pgr_dijkstraNearCost - Proposed - pgRouting Manual (3.3)
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pgr_dijkstraNearCost - Proposed
pgr_dijkstraNearCost
- Using dijkstra algorithm, finds the route that leads to
the nearest vertex.
Warning
Proposed functions for next mayor release.
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They are not officially in the current release.
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They will likely officially be part of the next mayor release:
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The functions make use of ANY-INTEGER and ANY-NUMERICAL
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Name might not change. (But still can)
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Signature might not change. (But still can)
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Functionality might not change. (But still can)
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pgTap tests have being done. But might need more.
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Documentation might need refinement.
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![images/boost-inside.jpeg](images/boost-inside.jpeg)
Availability
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Version 3.3.0
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Promoted to proposed function
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Version 3.2.0
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New experimental function
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Description
Given a graph, a starting vertex and a set of ending vertices, this function finds the shortest path from the starting vertex to the nearest ending vertex.
Characteristics
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Uses Dijkstra algorithm.
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Works for directed and undirected graphs.
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When there are more than one path to the same vertex with same cost:
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The algorithm will return just one path
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Optionally allows to find more than one path.
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When more than one path is to be returned:
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Results are sorted in increasing order of:
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aggregate cost
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Within the same value of aggregate costs:
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results are sorted by (source, target)
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Running time: Dijkstra running time: \(drt = O((E + V)logV)\)
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One to Many; \(drt\)
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Many to One: \(drt\)
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Many to Many: \(drt * Starting vids\)
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Combinations: \(drt * Starting vids\)
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Signatures
Summary
pgr_dijkstraNearCost(Edges SQL, Start vid, End vids [, directed] [, cap])
pgr_dijkstraNearCost(Edges SQL, Start vids, End vid [, directed] [, cap])
pgr_dijkstraNearCost(Edges SQL, Start vids, End vids [, directed] [, cap], [global])
pgr_dijkstraNearCost(Edges SQL, Combinations SQL [, directed] [, cap], [global])
RETURNS SET OF (start_vid, end_vid, agg_cost)
OR EMPTY SET
One to Many
pgr_dijkstraNearCost(Edges SQL, Start vid, End vids [, directed] [, cap])
RETURNS SET OF (start_vid, end_vid, agg_cost)
OR EMPTY SET
- Example :
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Departing on car from vertex \(2\) find the nearest subway station.
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Using a directed graph for car routing.
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The subway stations are on the following vertices \(\{ 3, 6, 7\}\)
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The defaults used:
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directed => true
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cap => 1
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1SELECT * FROM pgr_dijkstraNearCost(
2 'SELECT id, source, target, cost, reverse_cost FROM edge_table',
3 2, ARRAY[3, 6, 7]
4);
5 start_vid end_vid agg_cost
6-----------+---------+----------
7 2 6 2
8(1 row)
9
The result shows that station at vertex \(6\) is the nearest.
Many to One
pgr_dijkstraNearCost(Edges SQL, Start vids, End vid [, directed] [, cap])
RETURNS SET OF (start_vid, end_vid, agg_cost)
OR EMPTY SET
- Example :
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Departing on a car from a subway station find the nearest two stations to vertex \(2\)
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Using a directed graph for car routing.
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The subway stations are on the following vertices \(\{ 3, 6, 7\}\)
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On line 4 : using the positional parameter: directed set to
true
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In line 5 : using named parameter cap => 2
1SELECT * FROM pgr_dijkstraNearCost(
2 'SELECT id, source, target, cost, reverse_cost FROM edge_table',
3 ARRAY[3, 6, 7], 2,
4 true,
5 cap => 2
6);
7 start_vid end_vid agg_cost
8-----------+---------+----------
9 3 2 1
10 6 2 2
11(2 rows)
12
The result shows that station at vertex \(3\) is the nearest and the next best is \(6\) .
Many to Many
pgr_dijkstraNearCost(Edges SQL, Start vids, End vids [, directed] [, cap], [global])
RETURNS SET OF (start_vid, end_vid, agg_cost)
OR EMPTY SET
- Example :
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Find the best pedestrian connection between two lines of buses
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Unsing an undirected graph for pedestrian routing
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The first subway line stations stops are at \(\{3, 6, 7\}\)
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The second subway line stations are at \(\{4, 9\}\)
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On line 4 : using the named parameter: directed => false
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The defaults used:
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cap => 1
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global => true
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1SELECT * FROM pgr_dijkstraNearCost(
2 'SELECT id, source, target, cost, reverse_cost FROM edge_table',
3 ARRAY[4, 9], ARRAY[3, 6, 7],
4 directed => false
5);
6 start_vid end_vid agg_cost
7-----------+---------+----------
8 4 3 1
9(1 row)
10
For a pedestrian the best connection is to get on/off is at vertex \(3\) of the first subway line and at vertex \(4\) of the second subway line.
Only
one
route is returned because
global
is
true
and
cap
is
1
Combinations
pgr_dijkstraNearCost(Edges SQL, Combinations SQL [, directed] [, cap], [global])
RETURNS SET OF (start_vid, end_vid, agg_cost)
OR EMPTY SET
- Example :
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Find the best car connection between all the stations of two subway lines
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Using a directed graph for car routing.
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The first subway line stations stops are at \(\{3, 6, 7\}\)
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The second subway line stations are at \(\{4, 9\}\)
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line 3 sets the start vertices to be from the fisrt subway line and the ending vertices to be from the second subway line
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line 5 sets the start vertices to be from the first subway line and the ending vertices to be from the first subway line
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On line 6 : using the named parameter is global => false
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The defaults used:
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directed => true
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cap => 1
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1SELECT * FROM pgr_dijkstraNearCost(
2 'SELECT id, source, target, cost, reverse_cost FROM edge_table',
3 'SELECT unnest(ARRAY[3, 6, 7]) as source, target FROM (SELECT unnest(ARRAY[4, 9]) AS target) a
4 UNION
5 SELECT unnest(ARRAY[4, 9]), target FROM (SELECT unnest(ARRAY[3, 6, 7]) AS target) b',
6 global => false
7);
8 start_vid end_vid agg_cost
9-----------+---------+----------
10 4 3 1
11 6 9 1
12 9 6 1
13 3 9 2
14 7 9 4
15(5 rows)
16
From the results:
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making a connection from the first subway line to the second:
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\({(3 -> 9) (6 -> 9) (7 -> 9)}\) and the best one is \((6 -> 9)\) with a cost of \(1\) (line: 11 )
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making a connection from the second subway line to the first:
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\({(4 -> 3) (9 -> 6)}\) and both are equaly good as they have the same cost. (lines: 10 and 12 )
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Parameters
Parameter |
Type |
Default |
Description |
---|---|---|---|
Edges SQL |
|
Edges query as described below |
|
Combinations SQL |
|
Combinations query as described below |
|
Start vid |
|
Identifier of the starting vertex of the path. |
|
Start vids |
|
Array of identifiers of starting vertices. |
|
End vid |
|
Identifier of the ending vertex of the path. |
|
End vids |
|
Array of identifiers of ending vertices. |
|
directed |
|
|
|
cap |
|
1 |
Find at most
|
global |
|
|
|
Inner query
Edges query
Column |
Type |
Default |
Description |
---|---|---|---|
id |
|
Identifier of the edge. |
|
source |
|
Identifier of the first end point vertex of the edge. |
|
target |
|
Identifier of the second end point vertex of the edge. |
|
cost |
|
Weight of the edge (source, target)
|
|
reverse_cost |
|
-1 |
Weight of the edge (target, source) ,
|
Where:
- ANY-INTEGER :
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SMALLINT, INTEGER, BIGINT
- ANY-NUMERICAL :
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SMALLINT, INTEGER, BIGINT, REAL, FLOAT
Combinations query
Column |
Type |
Default |
Description |
---|---|---|---|
source |
|
Identifier of the first end point vertex of the edge. |
|
target |
|
Identifier of the second end point vertex of the edge. |
Where:
- ANY-INTEGER :
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SMALLINT, INTEGER, BIGINT
Return Columns
Returns SET OF
(start_vid,
end_vid,
agg_cost)
Column |
Type |
Description |
---|---|---|
start_vid |
|
Identifier of the starting vertex. |
end_vid |
|
Identifier of the ending vertex. |
agg_cost |
|
Aggregate cost from
|
See Also
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Sample Data network.
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boost: https://www.boost.org/libs/graph/doc/table_of_contents.html
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Wikipedia: https://en.wikipedia.org/wiki/Dijkstra%27s_algorithm
Indices and tables