6. Advanced Routing Queries ¶

Routing, is not limited to pedestrians and most of the time is used for routing vehicles.

Chapter Contents

Advanced Routing Queries
- Routing for Vehicles
- Cost Manipulations
  - Exercise 10 - Vehicle routing without penalization
  - Exercise 11 - Vehicle routing with penalization

6.1. Routing for Vehicles ¶

A query for vehicle routing generally differs from routing for pedestrians:

the road segments are considered directed,
Costs can be:
- Distance
- Time
- Euros
- Pesos
- Dollars
- CO2 emittions
- Ware and tear on the vehicle, etc.
The reverse_cost attribute must be taken into account on two way streets.
- The costs should have the same units as the cost attribute
- cost and reverse_cost can be different

This is due to the fact that there are roads that are “one way”.

Depending on the geometry, the valid way:

(source, target) segment (cost >= 0 and reverse_cost < 0)
(target, source) segment (cost < 0 and reverse_cost >= 0)

So a “wrong way” is indicated with a negative value and is not inserted in the graph for processing.

For two way roads cost >= 0 and reverse_cost >= 0 and their values can be different. For example, it is faster going down hill on a sloped road. In general cost and reverse_cost do not need to be length; they can be almost anything, for example time, slope, surface, road type, etc., or they can be a combination of multiple parameters.

The following queries indicate the number of road segments, where a “one way” rule applies:

Number of (source, target) segments with cost < 0

SELECT count(*)
FROM ways
WHERE cost < 0;

 count 
-------
     0
(1 row)

Number of (target, source) segments with reverse_cost < 0

SELECT count(*)
FROM ways
WHERE reverse_cost < 0;

 count 
-------
   870
(1 row)

6.1.1. Exercise 7 - Vehicle routing - Going ¶

From the Serena hotel going to the Fish market by car.

The vehicle is going from vertex 1060 to vertex 115.
Use cost and reverse_cost columns, which are in unit degrees.

SELECT * FROM pgr_dijkstra(
    'SELECT gid AS id,
         source,
         target,
         cost_s AS cost,
         reverse_cost_s AS reverse_cost
        FROM ways',
    1060, 115,
    directed := true);

Solution to Exercise 7

6.1.2. Exercise 8 - Vehicle routing - Returning ¶

From Fish market going to the Serena hotel by car.

The vehicle is going from vertex 115 to vertex 1060.
Use cost and reverse_cost columns, which are in unit degrees.

SELECT * FROM pgr_dijkstra(
    'SELECT gid AS id,
         source,
         target,
         cost_s AS cost,
         reverse_cost_s AS reverse_cost
        FROM ways',
    115, 1060,
    directed := true);

Solution to Exercise 8

Note

On a directed graph, going and coming back routes, most of the time are different.

6.1.3. Exercise 9 - Vehicle routing when “time is money”¶

From Fish market going to the Serena hotel by taxi.

The vehicle is going from vertex 115 to vertex 1060.
The cost is $100 per hour.
Use cost_s and reverse_cost_s columns, which are in unit seconds.
The duration in hours is cost / 3600
The cost in $ is cost / 3600 * 100

SELECT * FROM pgr_dijkstra('
    SELECT gid AS id,
        source,
        target,
        cost_s / 3600 * 100 AS cost,
        reverse_cost_s / 3600 * 100 AS reverse_cost
        FROM ways',
    115, 1060);

Solution to Exercise 9

Note

Comparing with Exercise 8:

The total number of records are identical
The node sequence is identical
The edge sequence is identical
The cost and agg_cost results are directly proportional

6.2. Cost Manipulations ¶

Detail. Not all crossings are vertices in the graph

When dealing with data, being aware of what kind of data is being used, can improve results.

Vehciles can not circulate pedestrian ways,
Likewise, routing not using pedestrian ways

Will make the results closer to reality.

When converting data from OSM format using the osm2pgrouting tool, there is an additional tables: configuration

In the image above there is a detail of the tag_id of the roads.

osm way types

SELECT tag_id, tag_key, tag_value FROM configuration ORDER BY tag_id;

 tag_id |  tag_key  |     tag_value
--------+-----------+-------------------
| highway   | road
| highway   | motorway
| highway   | motorway_link
| highway   | motorway_junction
| highway   | trunk
| highway   | trunk_link
| highway   | primary
| highway   | primary_link
| highway   | secondary
| highway   | tertiary
| highway   | residential
| highway   | living_street
| highway   | service
| highway   | track
| highway   | pedestrian
| highway   | services
| highway   | bus_guideway
| highway   | path
| highway   | cycleway
| highway   | footway
| highway   | bridleway
| highway   | byway
| highway   | steps
| highway   | unclassified
| highway   | secondary_link
| highway   | tertiary_link
| cycleway  | lane
| cycleway  | track
| cycleway  | opposite_lane
| cycleway  | opposite
| tracktype | grade1
| tracktype | grade2
| tracktype | grade3
| tracktype | grade4
| tracktype | grade5
| junction  | roundabout
(36 rows)

Also on the ways table there is a column that can be used to JOIN with the configuration table.

The ways types

SELECT distinct tag_id, tag_key, tag_value
FROM ways JOIN configuration USING (tag_id)
ORDER BY tag_id;

 tag_id | tag_key  |   tag_value
--------+----------+---------------
| highway  | trunk
| highway  | trunk_link
| highway  | primary
| highway  | secondary
| highway  | tertiary
| highway  | residential
| highway  | service
| highway  | track
| highway  | path
| highway  | cycleway
| highway  | footway
| highway  | steps
| highway  | unclassified
| highway  | tertiary_link
| cycleway | opposite
(15 rows)

In this workshop, costs are going to be manipulated using the configuration table.

6.2.1. Exercise 10 - Vehicle routing without penalization ¶

From the Botanical garden to the Museum

The vehicle is going from vertex 1253 to vertex 2759.
The vehicle’s cost in this case will be in seconds.
All roads have a penalty of 1
Costs are to be multiplied by penalty
Costs wont change (times 1 leaves the value unchanged).
The configuration table is linked with the ways table by the tag_id field using a JOIN.

ALTER TABLE configuration ADD COLUMN penalty FLOAT;
-- No penalty
UPDATE configuration SET penalty=1;


SELECT * FROM pgr_dijkstra('
    SELECT gid AS id,
        source,
        target,
        cost_s * penalty AS cost,
        reverse_cost_s * penalty AS reverse_cost
    FROM ways JOIN configuration
    USING (tag_id)',
    1253, 2759);

Solution to Exercise 10

6.2.2. Exercise 11 - Vehicle routing with penalization ¶

Change the cost values for the configuration table, in such a way, that the * pedestrian roads are not used * Using residential roads its not encouraged. * Using “faster” roads is highly encouraged. * The penalty values can be changed UPDATE queries.

Note

This values are an exageration

-- Not including pedestrian ways
UPDATE configuration SET penalty=-1.0 WHERE tag_value IN ('steps','footway');
-- Penalizing with 5 times the costs
UPDATE configuration SET penalty=5 WHERE tag_value IN ('residential');
-- Encuraging the use of "fast" roads
UPDATE configuration SET penalty=0.5 WHERE tag_value IN ('tertiary');
UPDATE configuration SET penalty=0.3 WHERE tag_value
IN ('primary','primary_link',
    'trunk','trunk_link',
    'motorway','motorway_junction','motorway_link',
    'secondary');

From the Botanical garden to the Museum with penalization.

The vehicle is going from vertex 1253 to vertex 2759.
Use cost_s and reverse_cost_s columns, which are in unit seconds.
Costs are to be multiplied by penalty
The configuration table is linked with the ways table by the tag_id field using a JOIN.

SELECT * FROM pgr_dijkstra('
    SELECT gid AS id,
        source,
        target,
        cost_s * penalty AS cost,
        reverse_cost_s * penalty AS reverse_cost
    FROM ways JOIN configuration
    USING (tag_id)',
    1253, 2759);

Solution to Exercise 11

Note

Comparing with Exercise 9:

The total number of records changed.
The node sequence changed.
The edge sequence changed.
The route is avoiding the residential roads that have tag_id = 110