## 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 (so, 20 XII 2014) $

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

© 2003-2015 GRASS Development Team, GRASS GIS 7.0.0 Reference Manual