7. Writing a SQL Stored Procedures ¶

pgRouting functions provide low level interface. When developing for a higher level application, the requirements need to be represented in the SQL queries. As these SQL queries get more complex, it is desirable to store them in postgreSQL stored procedures. Stored procedures are an effective way to wrap application logic, in this case, related to routing logic.

Chapter Contents

Writing a SQL Stored Procedures

7.1. The application requirements ¶

The stored procedure that is going to be developed has the following requirements:

Vehicles are routed.
- Do not use pedestrian roads.
- Once the VIEW is created, it is going to be used on the other requirements.
- Exercise 10 - Vehicle routing with access restrictions solves using a CASE statement.
- Costs are to be in minutes.
  - Exercise 4 - Many Pedestrians going to different destinations. solves a pedestrian routing in minutes.
Starting and ending vertices are by selection using osm_id.
- In past chapters was done using the id of the vertices.
Name of the road on the path.
The geometry segments along the route path with the corrent orientation.
- Geometry is to be returned.
- Azimuth in degrees of the geometry is to be returned
- Geometry handling to get the correct orientation.

7.1.1. Exercise 1 - Segments for Vehicle Routing ¶

The vehicle can not circulate on non pedestrian roads

Create a view of the allowed road network for circulation.
Routing costs will be based on minutes.
Verify the reduced number of road segments

-- DROP VIEW vehicle_net CASCADE;

CREATE VIEW vehicle_net AS
    SELECT gid,
        source,
        target,
        -- converting to minutes
        cost_s / 60 AS cost,
        reverse_cost_s / 60 AS reverse_cost,
        the_geom
    FROM ways JOIN osm_way_classes AS c
    USING (class_id)
    WHERE  c.name NOT IN ('pedestrian','steps','footway','path');

-- Verification
SELECT count(*) FROM ways;
SELECT count(*) FROM vehicle_net;

Solution to Chapter 7 Exercise 1

7.1.2. Exercise 2 - Limiting the Road Network within an Area ¶

View of smaller set of roads for vehicles

The vehicle can only circulate inside this Boundig Box: (-71.05 42.34, -71.03 42.35)

The vehicle can only circulate inside the bounding box: (-71.05 42.34, -71.03 42.35)
Create a view of the allowed road network for circulation.
Use the vehicle_net VIEW.
Verify the reduced number of road segments

-- DROP VIEW little_net;

CREATE VIEW little_net AS
    SELECT *
    FROM vehicle_net
    WHERE vehicle_net.the_geom && ST_MakeEnvelope(-71.05, 42.34,-71.03, 42.36);

-- Verification
SELECT count(*) FROM little_net;

Solution to Chapter 7 Exercise 2

7.1.3. Exercise 3 - Route using “osm_id”¶

From the Venue to the Brewry using the osm_id.

The vehicle is going from vertex 61350413 to vertex 61479912.
Start and end vertex are given with their osm_id.
The result should contain:
- seq for ordering and unique row identifier
- the name of the road segments

SELECT *
FROM pgr_dijkstra(
    'SELECT gid AS id, * FROM vehicle_net',
    -- source
    (SELECT id FROM ways_vertices_pgr WHERE osm_id = 61350413),
    -- target
    (SELECT id FROM ways_vertices_pgr WHERE osm_id = 61479912));

Solution to Chapter 7 Exercise 3

7.1.4. Exercise 4 - Get additional information ¶

From the Venue to the Brewry, additionally get the name of the roads.

The vehicle is going from vertex 61350413 to vertex 61479912.
The result should also contain:
- the name of the road segments

SELECT dijkstra.*, ways.name
FROM pgr_dijkstra(
    'SELECT gid AS id, * FROM vehicle_net',
    (SELECT id FROM ways_vertices_pgr WHERE osm_id = 61350413),
    (SELECT id FROM ways_vertices_pgr WHERE osm_id = 61479912)
    ) AS dijkstra
LEFT JOIN ways
ON (edge = gid) ORDER BY seq;

Solution to Chapter 7 Exercise 4

7.2. Geometry handling ¶

7.2.1. Exercise 5 - Route geometry (human readable)¶

From the Venue to the Brewry, additionally get the geometry in human readable form.

The vehicle is going from vertex 61350413 to vertex 61479912.
Include the geometry of the path in human readable form.

SELECT dijkstra.*, ways.name, ST_AsText(ways.the_geom)
FROM pgr_dijkstra(
    'SELECT gid AS id, * FROM vehicle_net',
    (SELECT id FROM ways_vertices_pgr WHERE osm_id = 61350413),
    (SELECT id FROM ways_vertices_pgr WHERE osm_id = 61479912)
    ) AS dijkstra
LEFT JOIN ways
ON (edge = gid) ORDER BY seq;

Solution to Chapter 7 Exercise 5

Note

The last record of the result, does not contain a geometry value since the shortest path function returns -1 for the last record to indicate the end of the route.

7.2.2. Exercise 6 - Route geometry (binary format)¶

From the Venue, going to the Brewry by car, also get the binary format geometry that can be used by a front end app.

Note

Not using ST_AsText gives the binary format.

Tip

WITH provides a way to write auxiliary statements in larger queries. It can be thought of as defining temporary tables that exist just for one query.

The vehicle is going from vertex 61350413 to vertex 61479912.
Include the geometry of the path in default binary format.

WITH
dijkstra AS (
    SELECT * FROM pgr_dijkstra(
        'SELECT gid AS id, * FROM vehicle_net',
        (SELECT id FROM ways_vertices_pgr WHERE osm_id = 61350413),
        (SELECT id FROM ways_vertices_pgr WHERE osm_id = 61479912))
)
SELECT dijkstra.*, ways.name, ways.the_geom AS route_geom 
FROM dijkstra LEFT JOIN ways ON (edge = gid)
ORDER BY seq;

Solution to Chapter 7 Exercise 6

7.2.3. Exercise 7 - Using the geometry ¶

From the Venue to the Brewry, calculate the azimuth in degrees.

The vehicle is going from vertex 61350413 to vertex 61479912.
Get the seq, name, cost, azimuth in degrees and the geomtery
The geometry of the route path in human readable form & binary form

WITH
dijkstra AS (
    SELECT * FROM pgr_dijkstra(
        'SELECT gid AS id, * FROM vehicle_net',
        (SELECT id FROM ways_vertices_pgr WHERE osm_id = 61350413),
        (SELECT id FROM ways_vertices_pgr WHERE osm_id = 61479912))
),
get_geom AS (
    SELECT dijkstra.*, ways.name, ways.the_geom AS route_geom 
    FROM dijkstra JOIN ways ON (edge = gid)
    ORDER BY seq)
SELECT seq, name, cost,
    -- calculating the azimuth
    degrees(ST_azimuth(ST_StartPoint(route_geom), ST_EndPoint(route_geom))) AS azimuth,
    ST_AsText(route_geom),
    route_geom
FROM get_geom
ORDER BY seq;

Solution to Chapter 7 Exercise 7

7.2.4. Exercise 8 - Geometry directionality ¶

From the Venue, going to the Brewry by car, get the geometry with correct arrow directionality.

When we generate a route the segements are returned as the geometry in the database. that means the segments can be reverserd relative to the direction of the route path. Goal is to have all segments oriented correctly along the route path.

The vehicle is going from vertex 61350413 to vertex 61479912.
The first point of the segment must “match” with the last point of the previous segment.
Get the seq, name, cost, azimuth and the geomtery
The geometry of the route path in human readable form & binary form

WITH
dijkstra AS (
    SELECT * FROM pgr_dijkstra(
        'SELECT gid AS id, * FROM vehicle_net',
        (SELECT id FROM ways_vertices_pgr WHERE osm_id = 61350413),
        (SELECT id FROM ways_vertices_pgr WHERE osm_id = 61479912))
),
get_geom AS (
    SELECT dijkstra.*, ways.name,
        -- adjusting directionality
        CASE
            WHEN dijkstra.node = ways.source THEN the_geom
            ELSE ST_Reverse(the_geom)
        END AS route_geom
    FROM dijkstra JOIN ways ON (edge = gid)
    ORDER BY seq)
SELECT seq, name, cost,
    degrees(ST_azimuth(ST_StartPoint(route_geom), ST_EndPoint(route_geom))) AS azimuth,
    ST_AsText(route_geom),
    route_geom
FROM get_geom
ORDER BY seq;

Solution to Chapter 7 Exercise 8

Note

Comparing row 1 & 2 from Solution to Chapter 7 Exercise 5

-- from Exercise 5
LINESTRING(-71.0414012 42.3502602,-71.040802 42.351054)
LINESTRING(-71.0415194 42.3501037,-71.0414012 42.3502602)

-- from Excercise 7
LINESTRING(-71.040802 42.351054,-71.0414012 42.3502602)
LINESTRING(-71.0414012 42.3502602,-71.0415194 42.3501037)

In Exercise 5 the first point of the second segment does not match the last point of the first segment
In Exercise 7 the first point of the second segment matches the last point of the first segment

7.3. Creating a Function ¶

The following function simplifies (and sets default values) when it calls the shortest path Dijkstra function.

Tip

pgRouting uses heavely function overloading:

Avoid the name of a function installed with pgRouting
Avoid the name of a function starting with pgr_ & ST_

7.3.1. Exercise 9 - Function for an application ¶

Putting all together in a SQL function

Basically the
Should work for any given area.
Data tables:
- the edges are found in ways
- the vertices are found in ways_vertices_pgr
Allow a view as a parameter
- A table can be used if the columns have the correct names
Start and end vertex are given with their osm_id.
The result should contain:
- seq, name, cost, azimuth and the geomtery
- The geometry of the route path in human readable form & binary form

--DROP FUNCTION wrk_dijkstra(regclass, bigint, bigint);

CREATE OR REPLACE FUNCTION wrk_dijkstra(
        IN edges_subset regclass,
        IN source BIGINT,
        IN target BIGINT,
        OUT seq INTEGER,
        OUT gid BIGINT,
        OUT name TEXT,
        OUT cost FLOAT,
        OUT azimuth FLOAT,
        OUT route_readable TEXT,
        OUT route_geom geometry
    )
    RETURNS SETOF record AS
$BODY$
    WITH
    dijkstra AS (
        SELECT * FROM pgr_dijkstra(
            -- using parameters instead of specific values
            'SELECT gid AS id, * FROM ' || $1,
            (SELECT id FROM ways_vertices_pgr WHERE osm_id = $2),
            (SELECT id FROM ways_vertices_pgr WHERE osm_id = $3))
    ),
    get_geom AS (
        SELECT dijkstra.*, ways.name,
            CASE
                WHEN dijkstra.node = ways.source THEN the_geom
                ELSE ST_Reverse(the_geom)
            END AS route_geom
        FROM dijkstra JOIN ways ON (edge = gid)
        ORDER BY seq)
    SELECT
        seq,
        edge,  -- will get the name "gid"
        name,
        cost,
        degrees(ST_azimuth(ST_StartPoint(route_geom), ST_EndPoint(route_geom))) AS azimuth,
        ST_AsText(route_geom),
        route_geom
    FROM get_geom
    ORDER BY seq;
$BODY$
LANGUAGE 'sql';

Solution to Chapter 7 Exercise 9

7.3.2. Exercise 10 - Using the function ¶

The osm_id must exist on the ways_vertices_pgr table.
If an osm_id falls outside the view, No path will be returned.

SELECT *
FROM wrk_dijkstra('vehicle_net',  61350413, 61479912);

Solution to Chapter 7 Exercise 10

Note

Try the function with little_net and a combination of the interesting places:

61350413 is the Seaport Hotel & World Trade Center.
61441749 is the Central Parking at the Airport.
61479912 is the Harpoon Brewery.
61493634 is the Market Place.
1718017636 is the Westin Boston Waterfront.
2481136250 is the New England Aquarium

7.3.3. Exercise 11 - Saving the function ¶

Save the function code above into a file ~/Desktop/workshop/dijkstraHeading.sql.

Saving functions in a file can be used to install the functionin another database. Install the function into the database with:

psql -U user -d city_routing -f ~/Desktop/workshop/wrk_dijkstra.sql