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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

SEE ALSO

        wxGUI vector digitizer, v.edit

          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

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) $

       Full index

       © 2003-2013 GRASS Development Team



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