiefe der Verteilung</li>
<li>kurtosis - Relative Abflachung (-) oder Zuspitzung (+)</li>
<li>minimum - Minimum</li>
<li>maximum - Maximum</li>
<li>sum - Summe</li>
</ul>
The calculations will be performed on each area of data of the
cover layers which fall within each unique value, or category, of the base layer.
<P>
Setting the <EM>-c</EM> flag the category lables of the covering raster
layer will be used. This is nice to avoid the GRASS limitation to interger
in raster maps because using category values floating point numbers can be
stored.
<P>
All calculations except "distribution" create an output layer. The output
layer is a reclassified version of the base layer with identical
category values, but modified category labels - the results of the calculations
are stored in the category labels of the output layer.
<P>
For distributions, the output is printed to the user interface (stdout).
If an output file name was specified, it will be ignored. The result will
be a text table with three columns.
In the first column are the category values of the base layer (a), in the second
column the associated value of the cover layers (b), and in the third column the
percentage of area in that base layer category (a) that falls into that row's
value in the cover layer(b). Example:
<div class="code"><pre>
1 124 23
1 201 47
1 273 30
2 101 5
2 152 16
2 167 60
2 187 19
.
.
.
</pre></div>
So for the first line in the output above, we see that 23% of the cells of the
base layer category 1 have a value of 124 in the cover layer.
To transfer the values stored as category labels into cell values,
<em>r.mapcalc</em> can be used ('@' operator).
<H2>EXAMPLES</H2>
Calculation of average elevation of each field in the Spearfish region:
<div class="code"><pre>
r.statistics base=fields cover=elevation.dem out=elevstats method=average
r.category elevstats
r.mapcalc "fieldelev=@elevstats"
r.univar fieldelev
</pre></div>
<H2>SEE ALSO</H2>
<EM>
<A HREF="r.average.html">r.average</A>,
<A HREF="r.clump.html">r.clump</A>,
<A HREF="r.mode.html">r.mode</A>,
<A HREF="r.median.html">r.median</A>,
<A HREF="r.mapcalc.html">r.mapcalc</A>,
<A HREF="r.neighbors.html">r.neighbors</A>,
<A HREF="r.univar.html">r.univar</A>
<A HREF="r.category">r.category</A>
</EM>
<H2>AUTHOR</H2>
Martin Schroeder, Geographisches Institut Heidelberg, Germany
<p><i>Last changed: $Date: 2008-02-19 21:18:46 +0100 (Tue, 19 Feb 2008) $</i></p>
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