.TH v.voronoi 1grass "" "GRASS 7.2.0" "Grass User's Manual"
.SH NAME
\fI\fBv.voronoi\fR\fR  \- Creates a Voronoi diagram in current region from an input vector map containing points or centroids.
.SH KEYWORDS
vector, geometry, triangulation, skeleton
.SH SYNOPSIS
\fBv.voronoi\fR
.br
\fBv.voronoi \-\-help\fR
.br
\fBv.voronoi\fR [\-\fBaslt\fR] \fBinput\fR=\fIname\fR  [\fBlayer\fR=\fIstring\fR]  \fBoutput\fR=\fIname\fR  [\fBsmoothness\fR=\fIfloat\fR]   [\fBthin\fR=\fIfloat\fR]   [\-\-\fBoverwrite\fR]  [\-\-\fBhelp\fR]  [\-\-\fBverbose\fR]  [\-\-\fBquiet\fR]  [\-\-\fBui\fR]
.SS Flags:
.IP "\fB\-a\fR" 4m
.br
Create Voronoi diagram for input areas
.IP "\fB\-s\fR" 4m
.br
Extract skeletons for input areas
.IP "\fB\-l\fR" 4m
.br
Output tessellation as a graph (lines), not areas
.IP "\fB\-t\fR" 4m
.br
Do not create attribute table
.IP "\fB\-\-overwrite\fR" 4m
.br
Allow output files to overwrite existing files
.IP "\fB\-\-help\fR" 4m
.br
Print usage summary
.IP "\fB\-\-verbose\fR" 4m
.br
Verbose module output
.IP "\fB\-\-quiet\fR" 4m
.br
Quiet module output
.IP "\fB\-\-ui\fR" 4m
.br
Force launching GUI dialog
.SS Parameters:
.IP "\fBinput\fR=\fIname\fR \fB[required]\fR" 4m
.br
Name of input vector point map
.br
Or data source for direct OGR access
.IP "\fBlayer\fR=\fIstring\fR" 4m
.br
Layer number or name (\(cq\-1\(cq for all layers)
.br
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.
.br
Default: \fI\-1\fR
.IP "\fBoutput\fR=\fIname\fR \fB[required]\fR" 4m
.br
Name for output vector map
.IP "\fBsmoothness\fR=\fIfloat\fR" 4m
.br
Factor for output smoothness
.br
Applies to input areas only. Smaller values produce smoother output but can cause numerical instability.
.br
Default: \fI0.25\fR
.IP "\fBthin\fR=\fIfloat\fR" 4m
.br
Maximum dangle length of skeletons
.br
Applies only to skeleton extraction. Default = \-1 will extract the center line.
.br
Default: \fI\-1\fR
.SH DESCRIPTION
\fIv.voronoi\fR creates a Voronoi diagram (Thiessen polygons) from
points or centroids.
.PP
The bounds of the output map are limited by the current region
(see \fIg.region\fR).
.PP
The \fI\-a\fR flag can be used to create a Voronoi diagram for areas.
.PP
The \fI\-s\fR flag can be used to extract the center line of areas or
skeletons of areas with \fIthin\fR >= 0. Smaller values for the
\fIthin\fR option will preserve more detail, while negative values
will extract only the center line.
.SH NOTES
Voronoi diagrams may be used for nearest\-neighbor flood filling.
Give the centroids attributes (start with
\fIv.db.addcolumn\fR),
then optionally convert the result to a raster map with
\fIv.to.rast\fR.
.PP
The extraction of skeletons and center lines with the \fI\-s\fR flag
is a brute force approach. Faster and more accurate algorithms to
extract skeletons from areas exist but are not yet implemented. In the
meantime, skeletons and center lines can be simplified with the
Douglas\-Peucker algorithm:
\fIv.generalize method=douglas\fR.
.SH EXAMPLE
.SS Voronoi diagram for points
This example uses the hospitals in the North Carolina dataset.
.br
.nf
\fC
g.region \-p raster=elev_state_500m
v.voronoi input=hospitals output=hospitals_voronoi
\fR
.fi
Result:
.br
\fIVoronoi diagram for hospitals in North Carolina\fR
.SS Voronoi diagram for areas
This example uses urban areas in the North Carolina dataset.
.br
.nf
\fC
g.region \-p n=162500 s=80000 w=727000 e=846000 res=500
v.voronoi input=urbanarea output=urbanarea_voronoi \-a
\fR
.fi
Result:
.br
\fIVoronoi diagram for urban areas in North Carolina\fR
.SS Skeletons and center lines of areas
This example uses urban areas in the North Carolina dataset.
.br
.nf
\fC
g.region \-p n=161000 s=135500 w=768500 e=805500 res=500
v.voronoi input=urbanarea output=urbanarea_centerline \-s
v.voronoi input=urbanarea output=urbanarea_skeleton \-s thin=2000
\fR
.fi
Result:
.br
\fISkeleton (blue) and center line (red) for urban areas in North Carolina\fR
.SH REFERENCES
\fISteve J. Fortune,  (1987).  A Sweepline Algorithm for
Voronoi Diagrams, Algorithmica 2, 153\-174
(DOI).\fR
.SH SEE ALSO
\fI
g.region,
v.delaunay,
v.hull
\fR
.SH AUTHORS
James Darrell McCauley, Purdue University
.br
GRASS 5 update, improvements: Andrea Aime, Modena, Italy
.br
GRASS 5.7 update: Radim Blazek
.br
Markus Metz
.PP
\fILast changed: $Date: 2015\-06\-08 09:20:07 +0200 (Mon, 08 Jun 2015) $\fR
.SH SOURCE CODE
.PP
Available at: v.voronoi source code (history)
.PP
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.PP
© 2003\-2016
GRASS Development Team,
GRASS GIS 7.2.0 Reference Manual