1v.voronoi(1)                  Grass User's Manual                 v.voronoi(1)
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NAME

6       v.voronoi   -  Creates  a Voronoi diagram constrained to the extents of
7       the current region from an input vector map containing points  or  cen‐
8       troids.
9

KEYWORDS

11       vector, geometry, triangulation, skeleton
12

SYNOPSIS

14       v.voronoi
15       v.voronoi --help
16       v.voronoi  [-aslt]  input=name   [layer=string]   output=name  [smooth‐
17       ness=float]    [thin=float]    [--overwrite]    [--help]    [--verbose]
18       [--quiet]  [--ui]
19
20   Flags:
21       -a
22           Create Voronoi diagram for input areas
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24       -s
25           Extract skeletons for input areas
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27       -l
28           Output tessellation as a graph (lines), not areas
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30       -t
31           Do not create attribute table
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33       --overwrite
34           Allow output files to overwrite existing files
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36       --help
37           Print usage summary
38
39       --verbose
40           Verbose module output
41
42       --quiet
43           Quiet module output
44
45       --ui
46           Force launching GUI dialog
47
48   Parameters:
49       input=name [required]
50           Name of input vector map
51           Or data source for direct OGR access
52
53       layer=string
54           Layer number or name (’-1’ for all layers)
55           A  single  vector map can be connected to multiple database tables.
56           This number determines which table to use. When  used  with  direct
57           OGR access this is the layer name.
58           Default: -1
59
60       output=name [required]
61           Name for output vector map
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63       smoothness=float
64           Factor for output smoothness
65           Applies to input areas only. Smaller values produce smoother output
66           but can cause numerical instability.
67           Default: 0.25
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69       thin=float
70           Maximum dangle length of skeletons
71           Applies only to skeleton extraction. Default = -1 will extract  the
72           center line.
73           Default: -1
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DESCRIPTION

76       v.voronoi  creates a Voronoi diagram (Thiessen polygons) from points or
77       centroids.
78
79       The bounds of the output map are limited by  the  current  region  (see
80       g.region).
81
82       The -a flag can be used to create a Voronoi diagram for areas.
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84       The  -s  flag can be used to extract the center line of areas or skele‐
85       tons of areas with thin >= 0. Smaller values for the thin  option  will
86       preserve  more detail, while negative values will extract only the cen‐
87       ter line.
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NOTES

90       v.voronoi suffers from numerical  instability,  results  can  sometimes
91       contain  many  artefacts.  When  creating Voronoi diagrams for areas or
92       skeletons for areas, it is highly recommended  to  simplify  the  areas
93       first with v.generalize.
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95       Voronoi  diagrams may be used for nearest-neighbor flood filling.  Give
96       the centroids attributes (start with v.db.addcolumn),  then  optionally
97       convert the result to a raster map with v.to.rast.
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99       The  extraction  of  skeletons  and  center lines with the -s flag is a
100       brute force approach. Faster and more accurate  algorithms  to  extract
101       skeletons  from  areas  exist but are not yet implemented. In the mean‐
102       time, skeletons and center  lines  can  be  simplified  with  the  Dou‐
103       glas-Peucker algorithm: v.generalize method=douglas.
104

EXAMPLE

106   Voronoi diagram for points
107       This example uses the hospitals in the North Carolina dataset.
108       g.region -p raster=elev_state_500m
109       v.voronoi input=hospitals output=hospitals_voronoi
110       Result:
111       Voronoi diagram for hospitals in North Carolina
112
113   Voronoi diagram for areas
114       This example uses urban areas in the North Carolina dataset.
115       g.region -p n=162500 s=80000 w=727000 e=846000 res=500
116       v.voronoi input=urbanarea output=urbanarea_voronoi -a
117       Result:
118       Voronoi diagram for urban areas in North Carolina
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120   Skeletons and center lines of areas
121       This example uses urban areas in the North Carolina dataset.
122       g.region -p n=161000 s=135500 w=768500 e=805500 res=500
123       v.voronoi input=urbanarea output=urbanarea_centerline -s
124       v.voronoi input=urbanarea output=urbanarea_skeleton -s thin=2000
125       Result:
126       Skeleton (blue) and center line (red) for urban areas in North Carolina
127

REFERENCES

129       Steve J. Fortune,  (1987).  A Sweepline Algorithm for Voronoi Diagrams,
130       Algorithmica 2, 153-174 (DOI).
131

SEE ALSO

133        g.region, v.delaunay, v.hull
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AUTHORS

136       James Darrell McCauley, Purdue University
137       GRASS 5 update, improvements: Andrea Aime, Modena, Italy
138       GRASS 5.7 update: Radim Blazek
139       Markus Metz
140

SOURCE CODE

142       Available at: v.voronoi source code (history)
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144       Main index | Vector index | Topics index | Keywords index  |  Graphical
145       index | Full index
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147       © 2003-2019 GRASS Development Team, GRASS GIS 7.8.2 Reference Manual
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151GRASS 7.8.2                                                       v.voronoi(1)
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