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v.net(1grass) Grass User's Manual v.net(1grass)

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. It permits to insert missing nodes or arcs and to connect unconnected nodes to the network within a given distance threshold. It can also report the current network graph status.
In terms of network analysis, a network consists of nodes connected by arcs. In a vector map prepared for network analysis, nodes are represented by the grass-internal geometry type node and arcs by the geometry type line. If a line consists of several vertices and segments (the typical case), only its starting and ending vertex are regarded as network nodes. Further more, explicit starting and ending nodes for e.g. least cost path search or subnetwork allocation are represented by the geometry type point which must be identical with the start or end vertex (network node) of a line.
In general, network analysis will find the least costly (shortest or fastest) path from point A to point B by follwing the existing lines. This implies that the points A, B must lie at the start or end point of a line with is part of the network. If no line is starting or ending at a given point, this point is not part of the network, i.e. the point is unconnected and unreachable.

NOTES

If vector editing is required to modify the graph, v.digit or v.edit can be used. Separately, Linear Referencing System is available in GRASS.

EXAMPLES

Spearfish based examples:
Create nodes globally for all line ends and intersections:
 
 
v.net input=roads output=roads_node operation=nodes
 
Merge in nodes from a separate map within given threshold:
 
 
echo "1|601955.1|4916944.9|start
 
2|594385.6|4921565.2|end" | v.in.ascii in=- cat=1 x=2 y=3 out=startend col="cat integer, \
 

east double precision, north double precision, label varchar(6)"
 
 
#create lines map connecting points to network (on layer 2)
 
v.net myroads points=startend out=myroads_net op=connect thresh=200
 

SEE ALSO

v.digit, v.edit, v.net.iso, v.net.path, v.net.steiner, v.net.salesman

AUTHORS

Radim Blazek, ITC-Irst, Trento, Italy
 
Martin Landa, FBK-Irst, Trento, Italy
Last changed: $Date: 2011-11-14 09:27:31 +0100 (Mon, 14 Nov 2011) $
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GRASS 6.4.2