.TH v.net.components 1grass "" "GRASS 7.8.5" "GRASS GIS User's Manual"
.SH NAME
\fI\fBv.net.components\fR\fR  \- Computes strongly and weakly connected components in the network.
.SH KEYWORDS
vector, network, components
.SH SYNOPSIS
\fBv.net.components\fR
.br
\fBv.net.components \-\-help\fR
.br
\fBv.net.components\fR [\-\fBa\fR] \fBinput\fR=\fIname\fR  [\fBarc_layer\fR=\fIstring\fR]   [\fBnode_layer\fR=\fIstring\fR]   [\fBarc_column\fR=\fIname\fR]   [\fBarc_backward_column\fR=\fIname\fR]   [\fBnode_column\fR=\fIstring\fR]  \fBoutput\fR=\fIname\fR \fBmethod\fR=\fIstring\fR  [\-\-\fBoverwrite\fR]  [\-\-\fBhelp\fR]  [\-\-\fBverbose\fR]  [\-\-\fBquiet\fR]  [\-\-\fBui\fR]
.SS Flags:
.IP "\fB\-a\fR" 4m
.br
Add points on nodes
.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 map
.br
Or data source for direct OGR access
.IP "\fBarc_layer\fR=\fIstring\fR" 4m
.br
Arc layer
.br
Vector features can have category values in different layers. This number determines which layer to use. When used with direct OGR access this is the layer name.
.br
Default: \fI1\fR
.IP "\fBnode_layer\fR=\fIstring\fR" 4m
.br
Node layer
.br
Vector features can have category values in different layers. This number determines which layer to use. When used with direct OGR access this is the layer name.
.br
Default: \fI2\fR
.IP "\fBarc_column\fR=\fIname\fR" 4m
.br
Arc forward/both direction(s) cost column (number)
.IP "\fBarc_backward_column\fR=\fIname\fR" 4m
.br
Arc backward direction cost column (number)
.IP "\fBnode_column\fR=\fIstring\fR" 4m
.br
Node cost column (number)
.IP "\fBoutput\fR=\fIname\fR \fB[required]\fR" 4m
.br
Name for output vector map
.IP "\fBmethod\fR=\fIstring\fR \fB[required]\fR" 4m
.br
Type of components
.br
Options: \fIweak, strong\fR
.br
\fBweak\fR: Weakly connected components
.br
\fBstrong\fR: Strongly connected components
.SH DESCRIPTION
\fIv.net.components\fR computes the weakly and strongly connected
components in a network.
.SH NOTES
Two nodes, \fIu\fR and \fIv\fR are in the same strongly connected
component if there are directed paths from \fIu\fR to \fIv\fR and
from \fIv\fR to \fIu\fR. The nodes are in the same weakly
connected component if, ignoring edge directions, there is a path
between them.
.PP
The type of components is specified by \fBmethod\fR parameter.
\fIv.net.components\fR creates a table and links it to layer 1. This
table contains only two integer columns: \fIcat\fR and
\fIcomp\fR. If a point or both endpoints of a line belong to the
same component then the point/line is written to the output map and
appropriate information is stored in the table. If \fB\-a\fR flag is
set then new points are added on the nodes without points. These points
have category numbers larger than any category used in the input map.
.PP
One\-way roads can be defined by assigning a cost of \-1 to the
appropriate cost column (\fBarc_column\fR or
\fBarc_backward_column\fR). This affects only strongly connected
components. Network nodes can be closed by assigning a cost of \-1 to
the node cost column. All nodes with a cost < 0 can not be traversed
and are end points, while all nodes with a cost ≥ 0 can be traversed.
This affects both weakly and strongly connected components.
.SH EXAMPLES
Any road network should form a single strongly connected component.
Otherwise, it is impossible to travel between some places.
.br
.nf
\fC
v.net.components input=roads output=roads_components method=strong
\fR
.fi
.SH SEE ALSO
\fI
v.net,
v.category,
\fR
.SH AUTHORS
Daniel Bundala, Google Summer of Code 2009, Student
.br
Wolf Bergenheim, Mentor
.br
Markus Metz
.SH SOURCE CODE
.PP
Available at: v.net.components source code (history)
.PP
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.PP
© 2003\-2020
GRASS Development Team,
GRASS GIS 7.8.5 Reference Manual