Ubuntu Manpage: v.net - Performs network maintenance.

NAME

       v.net  - Performs network maintenance.

KEYWORDS

       vector, networking, maintenance

SYNOPSIS

       v.net
       v.net help
       v.net    [-c]   input=name    [points=name]     [output=name]     [operation=string]     [alayer=integer]
       [nlayer=integer]   [thresh=float]   [--overwrite]  [--verbose]  [--quiet]

   Flags:
       -c
           Assign unique categories to new points
           For operation 'nodes'

       --overwrite
           Allow output files to overwrite existing files

       --verbose
           Verbose module output

       --quiet
           Quiet module output

   Parameters:
       input=name
           Name of input vector map

       points=name
           Name of input point vector map
           Required for operation 'connect'

       output=name
           Name for output vector map

       operation=string
           Operation to be performed
           Options: nodes,connect,report,nreport
           Default: nodes
           nodes: new point is placed on each node (line end) if doesn't exist
           connect: connect still unconnected points to vector network by inserting new line(s)
           report: print to standard output {line_category start_point_category end_point_category}
           nreport: print to standard output {point_category line_category[,line_category...]}

       alayer=integer
           Arc layer
           A single vector map can be connected to multiple database tables. This number determines which  table
           to use.
           Default: 1

       nlayer=integer
           Node layer
           A  single vector map can be connected to multiple database tables. This number determines which table
           to use.
           Default: 2

       thresh=float
           Threshold
           Required for operation 'connect'. Connect points in given threshold.

DESCRIPTION

v.net is used for network preparation and maintenance. Its main use is to create a vector network from
vector lines (arcs ) and points (nodes) by creating nodes from intersections in a map of vector lines
(node operator), by connecting a vector lines map with a points map (connect operator), and by creating
new lines between pairs of vector points (arcs operator).

A GIS network consists of topologically correct lines (arcs). That is, the lines must be connected by
shared vertices where real connections exist. In GRASS GIS you also can add nodes to the network. These
are specially designated vertices used for analyzing network properties or computing cost/distance
measures. That is, not all vertices are treated as nodes by default. Only v.net.path can use a network
without nodes, they are required for all the other network modules. In GRASS, network arcs are stored
in one data layer (normally layer 1) and nodes are stored in a different data layer (normally layer 2).

v.net offers two ways to add nodes to a network of arcs:

1 Use the connect operation to create nodes from a vector points file and add these nodes to an
existing vector network of arcs (i.e., lines/boundaries). This is useful when the goal is to
analyze a set of places (points) in relation to a network--for example travel costs between
places. Only points within the thresh (threshold) distance to a line/boundary will be connected
as network nodes.

2 Create nodes and arcs from a vector line/boundary file using the node operation. This is useful if
you are mostly interested in the network itself and thus you can use intersections of the network
as start and end points. Nodes will be created at all intersections of two or more lines. For an
arc that consists of several segments connected by vertices (the typical case), only the starting
and ending vertices are treated as network nodes.

While the arcs created with v.net will retain any attribute information associated with the input vector
line/boundary file in data layer 1, nodes created and stored in data layer 2 will not have any associated
attribute information.

For nodes created using the connect operation (method 1 above), the nodes can be reconnected to the
attribute table of the input vector points file using the attribute table manager ("manage layers" tab)
or by running v.db.connect.

For nodes created using the nodes operation (method 2 above), it is possible to create an attribute table
for the new nodes in layer 2 using the attribute table manager and connect it to layer 2 ("manage layers"
tab) or to create a table with v.db.addtable, connect it to layer 2 with v.db.connect, and update the new
table with cat values with v.to.db.

Once a vector network has been created, it can be analyzed in a number of powerful ways using the suite
of v.net.* modules. The shortest route between two nodes, following arcs, can be computed (v.net.path),
as can the shortest route that will pass through a set of nodes and return to the starting node
(v.net.salesman). Least cost routes through the network can be calculated on the basis of distance only
or on the basis of distance weighted by an attribute associated with each arc (for example, travel speed
along a network segment). A network can be divided into concentric zones of equal travel cost around one
or more nodes (v.net.iso) or subdivided so that each node is surrounded by a zone in which all arcs can
be reached with the same travel costs as all arcs surrounding each other node (v.net.alloc). In addition
to the modules listed above, the GRASS vector networking suite includes numerous other modules for
analysis of network costs and connectivity. These include: v.net.allpairs, v.net.bridge,
v.net.centrality, v.net.components, v.net.distance, v.net.flow, v.net.spanningtree, v.net.steiner,
v.net.timetable, and v.net.visibility.

NOTES
For a vector map prepared for network analysis in GRASS, nodes are represented by the grass-internal
geometry type node and arcs by the geometry type line. If vector editing is required to modify the
graph, wxGUI vector digitizer or v.edit can be used. See also the Linear Referencing System available in
GRASS GIS.

EXAMPLES
The examples are North Carolina dataset based.

Create nodes globally for all line ends and intersections:
v.net input=streets_wake output=streets_node operation=nodes
Merge in nodes from a separate map within given threshold:
v.net input=streets_wake points=firestations out=streets_net \
operation=connect thresh=500
For generating network for given vector point map is required input file in format:
[category of edge] [category of start node] [category of end node]

v.net points=geodetic_swwake_pts output=geodetic_swwake_pts_net \
operation=arcs file=- << EOF
> 1 28000 28005
> 2 27945 27958
> 3 27886 27897
> EOF

AUTHORS

       Radim Blazek, ITC-irst, Trento, Italy
       Martin  Landa,  FBK-irst  (formerly ITC-irst), Trento, Italy and CTU in Prague, Czech Republic (operation
       'connect' and 'arcs')
       Markus Metz: important fixes and improvements

       Last changed: $Date: 2013-05-23 13:01:55 -0700 (Thu, 23 May 2013) $

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       © 2003-2013 GRASS Development Team

GRASS 6.4.3                                                                                        v.net(1grass)

NAME

KEYWORDS

SYNOPSIS

DESCRIPTION

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