1v.perturb(1) Grass User's Manual v.perturb(1)
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6 v.perturb - Random location perturbations of vector points.
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9 vector, geometry, statistics, random, point pattern, level1
10
12 v.perturb
13 v.perturb --help
14 v.perturb [-b] input=name [layer=string] output=name [distribu‐
15 tion=string] parameters=float[,float,...] [minimum=float]
16 [seed=integer] [--overwrite] [--help] [--verbose] [--quiet]
17 [--ui]
18 Flags:
20 -b
21 Do not build topology
22 Advantageous when handling a large number of points
23 --overwrite
25 Allow output files to overwrite existing files
26 --help
28 Print usage summary
29 --verbose
31 Verbose module output
32 --quiet
34 Quiet module output
35 --ui
37 Force launching GUI dialog
38 Parameters:
40 input=name [required]
41 Name of input vector map
42 Or data source for direct OGR access
43 layer=string
45 Layer number or name (’-1’ for all layers)
46 A single vector map can be connected to multiple database tables.
47 This number determines which table to use. When used with direct
48 OGR access this is the layer name.
49 Default: -1
50 output=name [required]
52 Name for output vector map
53 distribution=string
55 Distribution of perturbation
56 Options: uniform, normal
57 Default: uniform
58 parameters=float[,float,...]Â [required]
60 Parameter(s) of distribution
61 If the distribution is uniform, only one parameter, the maximum, is
62 needed. For a normal distribution, two parameters, the mean and
63 standard deviation, are required.
64 minimum=float
66 Minimum deviation in map units
67 Default: 0.0
68 seed=integer
70 Seed for random number generation
71 Default: 0
72
74 v.perturb reads a vector map of points and writes the same points but
75 perturbs the eastings and northings by adding either a uniform or nor‐
76 mal delta value. Perturbation means that a variating spatial deviation
77 is added to the coordinates.
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80 The uniform distribution is always centered about zero. The associated
81 parameter is constrained to be positive and specifies the maximum of
82 the distribution; the minimum is the negation of that parameter. Do
83 perturb into a ring around the center, the minimum parameter can be
84 used.
85 Usually, the mean (first parameter) of the normal distribution is zero
87 (i.e., the distribution is centered at zero). The standard deviation
88 (second parameter) is naturally constrained to be positive.
89 Output vector points are not guaranteed to be contained within the cur‐
91 rent geographic region.
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94 Random, uniformly distributed selection
95 To create a random, uniformly distributed selection of possible new
96 points with a radius of 100,000 map units, use the following command:
97 v.perturb input=comm_colleges output=uniform_perturb parameters=100000
98 Your map should look similar to this figure:
99 Figure: Map showing the actual community college points and uniformly
100 random chosen points.
101 Normal distributed selection
103 For a normal distribution with a mean of 5000 and standard deviation of
104 2000, use the following command:
105 v.perturb input=comm_colleges output=normal_perturb distribution=normal parameters=5000,2000
106 Figure: Map showing the actual community college points and normally
107 random chosen and colored points. Notice that each point is closer to
108 the original point.
109 Normal distributed selection with a minimum value
111 In order to include a minimum value of 500, use the following command:
112 v.perturb input=comm_colleges output=min_perturb distribution=normal parameters=100000,1000 minimum=500
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115 v.random, v.univar
116
118 James Darrell McCauley
119 when he was at: Agricultural Engineering Purdue University
120 Random number generators originally written in FORTRAN by Wes Peterson
122 and translated to C using f2c.
123
125 Available at: v.perturb source code (history)
126 Main index | Vector index | Topics index | Keywords index | Graphical
128 index | Full index
129 © 2003-2019 GRASS Development Team, GRASS GIS 7.8.2 Reference Manual
131GRASS 7.8.2 v.perturb(1)