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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 < 1000 and inhab >= 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 < 1000 and inhab >= 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) $

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