pgr_drivingDistance¶
Name¶
pgr_drivingDistance  Returns the driving distance from a start node.
Note
Requires to build pgRouting with support for Driving Distance.
Synopsis¶
This function computes a Dijkstra shortest path solution them extracts the cost to get to each node in the network from the starting node. Using these nodes and costs it is possible to compute constant drive time polygons. Returns a set of pgr_costResult (seq, id1, id2, cost) rows, that make up a list of accessible points.
pgr_costResult[] pgr_drivingDistance(text sql, integer source, double precision distance,
boolean directed, boolean has_rcost);
Description¶
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 id of the start point 

distance:  float8 value in edge cost units (not in projection units  they might be different). 

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 (this is probably not a useful item) 
cost:  cost to get to this node ID 
Warning
You must reconnect to the database after CREATE EXTENSION pgrouting. Otherwise the function will return Error computing path: std::bad_alloc.
History
 Renamed in version 2.0.0
Examples¶
 Without reverse_cost
SELECT seq, id1 AS node, cost
FROM pgr_drivingDistance(
'SELECT id, source, target, cost FROM edge_table',
7, 1.5, false, false
);
seq  node  cost
++
0  2  1
1  6  1
2  7  0
3  8  1
4  10  1
(5 rows)
 With reverse_cost
SELECT seq, id1 AS node, cost
FROM pgr_drivingDistance(
'SELECT id, source, target, cost, reverse_cost FROM edge_table',
7, 1.5, true, true
);
seq  node  cost
++
0  2  1
1  6  1
2  7  0
3  8  1
4  10  1
(5 rows)
The queries use the Sample Data network.
See Also¶
 pgr_alphaShape  Alpha shape computation
 pgr_pointsAsPolygon  Polygon around set of points