trusty (1) r.univar.1grass.gz

NAME

       r.univar  - Calculates univariate statistics from the non-null cells of a raster map.

KEYWORDS

       raster, statistics

SYNOPSIS

       r.univar
       r.univar help
       r.univar   [-get]   map=name[,name,...]   [zones=name]    [output=name]    [percentile=float[,float,...]]
       [fs=character]   [--verbose]  [--quiet]

   Flags:
       -g
           Print the stats in shell script style

       -e
           Calculate extended statistics

       -t
           Table output format instead of standard output format

       --verbose
           Verbose module output

       --quiet
           Quiet module output

   Parameters:
       map=name[,name,...]
           Name of input raster map(s)

       zones=name
           Raster map used for zoning, must be of type CELL

       output=name
           Name for output file (if omitted or "-" output to stdout)

       percentile=float[,float,...]
           Percentile to calculate (requires extended statistics flag)
           Options: 0-100
           Default: 90

       fs=character
           Field separator
           Special characters: space, comma, tab
           Default: |

DESCRIPTION

       r.univar calculates the univariate statistics of one or several raster map(s). This includes  the  number
       of  cells counted, minimum and maximum cell values, range, arithmetic mean, population variance, standard
       deviation, and coefficient of variation. Statistics are calculated  separately  for  every  category/zone
       found  in  the  zones  input map if given.  If the -e extended statistics flag is given the 1st quartile,
       median, 3rd quartile, and given percentile are calculated.  If the -g  flag  is  given  the  results  are
       presented  in  a  format  suitable  for  use  in a shell script.  If the -t flag is given the results are
       presented in tabular format with the given field separator. The table can immediately be converted  to  a
       vector  attribute  table  which  can  then  be linked to a vector, e.g. the vector that was rasterized to
       create the zones input raster.

       When multiple input maps are given to r.univar, the overall statistics are calculated. This is useful for
       a  time  series  of  the  same  variable,  as well as for the case of a segmented/tiled dataset. Allowing
       multiple raster maps to be specified saves the user from using a temporary raster map for the  result  of
       r.series or r.patch.

NOTES

       As  with  most  GRASS raster modules, r.univar operates on the raster array defined by the current region
       settings, not the original extent and resolution of the input map. See g.region.

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

       Without a zones input raster, the r.quantile module will be significantly more efficient for  calculating
       percentiles with large maps.

EXAMPLE

       Calculate  the  raster statistics for zones within a vector map coverage and upload the results for mean,
       min and max back to the vector map:
       #### set the raster region to match the map
       g.region vect=fields res=10 -ap
       #### create rasterized version of vector map
       v.to.rast in=fields out=fields.10m use=cat type=area labelcolumn=label
       r.colors fields.10m color=random
       #### perform analysis
       r.univar -t map=elevation.10m zones=fields.10m | \
         cut -f1,5,6,8 -d'|' > fields_stats.txt
       #### populate vector DB with stats
       # create working copy of vector map
       g.copy vect=fields,fields_stats
       # create new attribute columns to hold output
       v.db.addcol map=fields_stats \
         columns='mean_elev DOUBLE PRECISION, min_elev DOUBLE PRECISION, max_elev DOUBLE PRECISION'
       # create SQL command file, and execute it
       sed -e '1d' fields_stats.txt | awk -F'|' \
         '{print "UPDATE fields_stats SET min_elev = "$2", max_elev = "$3", \
         mean_elev = "$4" WHERE cat = "$1";"}' \
          > fields_stats_sqlcmd.txt
       db.execute input=fields_stats_sqlcmd.txt
       #### view completed table
       v.db.select fields_stats

TODO

       mode, skewness, kurtosis

SEE ALSO

        g.region, r3.univar, r.average, r.median, r.mode, r.quantile, r.sum,  r.series,  r.stats,  v.rast.stats,
       r.statistics, v.univar

AUTHORS

       Hamish Bowman, Otago University, New Zealand
       Extended statistics by Martin Landa
       Multiple input map support by Ivan Shmakov
       Zonal loop by Markus Metz

       Last changed: $Date: 2012-08-14 02:11:23 -0700 (Tue, 14 Aug 2012) $

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       © 2003-2013 GRASS Development Team