Provided by: grass-doc_6.4.3-3_all 
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) $
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