Openstreetmaps - continuous road?

Question

I imported the OSM data for Switzerland in Postgres and I am interested in getting the road data of a continuous part of a highway (I know the name),that is, the part that connects two specific cities. The highway is quite big (A1) and connects a lot of cities together.

I am not sure how the sequence of road segments is stored in postgres (ie, how one knows that one road segment is directly after the other). How should I query Postgres to get a linestring with the route from on city to another? I can visualize the data of the whole highway (which spans multiple cities) in QuantumGis by doing the query:

select osm_id,way from planet_osm_roads where highway='motorway' and ref='A1';

but I don't know how to only get the osm_ids that I am interested in, in the order they appear in the route. I do not want to do a bounding box constraint in the where clauses because I am looking for a general solution and also, I am still not sure how the order of the sequence of road segments is saved.

Answer 1

The way I did that was to use pgrouting, namely, their pgr_dijkstra algorithm. I loaded the OSM data into a format fit for use by pgrouting using the osm2pgrouting tool.