v.net.components(1grass) GRASS GIS User's Manual v.net.components(1grass)
NAME
v.net.components - Computes strongly and weakly connected components
in the network.
KEYWORDS
vector, network, components
SYNOPSIS
v.net.components
v.net.components --help
v.net.components [-a] input=name [arc_layer=string]
[node_layer=string] [arc_column=name] [arc_backward_column=name]
[node_column=string] output=name method=string [--overwrite]
[--help] [--verbose] [--quiet] [--ui]
Flags:
-a
Add points on nodes
--overwrite
Allow output files to overwrite existing files
--help
Print usage summary
--verbose
Verbose module output
--quiet
Quiet module output
--ui
Force launching GUI dialog
Parameters:
input=name [required]
Name of input vector map
Or data source for direct OGR access
arc_layer=string
Arc layer
Vector features can have category values in different layers. This
number determines which layer to use. When used with direct OGR ac-
cess this is the layer name.
Default: 1
node_layer=string
Node layer
Vector features can have category values in different layers. This
number determines which layer to use. When used with direct OGR ac-
cess this is the layer name.
Default: 2
arc_column=name
Arc forward/both direction(s) cost column (number)
arc_backward_column=name
Arc backward direction cost column (number)
node_column=string
Node cost column (number)
output=name [required]
Name for output vector map
method=string [required]
Type of components
Options: weak, strong
weak: Weakly connected components
strong: Strongly connected components
DESCRIPTION
v.net.components computes the weakly and strongly connected components
in a network.
NOTES
Two nodes, u and v are in the same strongly connected component if
there are directed paths from u to v and from v to u. The nodes are in
the same weakly connected component if, ignoring edge directions, there
is a path between them.
The type of components is specified by method parameter. v.net.compo-
nents creates a table and links it to layer 1. This table contains only
two integer columns: cat and comp. 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 -a
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.
One-way roads can be defined by assigning a cost of -1 to the appropri-
ate cost column (arc_column or arc_backward_column). 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.
EXAMPLES
Any road network should form a single strongly connected component.
Otherwise, it is impossible to travel between some places.
v.net.components input=roads output=roads_components method=strong
SEE ALSO
v.net, v.category,
AUTHORS
Daniel Bundala, Google Summer of Code 2009, Student
Wolf Bergenheim, Mentor
Markus Metz
SOURCE CODE
Available at: v.net.components source code (history)
Accessed: unknown
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