PostGIS Cookbook - Second Edition

osm2pgrouting is a powerful tool that handles a lot of the translation of OSM data into a format that can be used in pgRouting. In this case, it creates eight tables from our input file. Of those eight, we'll address the two primary tables: the ways table and the nodes table.

Our ways table is a table of the lines that represent all our streets, roads, and trails that are in OSM. The nodes table contains all the intersections. This helps us identify the beginning and end points for routing.

Let's apply an A* ("A star") routing approach to this problem.

A* is an extension of Dijkstra's algorithm which uses a heuristic to speed up the search for the shortest path, at the cost of occasionally not finding the optimum route. See http://en.wikipedia.org/wiki/A* and http://en.wikipedia.org/wiki/File:Astar_progress_animation.gif for more information.

You will recognize the following syntax from Dijkstra:

WITH astar AS (
  SELECT * FROM pgr_astar(
    'SELECT gid AS id, source, target,
     length AS cost, x1, y1, x2, y2 
     FROM chp06.cleveland_ways', 89475, 14584, false
  )

)

SELECT gid, the_geom
FROM chp06.cleveland_ways w, astar a
WHERE w.gid = a.edge;

The following screenshot shows the results displayed on a map (map tiles by Stamen Design, under CC BY 3.0; data by OpenStreetMap, under CC BY SA):

Sample calculated route with pgRouting visualized in QGIS

Table of Contents for
PostGIS Cookbook - Second Edition

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Table of Contents for PostGIS Cookbook - Second Edition

Table of Contents for
PostGIS Cookbook - Second Edition