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NAME   -  Computes  shortest  distance via the network between the given sets of
       Finds the shortest paths  from  a  feature  'to'  to  every  feature  'from'  and  various
       information about this realtion are uploaded to the attribute table.


       vector, network, shortest path

SYNOPSIS help   [-g]  input=name  output=name   [from_layer=integer]    [from_cats=range]
       [from_where=sql_query]     [to_layer=integer]     [to_cats=range]     [to_where=sql_query]
       [to_type=string[,string,...]]  afcolumn=name  [abcolumn=name]   [--overwrite]  [--verbose]

           Use geodesic calculation for longitude-latitude locations

           Allow output files to overwrite existing files

           Verbose module output

           Quiet module output

           Name of input vector map

           Name for output vector map

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

           From category values
           Example: 1,3,7-9,13

           From WHERE conditions of SQL statement without 'where' keyword
           Example: income = 10000

           Layer number
           To layer number or name
           Default: 1

           To category values
           Example: 1,3,7-9,13

           To WHERE conditions of SQL statement without 'where' keyword
           Example: income = 10000

           To feature type
           Options: point,line,boundary
           Default: point

           Arc forward/both direction(s) cost column

           Arc backward direction cost column

DESCRIPTION finds the nearest element in set to for every point in set from.


       These  two  sets are given by the respective layer, where and cats parameters. The type of
       to features is specified by to_type parameter. All from features are points.  A  table  is
       linked to output map containing various information about the relation. More specifically,
       the table has three columns: cat, tcat and dist storing category  of  each  from  feature,
       category of the nearest to feature and the distance between them respectively. Furthemore,
       output map contains the shorest path between each cat, tcat pair.  Each  path  consist  of
       several  lines.  If  a  line is on the shorest path from a point then the category of this
       point is assigned to the line. Note that every line may contain  more  than  one  category
       value  since a single line may be on the shortest path for more than one from feature. And
       so the shortest paths can be easily obtained by querying lines with corresponding category
       The costs of arcs in forward and backward direction are specified by afcolumn and abcolumn
       columns respectively. If abcolumn is not given, the same cost is used in both directions. will not work if you are trying to find  the  nearest  neighbors  within  a
       group of nodes, i.e. where to and from are the same set of nodes, as the closest node will
       be the node itself and the result will be zero-length paths.  In  order  to  find  nearest
       neighbors  within  a  group  of nodes, you can either loop through each node as to and all
       other nodes as from or create a complete distance matrix with  and  select
       the lowest non-zero distance for each node.


       Find  shortest  path  and distance from every school to the nearest hospital and show path
       from school number one. input=city output=nearest from_where="type=school" \
                      to_where="type=hospital" afcolumn=SHAPE_LEN
       d.vect nearest cats=1



       Daniel Bundala, Google Summer of Code 2009, Student
       Wolf Bergenheim, Mentor

       Last changed: $Date: 2013-05-23 13:01:55 -0700 (Thu, 23 May 2013) $

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