Provided by: grass-doc_7.6.1-3_all

**NAME**

v.perturb- Random location perturbations of vector points.

**KEYWORDS**

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

**SYNOPSIS**

v.perturbv.perturb--helpv.perturb[-b]input=name[layer=string]output=name[distribution=string]parameters=float[,float,...] [minimum=float] [seed=integer] [--overwrite] [--help] [--verbose] [--quiet] [--ui]Flags:-bDo not build topology Advantageous when handling a large number of points--overwriteAllow output files to overwrite existing files--helpPrint usage summary--verboseVerbose module output--quietQuiet module output--uiForce launching GUI dialogParameters:input=name[required]Name of input vector map Or data source for direct OGR accesslayer=stringLayer 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:-1output=name[required]Name for output vector mapdistribution=stringDistribution of perturbation Options:uniform,normalDefault:uniformparameters=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=floatMinimum deviation in map units Default:0.0seed=integerSeed for random number generation Default:0

**DESCRIPTION**

v.perturbreads a vector map of points and writes the same points butperturbsthe 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 associatedparameteris 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, theminimumparameter 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,uniformlydistributedselectionTo 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:Mapshowingtheactualcommunitycollegepointsanduniformlyrandomchosenpoints.NormaldistributedselectionFor 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=5000,2000Figure:Mapshowingtheactualcommunitycollegepointsandnormallyrandomchosenandcoloredpoints.Noticethateachpointisclosertotheoriginalpoint.NormaldistributedselectionwithaminimumvalueIn 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 usingf2c.Lastchanged:$Date:2018-01-0716:11:10+0100(Sun,07Jan2018)$

**SOURCE** **CODE**

Available at: v.perturb source code (history) Main index | Vector index | Topics index | Keywords index | Graphical index | Full index © 2003-2019 GRASS Development Team, GRASS GIS 7.6.1 Reference Manual