NAME

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

KEYWORDS

       raster, statistics

SYNOPSIS

       r.average
       r.average help
       r.average [-c] base=name cover=name output=name  [--overwrite]  [--verbose]  [--quiet]

   Flags:
       -c
           Cover values extracted from the category labels of the cover map

       --overwrite
           Allow output files to overwrite existing files

       --verbose
           Verbose module output

       --quiet
           Quiet module output

   Parameters:
       base=name
           Name of base raster map

       cover=name
           Name of cover raster map

       output=name
           Name for output raster map

DESCRIPTION

       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.

NOTES

       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.

EXAMPLE

       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
        Then

       r.average -c base=farms cover=soils.Kfactor output=K.by.farm

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

SEE ALSO

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

AUTHOR

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

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

       Full index

       © 2003-2013 GRASS Development Team

GRASS 6.4.3                                                                                    r.average(1grass)