Guida rapida pgRouting¶

pgRouting è un’estensione che aggiunge funzionalità di routing e altre analisi di rete ai database PostGIS/PostgreSQL.

Contenuti

Abilita pgRouting in un database
Caricamento dei dati OSM con osm2pgrouting
Controlla i dati importati
Inner Query
pgr_Dijkstra
E ora?

Abilita pgRouting in un database ¶

In questo esempio creererai un database chiamato city_routing e abiliterai pgRouting nel database.

Apri una finestra System Tools ‣ QTerminal ed eseguire lo strumento a riga di comando confezionato con PostgreSQL psql.

psql

Al prompt di psql, digita:

CREATE DATABASE city_routing;
\connect city_routing;
CREATE EXTENSION pgrouting CASCADE;

Puoi verificare la tua installazione eseguendo questo:

SELECT * FROM pgr_version();

pgr_version
-------------
 3.1.0
(1 row)

La tua versione dovrebbe essere 3.1.0 o superiore

Esci dal database

\q

Caricamento dei dati OSM con osm2pgrouting ¶

osm2pgrouting è uno strumento a riga di comando per caricare file .osm nel database con un formato compatibile con pgRouting.

Controlla la versione installata

osm2pgrouting --version

La risposta mostra

This is osm2pgrouting Version 2.3.6

Carica i dati dal file osm:

bzcat data/osm/feature_city.osm.bz2 > /tmp/feature_city.osm
osm2pgrouting \
  -f /tmp/feature_city.osm \
  -h localhost \
  -U user \
  -d city_routing \
  -p 5432 \
  -W user \
  --conf=/usr/share/osm2pgrouting/mapconfig_for_cars.xml
rm /tmp/feature_city.osm

L’output dovrebbe essere qualcosa come:

Execution starts at: Thu Jan 21 16:25:38 2021

***************************************************
           COMMAND LINE CONFIGURATION             *
***************************************************
Filename = /tmp/feature_city.osm
Configuration file = /usr/share/osm2pgrouting/mapconfig_for_cars.xml
host = localhost
port = 5432
dbname = city_routing
username = user
schema=
prefix =
suffix =
Don't drop tables
Don't create indexes
Don't add OSM nodes
***************************************************
Testing database connection: city_routing
database connection successful: city_routing
Connecting to the database
connection success

Creating tables...
TABLE: ways_vertices_pgr created ... OK.
TABLE: ways created ... OK.
TABLE: pointsofinterest created ... OK.
TABLE: configuration created ... OK.
Opening configuration file: /usr/share/osm2pgrouting/mapconfig_for_cars.xml
    Parsing configuration

Exporting configuration ...
  - Done
Counting lines ...
  - Done
Opening data file: /tmp/feature_city.osm        total lines: 844044
    Parsing data


End Of file


    Finish Parsing data

Adding auxiliary tables to database...

Export Ways ...
    Processing 37373 ways:
[**************************|                        ] (53%) Total processed: 20000       Vertices inserted: 8126        Split ways inserted 10253
[**************************************************|] (100%) Total processed: 37373      Vertices inserted: 1423        Split ways inserted 3385

Creating indexes ...

Processing Points of Interest ...
#########################
size of streets: 37373
Execution started at: Thu Jan 21 16:25:38 2021
Execution ended at:   Thu Jan 21 16:25:42 2021
Elapsed time: 4.645 Seconds.
User CPU time: -> 2.36362 seconds
#########################

Controlla i dati importati ¶

Connetti al database city_routing

psql city_routing

Il comando \d elencherà tutte le tabelle e le sequenze disponibili

                  List of relations
 Schema |           Name           |   Type   | Owner
--------+--------------------------+----------+-------
 public | configuration            | table    | user
 public | configuration_id_seq     | sequence | user
 public | geography_columns        | view     | user
 public | geometry_columns         | view     | user
 public | pointsofinterest         | table    | user
 public | pointsofinterest_pid_seq | sequence | user
 public | spatial_ref_sys          | table    | user
 public | ways                     | table    | user
 public | ways_gid_seq             | sequence | user
 public | ways_vertices_pgr        | table    | user
 public | ways_vertices_pgr_id_seq | sequence | user
(11 rows)

osm2pgrouting carica gli identificatori OSM osm_id e genera anche un identificatore univoco per tutti i dati: id sui vertici, gid sui bordi.

SELECT id, osm_id
FROM ways_vertices_pgr
WHERE id IN(100,600);

I risultati sono:

 id  |  osm_id
-----+----------
 100 | 81622364
 600 | 82708785
(2 rows)

Inner Query ¶

La maggior parte delle funzioni pgRouting hanno un parametro che è un’istruzione SQL, si chiama inner query

Lo statement SQL interno deve sempre avere i nomi dei campi id, source, target, e cost con reverse_cost come opzionale.

Query interna che usa gid come identificatore dei segmenti

SELECT gid as id,
       source, target,
       cost, reverse_cost
FROM ways

Query interna che usa gid come identificatore dei segmenti e la lunghezza come costo senza l’opzionale reverse_cost.

SELECT gid as id,
       source, target,
       length AS cost
FROM ways

pgr_Dijkstra ¶

Esegui la funzione di percorso più breve di Dijkstra basata sul tempo in secondi per attraversare un segmento su un grafo indiretto, usando id come identificatore di un vertice

SELECT *
FROM pgr_dijkstra(
  'SELECT gid as id,
          source, target,
          cost_s AS cost, reverse_cost_s AS reverse_cost
  FROM ways',
  100, 600,
  directed => false
);

I risultati sono:

 seq | path_seq | node | edge  |      cost          |       agg_cost
-----+----------+------+-------+--------------------+--------------------
|        1 |  100 |  6199 |  8.994104012024671 |                  0
|        2 | 4360 |   152 | 2.8524015038110697 |  8.994104012024671
|        3 |  101 |   511 | 2.4123361340227754 |  11.84650551583574
|        4 |  322 |   707 |   3.63955931676029 | 14.258841649858514
|        5 |  448 |   705 | 2.9567136964053367 | 17.898400966618805
|        6 |  445 |   662 |  4.185190538775397 | 20.855114663024143
|        7 |  415 |   663 | 1.2667248968947813 |  25.04030520179954
|        8 |  442 |   699 |  6.371427985640729 |  26.30703009869432
|        9 |  593 |   913 | 2.5897354220718807 |  32.67845808433505
|       10 |  438 |   693 | 5.5261229396496585 |  35.26819350640693
|       11 | 1573 |  2421 |  7.003475952839719 |  40.79431644605659
|       12 |  619 | 10389 | 3.8659203494409344 |  47.79779239889631
|       13 |  600 |    -1 |                  0 |  51.66371274833725
(13 rows)

Una query che usa l’identificatore OSM diventa:

SELECT *
FROM pgr_dijkstra(
  'SELECT gid as id,
          source_osm AS source, target_osm AS target,
          cost_s AS cost, reverse_cost_s AS reverse_cost
  FROM ways',
  81622364, 82708785,
  directed => false
);

Poiché la query usa i campi source_osm e target_osm, la query li aliasfica per avere i nomi richiesti source e target.

Il risultato è:

 seq | path_seq |    node    | edge  |        cost        |      agg_cost
-----+----------+------------+-------+--------------------+--------------------
|        1 |   81622364 |  6199 |  8.994104012024671 |                  0
|        2 | 1177972556 |   152 | 2.8524015038110697 |  8.994104012024671
|        3 |   81622365 |   511 | 2.4123361340227754 |  11.84650551583574
|        4 |   81917858 |   707 |   3.63955931676029 | 14.258841649858514
|        5 |   82582021 |   705 | 2.9567136964053367 | 17.898400966618805
|        6 |   82581909 |   662 |  4.185190538775397 | 20.855114663024143
|        7 |   82571671 |   663 | 1.2667248968947813 |  25.04030520179954
|        8 |   82581612 |   699 |  6.371427985640729 |  26.30703009869432
|        9 |   82708510 |   913 | 2.5897354220718807 |  32.67845808433505
|       10 |   82580320 |   693 | 5.5261229396496585 |  35.26819350640693
|       11 |   97825917 |  2421 |  7.003475952839719 |  40.79431644605659
|       12 |   82714784 | 10389 | 3.8659203494409344 |  47.79779239889631
|       13 |   82708785 |    -1 |                  0 |  51.66371274833725
(13 rows)

I costi sono gli stessi della prima query

Una query per ottenere la geometria del percorso

I risultati di pgr_dijkstra devono essere uniti alla tabella ways.

SELECT seq, edge, rpad(b.the_geom::text,60,' ') AS "the_geom (truncated)"
FROM pgr_dijkstra(
  'SELECT gid as id,
          source, target,
          cost_s AS cost, reverse_cost_s AS reverse_cost
  FROM ways',
  100, 600,
  directed => false
) AS a
JOIN ways AS b ON (a.edge = b.gid) ORDER BY seq;

I risultati, per scopi visivi sono troncati qui, le geometrie sono molto più lunghe di quanto mostrato

 seq | edge  |                     the_geom (truncated)
-----+-------+--------------------------------------------------------------
|  6199 | 0102000020E6100000050000009F3825C56C3C4DC0D8367B56884A41C011
|   152 | 0102000020E610000003000000B586F7C19E3C4DC016A0127C784A41C034
|   511 | 0102000020E610000002000000EFF7D566AD3C4DC09C267D6B714A41C04A
|   707 | 0102000020E6100000060000004A247612B63C4DC0FA1F05F4674A41C052
|   705 | 0102000020E610000003000000964E35C4C23C4DC0D81E076F594A41C095
|   662 | 0102000020E610000002000000504FC4C7CC3C4DC00858AB764D4A41C01F
|   663 | 0102000020E610000002000000408C6BD7DF3C4DC013ACBBC3374A41C01F
|   699 | 0102000020E61000000300000082FD7C00F73C4DC0E44FAFEF1E4A41C017
|   913 | 0102000020E610000002000000650D28E5FF3C4DC03D02C985144A41C082
|   693 | 0102000020E610000002000000C761D5C5123D4DC060E05E3EFE4941C065
|  2421 | 0102000020E610000003000000675F1ED72B3D4DC0A45F11B2E24941C05F
| 10389 | 0102000020E6100000020000006CA9CD49393D4DC08E548440D34941C067
(12 rows)

Con il comando \q chiudi la shell di PostgreSQL.

E ora?¶

sito web di pgRouting - Visita il sito web del progetto https://pgrouting.org per saperne di più su pgRouting.
pgRouting Documentazione - Trova la documentazione più recente in https://docs.pgrouting.org.
pgRouting Workshop - Il workshop «FOSS4G routing with pgRouting tools and OpenStreetMap road data» è disponibile in: https://workshop.pgrouting.org.
osm2pgRouting loading data - https://github.com/pgRouting/osm2pgrouting/wiki/Documentation-for-osm2pgrouting-v2.3

Guida rapida pgRouting¶

Abilita pgRouting in un database¶

Caricamento dei dati OSM con osm2pgrouting¶

Controlla i dati importati¶

Inner Query¶

pgr_Dijkstra¶