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NAME  - Performs network maintenance.


       vector, networking, maintenance

SYNOPSIS help     [-c]     input=name     [points=name]      [output=name]      [operation=string]
       [alayer=integer]     [nlayer=integer]     [thresh=float]     [--overwrite]     [--verbose]

           Assign unique categories to new points
           For operation 'nodes'

           Allow output files to overwrite existing files

           Verbose module output

           Quiet module output

           Name of input vector map

           Name of input point vector map
           Required for operation 'connect'

           Name for output vector map

           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
           nreport: print to standard output {point_category line_category[,line_category...]}

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

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

           Required for operation 'connect'. Connect points in given threshold.

DESCRIPTION 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

       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 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). 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 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

       Once a vector network has been created, it can be analyzed in a number  of  powerful  ways
       using  the suite of* modules. The shortest route between two nodes, following arcs,
       can be computed (, as can the shortest route that will pass through  a  set  of
       nodes  and  return  to  the starting node (  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 ( 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 (  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:,,,,,,,,, and

       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.

       The examples are North Carolina dataset based.

       Create nodes globally for all line ends and intersections: input=streets_wake output=streets_node operation=nodes
        Merge in nodes from a separate map within given threshold: 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] points=geodetic_swwake_pts output=geodetic_swwake_pts_net \
             operation=arcs file=- << EOF
       > 1 28000 28005
       > 2 27945 27958
       > 3 27886 27897
       > EOF


        wxGUI vector digitizer, v.edit



       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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