# v.perturb.1grass man page

**v.perturb** — Random location perturbations of vector points.

## Keywords

vector, geometry, statistics, random, point pattern

## 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
**--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.

## 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*.

*Last changed: $Date: 2011-11-08 13:24:20 -0800 (Tue, 08 Nov 2011) $*

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