[Tagging] rail routes: how are platforms and stops associated (rail question 2)

[Michael Reichert]

Hi Bjoern,

Am 2017-05-10 um 18:59 schrieb Bjoern Hassler:
> In an  osm:relation:route
> <https://wiki.openstreetmap.org/wiki/relation:route> (type=route,
> route=train/...), you have both platforms and stop positions. How is a
> particular platform associated with a stop that serves it?
> 
> E.g. for public transport routing, you'd walk (highway=footway) to a
> platform (public_transport=platform), at which point you'd change to a
> train stopping at a stop (public_transport=stop_position). How would the
> routing algorithm know that the platform is associated with the stop?
> 
> Is there an existing mechanism or convention, e.g. a tag on the platform
> that indicates the stop, or both tagged with the same name or similar?

Stop positions can have a tag ref=* or local_ref=* giving the track
number which is signed on the platform. The platform has ref=*, too. The
ref tag of the platform often contains multiple numbers because many
platforms have to edges, i.e. ref=2;3 or even worse: ref=2a;2b;2;3a;3b;3
(if the track can be occupied by two trains behind each other at the
same time – very common at busy stations).

If you don't want to parse ref=*/local_ref=* and route relations are
properly mapped, you can check which route relations reference a
platform. If a route relation contains both platforms and stop
positions, the next member of a relation after a stop position node is
should be the platform.

I think that both variants provide better results than simple snapping
on the next edge in your pedestrian routing graph (if platforms are in
your routing graph). There are cases in reality where a railway track
has platforms on both sides but you can or must leave the train only to
one direction.

> PS I've noticed that sometimes the stop position is at the far end of a
> platform (i.e. the two stop positions are at opposite ends of the station).
> Maybe that's so that an association can be made?

From my point of view this is wrong mapping. (In Germany mainly done by
user rayquaza) To give a correct answer, you should give some examples
(node IDs).

Best regards

Michael

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