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

AUTHORS

Daniel Bundala, Google Summer of Code 2009, Student
Wolf Bergenheim, Mentor
Markus Metz

SOURCE CODE

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