pgr_trsp  Turn Restriction Shortest Path (TRSP)¶
Name¶
pgr_trsp — Returns the shortest path with support for turn restrictions.
Synopsis¶
The turn restricted shorthest path (TRSP) is a shortest path algorithm that can optionally take into account complicated turn restrictions like those found in real work navigable road networks. Performamnce wise it is nearly as fast as the A* search but has many additional features like it works with edges rather than the nodes of the network. Returns a set of pgr_costResult (seq, id1, id2, cost) rows, that make up a path.
pgr_costResult[] pgr_trsp(sql text, source integer, target integer,
directed boolean, has_rcost boolean [,restrict_sql text]);
pgr_costResult[] pgr_trsp(sql text, source_edge integer, source_pos double precision,
target_edge integer, target_pos double precision, directed boolean,
has_rcost boolean [,restrict_sql text]);
Description¶
The Turn Restricted Shortest Path algorithm (TRSP) is similar to the Shooting Star algorithm in that you can specify turn restrictions.
The TRSP setup is mostly the same as Dijkstra shortest path with the addition of an optional turn restriction table. This makes adding turn restrictions to a road network much easier than trying to add them to Shooting Star where you had to ad the same edges multiple times if it was involved in a restriction.
sql:  a SQL query, which should return a set of rows with the following columns: SELECT id, source, target, cost, [,reverse_cost] FROM edge_table



source:  int4 NODE id of the start point 

target:  int4 NODE 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. 

restrict_sql:  (optional) a SQL query, which should return a set of rows with the following columns: SELECT to_cost, target_id, via_path FROM restrictions

Another variant of TRSP allows to specify EDGE id of source and target together with a fraction to interpolate the position:
source_edge:  int4 EDGE id of the start edge 

source_pos:  float8 fraction of 1 defines the position on the start edge 
target_edge:  int4 EDGE id of the end edge 
target_pos:  float8 fraction of 1 defines the position on the end edge 
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
 New in version 2.0.0
Examples¶
 Without turn restrictions
SELECT seq, id1 AS node, id2 AS edge, cost
FROM pgr_trsp(
'SELECT id, source, target, cost FROM edge_table',
7, 12, false, false
);
seq  node  edge  cost
+++
0  7  6  1
1  8  7  1
2  5  8  1
3  6  11  1
4  11  13  1
5  12  1  0
(6 rows)
 With turn restrictions
Turn restrictions require additional information, which can be stored in a separate table:
CREATE TABLE restrictions (
rid serial,
to_cost double precision,
to_edge integer,
from_edge integer,
via text
);
INSERT INTO restrictions VALUES (1,100,7,4,null);
INSERT INTO restrictions VALUES (2,4,8,3,5);
INSERT INTO restrictions VALUES (3,100,9,16,null);
Then a query with turn restrictions is created as:
SELECT seq, id1 AS node, id2 AS edge, cost
FROM pgr_trsp(
'SELECT id, source, target, cost FROM edge_table',
7, 12, false, false,
'SELECT to_cost, to_edge AS target_id,
from_edge  coalesce('',''  via, '''') AS via_path
FROM restrictions'
);
seq  node  edge  cost
+++
0  7  6  1
1  8  7  1
2  5  8  1
3  6  11  1
4  11  13  1
5  12  1  0
(6 rows)
The queries use the Sample Data network.