NAME

       v.random  - Generates random 2D/3D vector points.

KEYWORDS

       vector, sampling, statistics, random, point pattern

SYNOPSIS

       v.random
       v.random --help
       v.random    [-zab]    output=name    npoints=integer    [restrict=name]     [layer=string]
       [cats=range]     [where=sql_query]      [zmin=float]      [zmax=float]      [seed=integer]
       [column=name]    [column_type=string]    [--overwrite]   [--help]   [--verbose]  [--quiet]
       [--ui]

   Flags:
       -z
           Create 3D output

       -a
           Generate n points for each individual area

       -b
           Do not build topology

       --overwrite
           Allow output files to overwrite existing files

       --help
           Print usage summary

       --verbose
           Verbose module output

       --quiet
           Quiet module output

       --ui
           Force launching GUI dialog

   Parameters:
       output=name [required]
           Name for output vector map

       npoints=integer [required]
           Number of points to be created

       restrict=name
           Name of input vector map
           Restrict points to areas in input vector

       layer=string
           Layer number or name (’-1’ for all layers)
           A single vector map  can  be  connected  to  multiple  database  tables.  This  number
           determines  which  table  to  use.  When used with direct OGR access this is the layer
           name.
           Default: -1

       cats=range
           Category values
           Example: 1,3,7-9,13

       where=sql_query
           WHERE conditions of SQL statement without ’where’ keyword
           Example: income < 1000 and inhab >= 10000

       zmin=float
           Minimum z height (needs -z flag or column name)
           Default: 0.0

       zmax=float
           Maximum z height (needs -z flag or column name)
           Default: 0.0

       seed=integer
           The seed to initialize the random generator. If not set the process ID is used

       column=name
           Name of column for z values
           Writes z values to column

       column_type=string
           Type of column for z values
           Options: integer, double precision
           Default: double precision

DESCRIPTION

       v.random randomly generates vector points within the current  region  using  the  selected
       random number generator.

       v.random  can  generate  also  3D  vector points or write random value to attribute table.
       Point height range or attribute value range is controlled  by  specifying  zmin  and  zmax
       values.   Both  z  values  are  included  in  range (zmin <= z <= zmax).  Generated random
       attribute value type can be controlled by column data type. Use INTEGER  column  type  for
       integers and DOUBLE PRECISION for floating point numbers. Integer values are calculated by
       rounding random floating point number.

       To produce repeatable results a random seed can be set using the option seed.

   Restriction to vector areas
       If an input vector map  with  areas  is  specified,  the  location  of  random  points  is
       restricted  to  the  selected  areas.  By  default,  the  requested  number  of points are
       distributed across all areas.

       If the -a flag is given, the requested number of points is generated for  each  individual
       area.  For  example, if 20 points should be generated and the input map has 100 individual
       areas, 2000 points will be generated in total.

EXAMPLES

       All examples use the North Carolina sample dataset.

       Generate 20 random points with binary attribute (only 0 or 1):
       v.random output=binary_random npoints=20 zmin=0 zmax=1 column=’binary INTEGER’
       Generate 20 random 3D points using a specific random seed:
       v.random seed=52 output=height_random npoints=40 zmin=110 zmax=170 -z

       Random points with different X, Y, and Z coordinates Get 20  random  samples  from  raster
       map:
       g.region -p raster=elevation
       v.random output=random_samples npoints=20
       v.db.addtable map=random_samples layer=1 columns=’cat INTEGER, sample DOUBLE PRECISION’
       v.what.rast vector=random_samples raster=elevation@PERMANENT layer=1 column=sample
       Generate 20 random points and sample attribute data from geology (vector) map:
       g.region -p vector=geology
       v.random output=random_samples npoints=20
       v.db.addtable map=random_samples layer=1 columns=’cat integer, geology varchar(100)’
       v.what.vect vector=random_samples layer=1 column=geology \
         qvector=geology@PERMANENT qlayer=1 qcolumn=label
       Generate 20 random points in forested areas
       g.region -p raster=landclass96
       r.to.vect -v input=landclass96 output=landclass96 type=area
       v.random input=landclass96 output=random_samples npoints=20 \
         where="label = ’forest’"
       Generate 20 random points in each forest patch
       g.region -p raster=landclass96
       r.to.vect -v input=landclass96 output=landclass96 type=area
       v.random input=landclass96 output=random_samples npoints=20 \
         where="label = ’forest’" -a

SEE ALSO

        g.region, r.random, v.perturb, v.sample, v.what.rast, v.what.vect

AUTHOR

       James Darrell McCauley <darrell@mccauley-usa.com>,
       when he was at: Agricultural Engineering Purdue University

       Last changed: $Date: 2014-12-20 06:05:23 +0100 (Sat, 20 Dec 2014) $

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