v.net.components(1)

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 access 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 access 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.components 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 appropriate 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

Last changed: $Date$

SOURCE CODE

Available at: v.net.components source code (history)

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