pgr_astar - Shortest Path A*

Name

pgr_astar — Returns the shortest path using A* algorithm.

Synopsis

The A* (pronounced “A Star”) algorithm is based on Dijkstra’s algorithm with a heuristic that allow it to solve most shortest path problems by evaluation only a sub-set of the overall graph. Returns a set of pgr_costResult (seq, id1, id2, cost) rows, that make up a path.

pgr_costResult[] pgr_astar(sql text, source integer, target integer,
                       directed boolean, has_rcost boolean);

Description

sql:

a SQL query, which should return a set of rows with the following columns:

SELECT id, source, target, cost, x1, y1, x2, y2 [,reverse_cost] FROM edge_table
id:int4 identifier of the edge
source:int4 identifier of the source vertex
target:int4 identifier of the target vertex
cost:float8 value, of the edge traversal cost. A negative cost will prevent the edge from being inserted in the graph.
x1:x coordinate of the start point of the edge
y1:y coordinate of the start point of the edge
x2:x coordinate of the end point of the edge
y2:y coordinate of the end point of the edge
reverse_cost:(optional) the cost for the reverse traversal of the edge. This is only used when the directed and has_rcost parameters are true (see the above remark about negative costs).
source:

int4 id of the start point
target:

int4 id of the end point
directed:

true if the graph is directed
has_rcost:

if true, the reverse_cost column of the SQL generated set of rows will be used for the cost of the traversal of the edge in the opposite direction.

Returns set of pgr_costResult[]:

seq:row sequence
id1:node ID
id2:edge ID (-1 for the last row)
cost:cost to traverse from id1 using id2

History

  • Renamed in version 2.0.0

Examples

  • Without reverse_cost
      SELECT seq, id1 AS node, id2 AS edge, cost
              FROM pgr_astar(
                      'SELECT id, source, target, cost, x1, y1, x2, y2 FROM edge_table',
                      4, 1, false, false
              );

 seq | node | edge | cost
-----+------+------+------
   0 |    4 |   16 |    1
   1 |    9 |    9 |    1
   2 |    6 |    8 |    1
   3 |    5 |    4 |    1
   4 |    2 |    1 |    1
   5 |    1 |   -1 |    0

(6 rows)
  • With reverse_cost
SELECT seq, id1 AS node, id2 AS edge, cost
        FROM pgr_astar(
                'SELECT id, source, target, cost, x1, y1, x2, y2, reverse_cost FROM edge_table',
                4, 1, true, true
        );

 seq | node | edge | cost
-----+------+------+------
   0 |    4 |    3 |    1
   1 |    3 |    2 |    1
   2 |    2 |    1 |    1
   3 |    1 |   -1 |    0
(4 rows)

The queries use the Sample Data network.