pgr_dijkstraNearCost  Experimental¶
pgr_dijkstraNearCost
— Using dijkstra algorithm, finds the route that leads to
the nearest vertex.
Warning
Possible server crash
These functions might create a server crash
Warning
Experimental functions
They are not officially of the current release.
They likely will not be officially be part of the next release:
The functions might not make use of ANYINTEGER and ANYNUMERICAL
Name might change.
Signature might change.
Functionality might change.
pgTap tests might be missing.
Might need c/c++ coding.
May lack documentation.
Documentation if any might need to be rewritten.
Documentation examples might need to be automatically generated.
Might need a lot of feedback from the comunity.
Might depend on a proposed function of pgRouting
Might depend on a deprecated function of pgRouting
Availability
Version 3.2.0
New experimental function
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¶
Uses Dijkstra algorithm.
Works for directed and undirected graphs.
When there are more than one path to the same vertex with same cost:
The algorithm will return just one path
Optionally allows to find more than one path.
When more than one path is to be returned:
Results are sorted in increasing order of:
aggregate cost
Within the same value of aggregate costs:
results are sorted by (source, target)
Running time: Dijkstra running time: \(drt = O((E + V)logV)\)
One to Many; \(drt\)
Many to One: \(drt\)
Many to Many: \(drt * Starting vids\)
Combinations: \(drt * Starting vids\)
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
Departing on car from vertex \(2\) find the nearest subway station.
Using a directed graph for car routing.
The subway stations are on the following vertices \(\{ 3, 6, 7\}\)
The defaults used:
directed => true
cap => 1
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
Departing on a car from a subway station find the nearest two stations to vertex \(2\)
Using a directed graph for car routing.
The subway stations are on the following vertices \(\{ 3, 6, 7\}\)
On line 4: using the positional parameter: directed set to
true
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
Find the best pedestrian connection between two lines of buses
Unsing an undirected graph for pedestrian routing
The first subway line stations stops are at \(\{3, 6, 7\}\)
The second subway line stations are at \(\{4, 9\}\)
On line 4: using the named parameter: directed => false
The defaults used:
cap => 1
global => true
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
Find the best car connection between all the stations of two subway lines
Using a directed graph for car routing.
The first subway line stations stops are at \(\{3, 6, 7\}\)
The second subway line stations are at \(\{4, 9\}\)
line 3 sets the start vertices to be from the fisrt subway line and the ending vertices to be from the second subway line
line 5 sets the start vertices to be from the first subway line and the ending vertices to be from the first subway line
On line 6: using the named parameter is global => false
The defaults used:
directed => true
cap => 1
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:
making a connection from the first subway line to the second:
\({(3 > 9) (6 > 9) (7 > 9)}\) and the best one is \((6 > 9)\) with a cost of \(1\) (line: 11)
making a connection from the second subway line to the first:
\({(4 > 3) (9 > 6)}\) and both are equaly good as they have the same cost. (lines: 10 and 12)
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:
 ANYINTEGER
SMALLINT, INTEGER, BIGINT
 ANYNUMERICAL
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:
 ANYINTEGER
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¶
Sample Data network.
boost: https://www.boost.org/libs/graph/doc/table_of_contents.html
Wikipedia: https://en.wikipedia.org/wiki/Dijkstra%27s_algorithm
Indices and tables