GRASS GIS manual: v.net.flow

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NAME

v.net.flow - Computes the maximum flow between two sets of nodes in the network.

KEYWORDS

vector, network, flow

SYNOPSIS

v.net.flow
v.net.flow help
v.net.flow input=name [layer=integer] output=name cut=name [afcolumn=name] [abcolumn=name] [source_layer=integer] [source_cats=range] [source_where=sql_query] [sink_layer=integer] [sink_cats=range] [sink_where=sql_query] [--overwrite] [--verbose] [--quiet]

Flags:

--overwrite: Allow output files to overwrite existing files
--verbose: Verbose module output
--quiet: Quiet module output

Parameters:

input=name: Name of input vector map
layer=integer: Layer number; A single vector map can be connected to multiple database tables. This number determines which table to use.; Default: 1
output=name: Name for output vector map
cut=name: Name for output vector map containing a minimum cut
afcolumn=name: Name of arc forward/both direction(s) capacity column
abcolumn=name: Name of arc backward direction capacity column
source_layer=integer: Source layer number or name; A single vector map can be connected to multiple database tables. This number determines which table to use.; Default: 1
source_cats=range: Source category values; Example: 1,3,7-9,13
source_where=sql_query: Source WHERE conditions of SQL statement without 'where' keyword; Example: income < 1000 and inhab >= 10000
sink_layer=integer: Sink layer number or name; A single vector map can be connected to multiple database tables. This number determines which table to use.; Default: 1
sink_cats=range: Sink category values; Example: 1,3,7-9,13
sink_where=sql_query: Sink WHERE conditions of SQL statement without 'where' keyword; Example: income < 1000 and inhab >= 10000

DESCRIPTION

v.net.flow computes the maximum flow and minimum cut between two sets of nodes.

NOTES

The two sets of nodes are called sources and sink and v.net.flow finds the maximimum flow from the former to the latter ones. Edge capacities can be specified by afcolumn for forward direction and abcolumn for backward direction. If the latter parameter is ommited then the same capacity is used in either direction. The sets are given by the respective cats, layer and where parameters. Maximum flow corresponds to the maximum amount of water possibly flowing through the network preserving the capacity constraints and minimum cut to the set of edges of minimum total capacity completely separating sources from sinks. The cut produced by this module corresponds to the first fully saturated edges from sources to sinks. An attribute table containing the flow information is linked to the output map. The table consists of two columns: cat and flow and stores the flow along each line. Negative flow means that "water" is flowing in the backward direction. Cut map contains the edges in the minimum cut.
A famous result says that the total amount of water flowing is equal to the minimum cut.

EXAMPLES

Find maximum flow from factories to stores using SPEED for the capacities.

v.net.flow input=roads output=roads_flow cut=roads_cut afcolumn=SPEED \
           source_where="type=factory" sink_where="type=store"

If all the capacties are one then the minimum cut corresponds to the minimum number of edges separating sources from sinks.

v.net.flow input=network output=flow cut=cut afcolumn=ones \
           source_cats=1-10 sink_cats=100-100

AUTHORS

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

Last changed: $Date: 2013-05-23 13:00:25 -0700 (Thu, 23 May 2013) $

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