# pgRouting Manual (2.1.0)

## pgr_drivingDistance (V2.0)

## Name

`pgr_drivingDistance` - Returns the driving distance from a start node.

## 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);

Warning

This signature is being deprecated on version 2.1, Please use it without the `has_rcost` flag instead:

`pgr_drivingDistance(sql, start_v, distance, directed)`

See pgr_drivingDistance

## 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

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.
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
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 |    7 |    0
       1 |    8 |    1
    (2 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 |    7 |    0
       1 |    8 |    1
    (5 rows)

The queries use the Sample Data network.

## See Also

- pgr_alphaShape - Alpha shape computation
- pgr_pointsAsPolygon - Polygon around set of points