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       r.statistics  - Calculates category or object oriented statistics.


       raster, statistics


       r.statistics help
       r.statistics   [-c]  base=name  cover=name  method=string   [output=name]    [--overwrite]
       [--verbose]  [--quiet]

           Cover values extracted from the category labels of the cover map

           Allow output files to overwrite existing files

           Verbose module output

           Quiet module output

           Name of base raster map

           Name of cover raster map

           Method of object-based statistic

           Resultant raster map (not used with 'distribution')


       r.statistics 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 r.clump.
       The available methods are the following (english - german):

                     distribution - Verteilung in Prozent

                     average - Durchschnitt

                     mode - Modalwert

                     median - Median

                     average deviation - Durchschnittliche Abweichung

                     standard deviation - Standardabweichung

                     variance - Varianz

                     skewness - Schiefe der Verteilung

                     kurtosis - Relative Abflachung (-) oder Zuspitzung (+)

                     minimum - Minimum

                     maximum - Maximum

                     sum - Summe
       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.

       Setting the -c 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.

       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.

       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:
       1   124  23
       1   201  47
       1   273  30
       2   101  5
       2   152  16
       2   167  60
       2   187  19
        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, r.mapcalc can be used ('@' operator).


       Calculation of average elevation of each field in the Spearfish region:
       r.statistics base=fields cover=elevation.dem out=elevstats method=average
       r.category elevstats
       r.mapcalc "fieldelev=@elevstats"
       r.univar fieldelev


        r.average, r.clump, r.mode, r.median, r.mapcalc, r.neighbors, r.univar r.category


       Martin Schroeder, Geographisches Institut Heidelberg, Germany

       Last changed: $Date: 2011-11-08 03:29:50 -0800 (Tue, 08 Nov 2011) $

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