[OSM-dev] osm2pgsql patch for nested relations

[Michael Heißmeier]

Hi,

the current scheme for mapping public transportation 
(http://wiki.openstreetmap.org/wiki/Proposed_features/Public_Transport) uses 
nested relations. The primary information about a line (reference, operator 
etc.) is stored in a master relation which contains relations for the different 
directions or variants.

When osm2pgsql imports such relations it converts them into lines with all the 
tags attached. But in this case the information from the master relation is not 
forwarded. Several osm-based maps showing public transportation thus do no 
longer show the line number along the route displayed (cf. the recent discussion 
in German on 
http://wiki.openstreetmap.org/wiki/Talk:%C3%96pnvkarte#Relations_aus_Routen) as 
soon as people enter them according to the new scheme.

I dug into the sources and found a solution which is attached as a patch. As I 
am certainly no expert in osm2pgsql's database handling I am open for any 
comments. If a solution along these lines could be integrated (maybe guarded by 
an option) this would restore the functionality of the maps mentioned without 
inspiring people to attach all tags at all relations just to get rendering working.


--
Michael

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