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

[Warin]

On 12-May-17 07:45 AM, Tijmen Stam wrote:
> On 10-05-17 18:59, Bjoern Hassler wrote:
>> Hello again,
>>
>> 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?
>>
>> Thanks!
>> Bjoern
>>
>> 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?
>
> Answering your grand question:
>
> As I interpret the wiki, it is the route-relation that ties together 
> the stop_position with the platform, by including them as a pair per 
> "halt".
>
> Imagine the "renderer" is a transit simulator that simulates a journey 
> from your home to somewhere via "Green line" that stops on track 1 
> (platform A), then the route relation of the green line contains both 
> the stop_position (a node on track 1) and the platform (platform A).
> It would then plot a walking route to platform A, then transfers you 
> into the train (on track 1) and along the route.
>
> I know of people who use a stop_area-relation for each 
> stop_position/platform pair, which then could be used to tie 
> stop_position and platform together, but that is not how I interpret 
> the wiki.
> I use one stop_area for a whole station.

Here there are different length trains - they usually stop at different 
positions on the platform so the middle of the train is at the middle of 
the platform. And there are short platforms where a full length train is 
too long for the platform - so people wanting to get off must be either 
in the front carriages, the middle carriages or the rear carriages in 
order to get off. (Why the different options? So that the train 
passengers don't all congregate in one portion of the train - different 
platforms have different positions for the train stop) Of course shorter 
length trains can stop with their carriages fully engaged with the 
platform.
I take the stop position from the train divers point of view - as that 
is what would be designated to be of practical use.