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) $

       Main index | Vector index | Topics index | Keywords index | Full index

       © 2003-2016 GRASS Development Team, GRASS GIS 7.0.3 Reference Manual

GRASS 7.0.3                                                                                     v.random(1grass)