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       r.average   -  Finds  the  average of values in a cover map within areas assigned the same
       category value in a user-specified base map.


       raster, statistics


       r.average help
       r.average [-c] base=name cover=name 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

           Name for output raster map


       r.average calculates the average value of data contained in a cover raster map  layer  for
       areas assigned the same category value in the user-specified base raster map layer.  These
       averaged values are stored in the category labels file associated with a  new  output  map
       layer.  The values to be averaged are taken from a user-specified cover map.  The category
       values for the cover map will be averaged, unless the -c flag is set.  If the -c  flag  is
       set, the values that appear in the category labels file for the cover map will be averaged
       instead (see example below).

       The output map is actually a reclass of the base  map  (see   r.reclass),  and  will  have
       exactly  the  same  category  values  as  the  base  map.  The averaged values computed by
       r.average are stored in the output map's category  labels  file.   The  base=  map  is  an
       existing  raster  map  layer  in the user's current mapset search path.  For each group of
       cells assigned the same category value in the base map, the values assigned these cells in
       the  cover map will be averaged.  The cover map is an existing raster map layer containing
       the values (in the form of cell category values or cell category labels)  to  be  averaged
       within each category of the base map.


       The  -c  option  requires  that the category label for each category in the cover map be a
       valid number, integer, or decimal.  To be exact,  if  the  first  item  in  the  label  is
       numeric, then that value is used. Otherwise, zero is used.  The following table covers all
       possible cases:

                category    value
                label       used by -c
                 .12          .12
                 .80 KF        .8
                 no data       0

       (This flag is very similar to the @ operator in r.mapcalc, and the user is  encouraged  to
       read the manual entry for r.mapcalc to see how it works there.)

       The  user  should  use  the  results of r.average with care.  Since this utility assigns a
       value to each cell which is based on global  information  (i.e.,  information  at  spatial
       locations  other  than  just  the location of the cell itself), the resultant map layer is
       only valid if the geographic region and mask settings are the same as  they  were  at  the
       time that the result map was created.

       Results are affected by the current region settings and mask.


       Assume  that farms is a map with 7 farms (i.e., 7 categories), and that soils.Kfactor is a
       map of soil K factor values with the following category file:
            cat  cat
            value     label
            0    no soil data
            1    .10
            2    .15
            3    .17
            4    .20
            5    .24
            6    .28
            7    .32
            8    .37
            9    .43

       r.average -c base=farms cover=soils.Kfactor

       will compute the average soil K factor for each farm, and store the result in  the  output
       map,  which will be a reclass of farms with category labels as follows (example
            cat  cat
            value     label
            1    .1023
            2    .1532
            3    .172
            4    .3872
            5    .003
            6    .28
            7    .2345


       g.region, r.category, r.clump,  r.describe,  r.mapcalc,  r.mfilter,  r.mode,  r.neighbors,
       r.reclass, r.statistics, r.stats


       Michael Shapiro, U.S. Army Construction Engineering Research Laboratory

       Last changed: $Date: 2008-05-16 12:09:06 -0700 (Fri, 16 May 2008) $

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