[Talk-transit] Proposed Feature - RFC - Public Transport

Dominik Mahrer (Teddy) teddy at teddy.ch
Thu Dec 9 05:35:47 GMT 2010


Hi Michael

> In the new proposal I am missing some details on how to build relations:
>
> 1. Should the outward and return trip be represented as two separate
> relations, as a single relation or is that up to the mapper?

Each direction should be in a separate relation. This is written in the 
proposal. Both directions/variants should be member of a master relation.

> 2. Which members should the relation contain, and in which order?

You are not the first with this question, so I added some explanations 
to the proposal:

First the stop_positions ordered (with role stop), then platforms 
ordered (with role platform) and then the ways ordered (without role).

> 3. Which data primitive should be added for stops?

Stop positions AND platform. Stop position is important for the route 
itself, the platform is important for pedestrian routing.

> 4. How are line variants mapped?

Problem 1:

A - B1/B2 - C - D - E1/E2 - F

In morning and evening hours the bus stops at B2 instead of B1.
During school holiday the bus stops at E2 instead of E1.
This gives us four possibilities really used.

When you add alt-roles to a stop you can't say when is what route used. 
So this does not work, we need really four relations.

Problem 2:

What do you want to say with role forward/backward? Forward/backward 
compared to what? To the route direction or to the tagged way direction? 
Actually both is used in the OSM database and no one knows how to 
interpret it. Role forward and backward is in my eyes a nice try to 
solve a problem. But it confused more then it solved. We should leave 
this away.

Practical:

I map the variant with the most stops (in your example twice A B1 E1 K. 
In JOSM you can easily copy a relation and change what is different. So 
to handle your 8 variants should not take 8 times mapping one variant.

I personally leave away the very special cases (ex. first course starts 
at B instead of A). This is only relevant when timetable information is 
added to.



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