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NAME   -  Computes  shortest distance via the network between
       the given sets of features.
       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]  [--quiet]

           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 number.
       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) $

       Full index

       © 2003-2013 GRASS Development Team

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