Ubuntu Manpage: v.net.distance - Computes shortest distance via the network between the given sets of

NAME

       v.net.distance   -  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.

KEYWORDS

       vector, network, shortest path

SYNOPSIS

       v.net.distance
       v.net.distance help
       v.net.distance   [-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]

   Flags:
       -g
           Use geodesic calculation for longitude-latitude locations

       --overwrite
           Allow output files to overwrite existing files

       --verbose
           Verbose module output

       --quiet
           Quiet module output

   Parameters:
       input=name
           Name of input vector map

       output=name
           Name for output vector map

       from_layer=integer
           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_cats=range
           From category values
           Example: 1,3,7-9,13

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

       to_layer=integer
           Layer number
           To layer number or name
           Default: 1

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

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

       to_type=string[,string,...]
           To feature type
           Options: point,line,boundary
           Default: point

       afcolumn=name
           Arc forward/both direction(s) cost column

       abcolumn=name
           Arc backward direction cost column

DESCRIPTION

       v.net.distance finds the nearest element in set to for every point in set from.

NOTES

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.

v.net.distance 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 v.net.allpairs and select
the lowest non-zero distance for each node.

EXAMPLES

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

AUTHORS

       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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       © 2003-2013 GRASS Development Team