NAME

       v.perturb  - Random location perturbations of vector points.

KEYWORDS

       vector, geometry, statistics, random, point pattern, level1

SYNOPSIS

       v.perturb
       v.perturb --help
       v.perturb       [-b]       input=name        [layer=string]       output=name       [distribution=string]
       parameters=float[,float,...]  [minimum=float]    [seed=integer]    [--overwrite]   [--help]   [--verbose]
       [--quiet]  [--ui]

   Flags:
       -b
           Do not build topology
           Advantageous when handling a large number of points

       --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:
       input=name [required]
           Name of input vector map
           Or data source for direct OGR access

       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

       output=name [required]
           Name for output vector map

       distribution=string
           Distribution of perturbation
           Options: uniform, normal
           Default: uniform

       parameters=float[,float,...] [required]
           Parameter(s) of distribution
           If the  distribution  is  uniform,  only  one  parameter,  the  maximum,  is  needed.  For  a  normal
           distribution, two parameters, the mean and standard deviation, are required.

       minimum=float
           Minimum deviation in map units
           Default: 0.0

       seed=integer
           Seed for random number generation
           Default: 0

DESCRIPTION

       v.perturb reads a vector map of points and writes the same points but perturbs the eastings and northings
       by adding either a uniform or normal delta value. Perturbation means that a variating  spatial  deviation
       is added to the coordinates.

NOTES

       The  uniform  distribution  is always centered about zero.  The associated parameter is constrained to be
       positive and specifies the maximum of the distribution; the minimum is the negation of that parameter. Do
       perturb into a ring around the center, the minimum parameter can be used.

       Usually,  the  mean  (first  parameter)  of  the  normal  distribution is zero (i.e., the distribution is
       centered at zero). The standard deviation (second parameter) is naturally constrained to be positive.

       Output vector points are not guaranteed to be contained within the current geographic region.

EXAMPLES

   Random, uniformly distributed selection
       To create a random, uniformly distributed selection of possible new points with a radius of  100,000  map
       units, use the following command:
       v.perturb input=comm_colleges output=uniform_perturb parameters=100000
       Your map should look similar to this figure:
       Figure: Map showing the actual community college points and uniformly random chosen points.

   Normal distributed selection
       For a normal distribution with a mean of 5000 and standard deviation of 2000, use the following command:
       v.perturb input=comm_colleges output=normal_perturb distribution=normal parameters=5000,2000
       Figure:  Map  showing  the actual community college points and normally random chosen and colored points.
       Notice that each point is closer to the original point.

   Normal distributed selection with a minimum value
       In order to include a minimum value of 500, use the following command:
       v.perturb input=comm_colleges output=min_perturb distribution=normal parameters=100000,1000 minimum=500

SEE ALSO

        v.random, v.univar

AUTHOR

       James Darrell McCauley
       when he was at: Agricultural Engineering Purdue University

       Random number generators originally written in FORTRAN by Wes Peterson and translated to C using f2c.

SOURCE CODE

       Available at: v.perturb source code (history)

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       © 2003-2019 GRASS Development Team, GRASS GIS 7.8.2 Reference Manual