1v.random(1) Grass User's Manual v.random(1)
2
6 v.random - Generates random 2D/3D vector points.
7
9 vector, sampling, statistics, random, point pattern, stratified random
10 sampling, level1
11
13 v.random
14 v.random --help
15 v.random [-zab] output=name npoints=integer [restrict=name]
16 [layer=string] [cats=range] [where=sql_query] [zmin=float]
17 [zmax=float] [seed=integer] [column=name] [column_type=string]
18 [--overwrite] [--help] [--verbose] [--quiet] [--ui]
19 Flags:
21 -z
22 Create 3D output
23 -a
25 Generate n points for each individual area (requires restrict
26 parameter)
27 -b
29 Do not build topology
30 Advantageous when handling a large number of points
31 --overwrite
33 Allow output files to overwrite existing files
34 --help
36 Print usage summary
37 --verbose
39 Verbose module output
40 --quiet
42 Quiet module output
43 --ui
45 Force launching GUI dialog
46 Parameters:
48 output=name [required]
49 Name for output vector map
50 npoints=integer [required]
52 Number of points to be created
53 restrict=name
55 Name of input vector map
56 Restrict points to areas in input vector
57 layer=string
59 Layer number or name (’-1’ for all layers)
60 A single vector map can be connected to multiple database tables.
61 This number determines which table to use. When used with direct
62 OGR access this is the layer name.
63 Default: -1
64 cats=range
66 Category values
67 Example: 1,3,7-9,13
68 where=sql_query
70 WHERE conditions of SQL statement without ’where’ keyword
71 Example: income < 1000 and population >= 10000
72 zmin=float
74 Minimum z height (needs -z flag or column name)
75 Default: 0.0
76 zmax=float
78 Maximum z height (needs -z flag or column name)
79 Default: 0.0
80 seed=integer
82 The seed to initialize the random generator. If not set the process
83 ID is used
84 column=name
86 Name of column for z values
87 Writes z values to column
88 column_type=string
90 Type of column for z values
91 Options: integer, double precision
92 Default: double precision
93
95 v.random randomly generates vector points within the current region
96 using the selected random number generator.
97 v.random can generate also 3D vector points or write random value to
99 attribute table. Point height range or attribute value range is con‐
100 trolled by specifying zmin and zmax options. Both z values are
101 included in range (zmin <= z <= zmax). Generated random attribute value
102 type can be controlled by column_type. Use integer column type for
103 integers and double precision for floating point numbers. Integer val‐
104 ues are calculated by rounding random floating point number.
105 To produce repeatable results a random seed can be set using the option
107 seed.
108 Restriction to vector areas
110 If an restrict vector map with areas is specified, the location of ran‐
111 dom points is restricted to the selected areas. By default, the
112 requested number of points are distributed across all areas.
113 If the -a flag is given, the requested number of points is generated
115 for each individual area. For example, if 20 points should be generated
116 and the input map has 100 individual areas, 2000 points will be gener‐
117 ated in total.
118
120 All examples are based on the North Carolina sample dataset.
121 Generating random points in 2D
123 Generate 20 random points with binary attributes (only 0 or 1):
124 v.random output=binary_random npoints=20 zmin=0 zmax=1 column=’binary’
125 v.db.select binary_random
126 cat|binary
127 1|0.63495
128 2|0.233421
129 3|0.489302
130 4|0.748264
131 5|0.505556
132 6|0.32975
133 [...]
134 v.univar -d binary_random
135 Calculating geometric distances between 20 primitives...
136 [...]
137 minimum: 148.515
138 maximum: 16572.8
139 [...]
140 Generating random points in 2D with binary attributes
142 Generate 20 random points with binary attributes (only 0 or 1):
143 v.random output=binary_random npoints=20 zmin=0 zmax=1 column=’binary’ column_type=integer
144 v.db.select binary_random
145 cat|binary
146 1|0
147 2|0
148 3|0
149 4|0
150 5|1
151 6|0
152 [...]
153 Generating random points in 3D
155 Generate 20 random 3D points using a specific random seed:
156 v.random seed=52 output=height_random npoints=40 zmin=110 zmax=170 -z
157 v.univar -d height_random
158 Calculating geometric distances between 40 primitives...
159 [...]
160 minimum: 334.889
161 maximum: 18351.9
162 range: 18017
163 sum: 5.38425e+06
164 mean: 7266.2
165 mean of absolute values: 7266.2
166 population standard deviation: 3563.95
167 [...]
168 skewness: 0.34703
169 Random points with different X, Y, and Z coordinates
171 Generating random points in selected polygons
173 Generate 3 random points only in selected polygons ("RALEIGH" related
174 ZIP code areas):
175 v.random restrict=zipcodes_wake output=zipcodes_local_random_n3 npoints=3 where="ZIPNAME = ’RALEIGH’" -a
176 # visualization
177 d.mon wx0
178 d.vect zipcodes_wake
179 d.vect zipcodes_wake fcolor=yellow where="ZIPNAME = ’RALEIGH’"
180 d.vect zipcodes_local_random_n3 color=red icon=basic/circle
181 Fixed number of random points generated in selected polygons
182 Generating random adjacent polygons
184 To generate random adjacent polygons, first the centroids are generated
185 as points, then a triangulation is run (North Carolina sample dataset:
186 g.region vector=nc_state
187 v.random output=randpoints6k npoints=6000
188 v.voronoi input=randpoints6k output=randareas6k
189 v.info -t randareas6k
190 v.category randareas6k option=print
191 # plot vector polygons
192 d.mon wx0
193 d.vect randareas6k -c
194 Random adjacent polygons from random points (here: used as centroids)
196 To eventually obtain isolated polygons, selected polygons can be
198 extracted with v.extract.
199 These vector polygons can also be rasterized:
201 # rasterize polygons
202 # note: rastermaps must result in at least 6k pixel in this example
203 g.region vector=nc_state res=500 -p -a
204 v.to.rast randareas6k out=randareas6k use=cat
205 r.colors randareas6k color=random
206 d.rast randareas6k
207 Random sampling from raster map
209 Generate 20 random samples from a raster map:
210 g.region -p raster=elevation
211 v.random output=random_samples npoints=20
212 v.db.addtable map=random_samples columns=’cat INTEGER, sample DOUBLE PRECISION’
213 v.what.rast map=random_samples raster=elevation column=sample
214 v.db.select random_samples
215 cat|sample
216 1|103.9935
217 2|129.1266
218 3|96.01388
219 [...]
220 Random sampling from vector map
222 Generate 20 random points and sample attribute data from geology (vec‐
223 tor) map:
224 g.region -p vector=geology
225 v.random output=random_samples npoints=20
226 v.db.addtable map=random_samples columns=’cat integer, geology varchar(100)’
227 v.what.vect map=random_samples column=geology query_map=geology query_layer=1 query_column=GEO_NAME
228 v.db.select random_samples
229 cat|geology
230 1|PzZm
231 2|
232 3|Zatm
233 [...]
234 Stratified random sampling: Random sampling from vector map by attribute
236 Generate 20 random points restricted to forested areas:
237 g.region -p raster=landclass96
238 r.to.vect -v input=landclass96 output=landclass96 type=area
239 v.random restrict=landclass96 output=random_samples npoints=20 where="label = ’forest’" layer=1
240 Random points only sampled in forested areas (stratified random sam‐
242 pling)
243 Stratified random sampling: Random sampling from vector map with spatial
245 constraints
246 Generating n points for each individual area: in this example two ran‐
247 dom points in each water body:
248 g.region -p raster=landclass96
249 r.to.vect -v input=landclass96 output=landclass96 type=area
250 v.random restrict=landclass96 output=random_samples npoints=2 where="label = ’water’" layer=1 -a
251 Two random points sampled in each individual water body (stratified
253 random sampling)
254
256 g.region, r.random, v.db.addtable, v.perturb, v.sample, v.univar,
257 v.what.rast, v.what.vect
258 SQL support in GRASS GIS
260
262 James Darrell McCauley <darrell@mccauley-usa.com>,
263 when he was at: Agricultural Engineering Purdue University
264 Last changed: $Date: 2018-04-06 19:51:18 +0200 (Fri, 06 Apr 2018) $
266
268 Available at: v.random source code (history)
269 Main index | Vector index | Topics index | Keywords index | Graphical
271 index | Full index
272 © 2003-2019 GRASS Development Team, GRASS GIS 7.4.4 Reference Manual
274GRASS 7.4.4 v.random(1)