.TH v.net 1grass "" "GRASS 6.4.4" "Grass User's Manual"
.SH NAME
\fI\fBv.net\fR\fR  - Performs network maintenance.
.SH KEYWORDS
vector, networking, maintenance
.SH SYNOPSIS
\fBv.net\fR
.br
\fBv.net help\fR
.br
\fBv.net\fR [\-\fBc\fR] \fBinput\fR=\fIname\fR  [\fBpoints\fR=\fIname\fR]   [\fBoutput\fR=\fIname\fR]   [\fBoperation\fR=\fIstring\fR]   [\fBalayer\fR=\fIinteger\fR]   [\fBnlayer\fR=\fIinteger\fR]   [\fBthresh\fR=\fIfloat\fR]   [\-\-\fBoverwrite\fR]  [\-\-\fBverbose\fR]  [\-\-\fBquiet\fR] 
.SS Flags:
.IP "\fB\-c\fR" 4m
.br
Assign unique categories to new points
.br
For operation 'nodes'
.IP "\fB\-\-overwrite\fR" 4m
.br
Allow output files to overwrite existing files
.IP "\fB\-\-verbose\fR" 4m
.br
Verbose module output
.IP "\fB\-\-quiet\fR" 4m
.br
Quiet module output
.PP
.SS Parameters:
.IP "\fBinput\fR=\fIname\fR" 4m
.br
Name of input vector map
.IP "\fBpoints\fR=\fIname\fR" 4m
.br
Name of input point vector map
.br
Required for operation 'connect'
.IP "\fBoutput\fR=\fIname\fR" 4m
.br
Name for output vector map
.IP "\fBoperation\fR=\fIstring\fR" 4m
.br
Operation to be performed
.br
Options: \fInodes,connect,report,nreport\fR
.br
Default: \fInodes\fR
.br
\fBnodes\fR: new point is placed on each node (line end) if doesn't exist
.br
\fBconnect\fR: connect still unconnected points to vector network by inserting new line(s)
.br
\fBreport\fR: print to standard output {line_category start_point_category end_point_category}
.br
\fBnreport\fR: print to standard output {point_category line_category[,line_category...]}
.IP "\fBalayer\fR=\fIinteger\fR" 4m
.br
Arc layer
.br
A single vector map can be connected to multiple database tables. This number determines which table to use.
.br
Default: \fI1\fR
.IP "\fBnlayer\fR=\fIinteger\fR" 4m
.br
Node layer
.br
A single vector map can be connected to multiple database tables. This number determines which table to use.
.br
Default: \fI2\fR
.IP "\fBthresh\fR=\fIfloat\fR" 4m
.br
Threshold
.br
Required for operation 'connect'. Connect points in given threshold.
.PP
.SH DESCRIPTION
\fIv.net\fR is used for network preparation and maintenance. Its 
main use is to create a vector network from vector lines (\fIarcs
\fR) and points (\fInodes\fR) by creating nodes from 
intersections in a map of vector lines (\fInode\fR operator), by 
connecting a vector lines map with a points map (\fIconnect\fR 
operator), and by creating new lines between pairs of vector points
(\fIarcs\fR operator).
.PP
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 \fIv.net.path\fR 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). 
.PP
\fIv.net\fR offers two ways to add nodes to a network of arcs:
..IP
.IP \fB1\fR
Use the \fIconnect\fR 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 \fIthresh\fR (threshold) distance to a line/boundary
will be connected as network nodes.
.IP \fB2\fR
Create nodes and arcs from a vector line/boundary file using the \fInode\fR
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 \fIarc\fR that consists of several segments connected by 
vertices (the typical case), only the starting and ending vertices are 
treated as network nodes.
.PP
    
.PP
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. 
.PP
For nodes created using the \fIconnect\fR 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 \fIv.db.connect\fR.
.PP
For nodes created using the \fInodes\fR 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
\fIv.db.addtable\fR, 
connect it to layer 2 with \fIv.db.connect\fR,
and update the new table with cat values with \fIv.to.db\fR. 
.PP
Once a vector network has been created, it can be analyzed in a number
of powerful ways using the suite of \fIv.net\fR.* modules. The shortest route 
between two nodes, following arcs, can be computed
(\fIv.net.path\fR), as can the 
shortest route that will pass through a set of nodes and return to the 
starting node (\fIv.net.salesman\fR).
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 (\fIv.net.iso\fR) 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 (\fIv.net.alloc\fR).
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: 
\fIv.net.allpairs\fR, 
\fIv.net.bridge\fR, 
\fIv.net.centrality\fR, 
\fIv.net.components\fR, 
\fIv.net.distance\fR, 
\fIv.net.flow\fR, 
\fIv.net.spanningtree\fR, 
\fIv.net.steiner\fR, 
\fIv.net.timetable\fR, and 
\fIv.net.visibility\fR.
.SS NOTES
For a vector map prepared for network analysis in GRASS, nodes are 
represented by the grass-internal geometry type \fInode\fR and arcs 
by the geometry type \fIline\fR. 
If vector editing is required to modify the
graph, \fIwxGUI vector
digitizer\fR or \fIv.edit\fR can be
used. 
See also the Linear Referencing System available in
GRASS GIS.
.SS EXAMPLES
The examples are North Carolina dataset based.
.PP
Create nodes globally for all line ends and intersections:
\fC
.DS
.br
v.net input=streets_wake output=streets_node operation=nodes
.br
.DE
\fR
Merge in nodes from a separate map within given threshold:
\fC
.DS
.br
v.net input=streets_wake points=firestations out=streets_net \(rs
.br
      operation=connect thresh=500
.br
.DE
\fR
For generating network for given vector point map is required input 
file in format:
\fC
.DS
.br
[category of edge] [category of start node] [category of end node]
.br
.DE
\fR
\fC
.DS
.br
v.net points=geodetic_swwake_pts output=geodetic_swwake_pts_net \(rs
.br
      operation=arcs file=- << EOF
.br
> 1 28000 28005
.br
> 2 27945 27958
.br
> 3 27886 27897
.br
> EOF
.br
.DE
\fR
.SH SEE ALSO
\fI
wxGUI vector digitizer,
v.edit
\fR
.PP
\fI
v.net.alloc,
v.net.allpairs,
v.net.bridge,
v.net.centrality,
v.net.components,
v.net.connectivity,
v.net.distance,
v.net.flow,
v.net.iso,
v.net.path,
v.net.salesman
v.net.spanningtree,
v.net.steiner,
v.net.timetable,
v.net.visibility
\fR
.SH AUTHORS
Radim Blazek, ITC-irst, Trento, Italy
.br
Martin Landa, FBK-irst (formerly ITC-irst), Trento, Italy and CTU in
Prague, Czech Republic (operation 'connect' and 'arcs')
.br
Markus Metz: important fixes and improvements
.PP
\fILast changed: $Date: 2013-05-23 22:01:55 +0200 (Thu, 23 May 2013) $\fR
.PP
Full index
.PP
© 2003-2014 GRASS Development Team