NAME

       v.rast.stats   -  Calculates  univariate  statistics  from  a  raster  map based on vector
       polygons and uploads statistics to new attribute columns.

KEYWORDS

       vector, raster, statistics

SYNOPSIS

       v.rast.stats
       v.rast.stats help
       v.rast.stats   [-ce]   vector=name     [layer=integer]     raster=name    colprefix=string
       [percentile=integer]   [--verbose]  [--quiet]

   Flags:
       -c
           Continue if upload column(s) already exist

       -e
           Calculate extended statistics

       --verbose
           Verbose module output

       --quiet
           Quiet module output

   Parameters:
       vector=name
           Name of vector polygon map

       layer=integer
           A  single  vector  map  can  be  connected  to  multiple  database tables. This number
           determines which table to use
           Default: 1

       raster=name
           Name of raster map to calculate statistics from

       colprefix=string
           Column prefix for new attribute columns

       percentile=integer
           Percentile to calculate (requires extended statistics flag)
           Options: 0-100
           Default: 90

DESCRIPTION

       v.rast.stats calculates basic univariate statistics from a raster map only for  the  parts
       covered  by  the specified vector map.  The vector map will be rasterized according to the
       raster map resolution.  Then univariate statistics  are  calculated  per  vector  category
       (cat) from the raster map and the results uploaded to the vector map attribute table.  New
       columns are generated in the attribute table if not already present.

       Nine columns are generated (n, min, max, range, mean, stddev,  variance,  coeff_var,  sum)
       according  to the output of r.univar.  If the -e extended statistics flag is given the 1st
       quartile, median, 3rd quartile, and given percentile are also calculated.

NOTES

       The module may take a long time to run if the raster region contains  a  large  number  of
       cells. In this case the --verbose flag may be used to track progress.

       The  script  stops  if  a  (prefixed)  upload  column is already present in the vector map
       attribute table, unless otherwise instructed with the -c continue flag. The column  prefix
       will be separated from the statistic name with an underscore. For example with a prefix of
       "elev" the sum column will be named elev_sum.

       If a DBF database is being used,  note  that  column  names  are  restricted  by  the  DBF
       specification to 10 characters. Therefore it is advised to be economical in the use of the
       column prefix when using DBF as any additional characters will be chopped off.

       If a MASK is present, it will be restored after the script finished.  The  script  changes
       temporarily to the resolution of the given raster map.

       Large  amounts  of  system memory can be used when the -e extended statistics flag is used
       with a very large region setting. If the region is too large  the  module  should  display
       memory allocation errors.  Basic statistics can be calculated using any size input region.

EXAMPLES

       Example to upload DEM statistics to ZIP codes vector map (North Carolina sample dataset):
       g.copy vect=zipcodes_wake,myzipcodes_wake
       # set computational region to DEM:
       g.region rast=elevation -p
       # calculate DEM statistics, upload to vector map table:
       v.rast.stats myzipcodes_wake raster=elevation colprefix=elev
       # verify results:
       v.info -c myzipcodes_wake
       v.db.select myzipcodes_wake
       v.univar myzipcodes_wake column=elev_range type=centroid

SEE ALSO

        r.univar, v.univar, v.what.rast, v.what.vect

AUTHOR

       Markus Neteler, CEA (for the EDEN EU/FP6 Project)

       Last changed: $Date: 2011-11-08 01:42:51 -0800 (Tue, 08 Nov 2011) $

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       © 2003-2013 GRASS Development Team