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

NAME

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DESCRIPTION

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