## 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*

*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.

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.

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.*
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.*
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

*
v.random,
v.univar
*
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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GRASS Development Team,
GRASS GIS 8.0.dev Reference Manual