# pgr_bdAstar - Bi-directional A* Shortest Path¶

## Name¶

pgr_bdAstar - Returns the shortest path using Bidirectional A* algorithm.

## Synopsis¶

This is a bi-directional A* search algorithm. It searches from the source toward the distination and at the same time from the destination to the source and terminates whe these to searches meet in the middle. Returns a set of pgr_costResult (seq, id1, id2, cost) rows, that make up a path.

pgr_costResult[] pgr_bdAstar(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 int4 identifier of the source vertex int4 identifier of the target vertex float8 value, of the edge traversal cost. A negative cost will prevent the edge from being inserted in the graph. x coordinate of the start point of the edge y coordinate of the start point of the edge x coordinate of the end point of the edge y coordinate of the end point of the edge (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 node ID edge ID (-1 for the last row) cost to traverse from id1 using id2

Warning

You must reconnect to the database after CREATE EXTENSION pgrouting. Otherwise the function will return Error computing path: std::bad_alloc.

History

• New in version 2.0.0

## Examples¶

• Without reverse_cost
SELECT * FROM pgr_bdAStar(
'SELECT id::INTEGER, source::INTEGER, target::INTEGER, cost, x1, y1, x2, y2
FROM edge_table',
4, 10, false, false);
seq | id1 | id2 | cost
-----+-----+-----+------
0 |   4 |   3 |    0
1 |   3 |   5 |    1
2 |   6 |  11 |    1
3 |  11 |  12 |    0
4 |  10 |  -1 |    0
(5 rows)

• With reverse_cost
SELECT * FROM pgr_bdAStar(
'SELECT id::INTEGER, source::INTEGER, target::INTEGER, cost, x1, y1, x2, y2, reverse_cost
FROM edge_table ',
4, 10, true, true);
seq | id1 | id2 | cost
-----+-----+-----+------
0 |   4 |   3 |    1
1 |   3 |   5 |    1
2 |   6 |   8 |    1
3 |   5 |  10 |    1
4 |  10 |  -1 |    0
(5 rows)


The queries use the Sample Data network.