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NAME  - Computes the shortest path between all pairs of nodes in the network.


       vector, network, shortest path

SYNOPSIS help    [-ga]    input=name    output=name     [layer=integer]      [cats=range]
       [where=sql_query]     [afcolumn=name]     [abcolumn=name]     [--overwrite]    [--verbose]

           Use geodesic calculation for longitude-latitude locations

           Add points on nodes without points

           Allow output files to overwrite existing files

           Verbose module output

           Quiet module output

           Name of input vector map

           Name for output vector map

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

           Category values
           Example: 1,3,7-9,13

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

           Name of arc forward/both direction(s) cost column

           Name of arc backward direction cost column

DESCRIPTION computes the shortest  path  between  each  selected  node  and  all  other
       selected nodes. An attribute table is created and linked to layer 1 of the output map. The
       table contains three columns: cat, to_cat, cost.  Each  entry  denotes  the  cost  of  the
       shortest  path  from cat to to_cat. If the cost is negative then no path exists. If points
       are specified by cats, layer or where parameters then the table is  filled  only  for  the
       selected points.

       If abcolumn is not given then then the same costs are used for forward and backward arcs.

       Contrary  to  other*  modules, does not allow to use arcs and nodes
       from separate layers.  This means that you have to put both types  of  features  into  the
       same  layer, but with distinct category numbers in order to allow accessing specific nodes
       only. See the example below.


       If the -a flag is set then new points are added on nodes without nodes. These points  have
       the  largest  category. Precisely, the category value of each new point is larger than any
       of the old categories. Note that these new points are not included in the output table.


       Find shortest path along roads between schools (North Carolina sample dataset):
       #check cat values in arcs layer (streets_wake here):
       v.category streets_wake op=report
       #take the existing cat values of the points in schools_wake and add
       50000 (because the cat values in streets_wake go up to just under 50000)
       v.category schools_wake out=schools op=sum cat=50000
       #now link the nodes with their new categories to the arcs, with node  category  values  in
       layer 1 streets_wake points=schools op=connect thresh=200 out=network
       #then launch your analysis indicating the cat values of the points which you want to use network cats=50000-50167 out=allpairs
       #get distance matrix allpairs



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

       Last changed: $Date: 2012-10-24 01:13:53 -0700 (Wed, 24 Oct 2012) $

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