v.voronoi(1grass)

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.
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KEYWORDS

11       vector, geometry, triangulation, skeleton
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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]
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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
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39       --verbose
40           Verbose module output
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42       --quiet
43           Quiet module output
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45       --ui
46           Force launching GUI dialog
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48   Parameters:
49       input=name [required]
50           Name of input vector map
51           Or data source for direct OGR access
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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
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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.
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79       The bounds of the output map are limited by  the  current  region  (see
80       g.region).
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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       Voronoi diagrams may be used for nearest-neighbor flood filling.   Give
91       the  centroids  attributes (start with v.db.addcolumn), then optionally
92       convert the result to a raster map with v.to.rast.
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94       The extraction of skeletons and center lines with  the  -s  flag  is  a
95       brute  force  approach.  Faster and more accurate algorithms to extract
96       skeletons from areas exist but are not yet implemented.  In  the  mean‐
97       time,  skeletons  and  center  lines  can  be  simplified with the Dou‐
98       glas-Peucker algorithm: v.generalize method=douglas.
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EXAMPLE

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

124       Steve J. Fortune,  [4m(1987).  A Sweepline Algorithm for Voronoi Diagrams,
125       Algorithmica 2, 153-174 (DOI).
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AUTHORS

131       James Darrell McCauley, Purdue University
132       GRASS 5 update, improvements: Andrea Aime, Modena, Italy
133       GRASS 5.7 update: Radim Blazek
134       Markus Metz
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136       Last changed: $Date: 2015-06-08 09:20:07 +0200 (Mon, 08 Jun 2015) $
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SOURCE CODE

139       Available at: v.voronoi source code (history)
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141       Main  index  | Vector index | Topics index | Keywords index | Graphical
142       index | Full index
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144       © 2003-2019 GRASS Development Team, GRASS GIS 7.6.0 Reference Manual
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148GRASS 7.6.0                                                       v.voronoi(1)