pgr_bdAstarCostMatrix - proposed

Name

pgr_bdAstarCostMatrix - Calculates the a cost matrix using pgr_bdAstar.

_images/boost-inside.jpeg

Boost Graph Inside

Availability: 2.5.0

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 ANY-INTEGER and ANY-NUMERICAL
    • 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

Synopsis

Using Dijkstra algorithm, calculate and return a cost matrix.

Signature Summary

pgr_bdAstarCostMatrix(edges_sql, start_vids)
pgr_bdAstarCostMatrix(edges_sql, start_vids, [, directed , heuristic, factor, epsilon])
RETURNS SET OF (start_vid, end_vid, agg_cost)
OR EMPTY SET

Signatures

Minimal Signature

pgr_bdAstarCostMatrix(edges_sql, start_vids)
RETURNS SET OF (start_vid, end_vid, agg_cost)
OR EMPTY SET
This usage calculates the cost from the each start_vid in start_vids to each start_vid in start_vids
  • on a directed graph
  • with heuristic’s value 5
  • with factor’s value 1
  • with epsilon’s value 1
Example:Cost matrix for vertices 1, 2, 3, and 4.
SELECT * FROM pgr_bdAstarCostMatrix(
    'SELECT id, source, target, cost, reverse_cost, x1, y1, x2, y2 FROM edge_table',
    (SELECT array_agg(id) FROM edge_table_vertices_pgr WHERE id < 5)
);
 start_vid | end_vid | agg_cost 
-----------+---------+----------
         1 |       2 |        1
         1 |       3 |        6
         1 |       4 |        5
         2 |       1 |        1
         2 |       3 |        5
         2 |       4 |        4
         3 |       1 |        2
         3 |       2 |        1
         3 |       4 |        3
         4 |       1 |        3
         4 |       2 |        2
         4 |       3 |        1
(12 rows)

Complete Signature

pgr_bdAstarCostMatrix(edges_sql, start_vids, [, directed , heuristic, factor, epsilon])
RETURNS SET OF (start_vid, end_vid, agg_cost)
OR EMPTY SET
This usage calculates the cost from the each start_vid in start_vids to each start_vid in start_vids allowing the user to choose
  • if the graph is directed or undirected
  • heuristic,
  • and/or factor
  • and/or epsilon.
Example:Cost matrix for an undirected graph for vertices 1, 2, 3, and 4.

This example returns a symmetric cost matrix.

SELECT * FROM pgr_bdAstarCostMatrix(
    'SELECT id, source, target, cost, reverse_cost, x1, y1, x2, y2 FROM edge_table',
    (SELECT array_agg(id) FROM edge_table_vertices_pgr WHERE id < 5),
    false
);
 start_vid | end_vid | agg_cost 
-----------+---------+----------
         1 |       2 |        1
         1 |       3 |        2
         1 |       4 |        3
         2 |       1 |        1
         2 |       3 |        1
         2 |       4 |        2
         3 |       1 |        2
         3 |       2 |        1
         3 |       4 |        1
         4 |       1 |        3
         4 |       2 |        2
         4 |       3 |        1
(12 rows)

Description of the Signatures

Description of the edges_sql query for astar like functions

edges_sql:an SQL query, which should return a set of rows with the following columns:
Column Type Default Description
id ANY-INTEGER   Identifier of the edge.
source ANY-INTEGER   Identifier of the first end point vertex of the edge.
target ANY-INTEGER   Identifier of the second end point vertex of the edge.
cost ANY-NUMERICAL  

Weight of the edge (source, target)

  • When negative: edge (source, target) does not exist, therefore it’s not part of the graph.
reverse_cost ANY-NUMERICAL -1

Weight of the edge (target, source),

  • When negative: edge (target, source) does not exist, therefore it’s not part of the graph.
x1 ANY-NUMERICAL   X coordinate of source vertex.
y1 ANY-NUMERICAL   Y coordinate of source vertex.
x2 ANY-NUMERICAL   X coordinate of target vertex.
y2 ANY-NUMERICAL   Y coordinate of target vertex.

Where:

ANY-INTEGER:SMALLINT, INTEGER, BIGINT
ANY-NUMERICAL:SMALLINT, INTEGER, BIGINT, REAL, FLOAT

Description of the parameters of the signatures

Parameter Type Description
edges_sql TEXT Edges SQL query as described above.
start_vid ANY-INTEGER Starting vertex identifier.
start_vids ARRAY[ANY-INTEGER] Starting vertices identifierers.
end_vid ANY-INTEGER Ending vertex identifier.
end_vids ARRAY[ANY-INTEGER] Ending vertices identifiers.
directed BOOLEAN
  • Optional.
    • When false the graph is considered as Undirected.
    • Default is true which considers the graph as Directed.
heuristic INTEGER

(optional). Heuristic number. Current valid values 0~5. Default 5

  • 0: h(v) = 0 (Use this value to compare with pgr_dijkstra)
  • 1: h(v) abs(max(dx, dy))
  • 2: h(v) abs(min(dx, dy))
  • 3: h(v) = dx * dx + dy * dy
  • 4: h(v) = sqrt(dx * dx + dy * dy)
  • 5: h(v) = abs(dx) + abs(dy)
factor FLOAT (optional). For units manipulation. \(factor > 0\). Default 1. see Factor
epsilon FLOAT (optional). For less restricted results. \(epsilon >= 1\). Default 1.

Description of the return values for a Cost function

Returns set of (start_vid, end_vid, agg_cost)

Column Type Description
start_vid BIGINT Identifier of the starting vertex. Used when multiple starting vetrices are in the query.
end_vid BIGINT Identifier of the ending vertex. Used when multiple ending vertices are in the query.
agg_cost FLOAT Aggregate cost from start_vid to end_vid.

Examples

Example:Use with tsp
SELECT * FROM pgr_TSP(
    $$
    SELECT * FROM pgr_bdAstarCostMatrix(
        'SELECT id, source, target, cost, reverse_cost, x1, y1, x2, y2 FROM edge_table',
        (SELECT array_agg(id) FROM edge_table_vertices_pgr WHERE id < 5),
        false
    )
    $$,
    randomize := false
);
 seq | node | cost | agg_cost 
-----+------+------+----------
   1 |    1 |    1 |        0
   2 |    2 |    1 |        1
   3 |    3 |    1 |        2
   4 |    4 |    3 |        3
   5 |    1 |    0 |        6
(5 rows)