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

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