[Tagging] Feature Proposal - TMC - New tagging scheme for TMC

[Eckhart Wörner]

Hi,

Am Mittwoch, 11. April 2012, 15:42:29 schrieb fly:
> I still do not get one major point which was totally left out on the first
> scheme. What actually belongs to a "point" and how are they tagged. 
Especially
> on big crossings and roundabouts I always was confused (e.g. it might be
> possible that a part of this point is blocked but how do I know which one 
and
> you might be able to use  the first/last exit/entrance of a junction but not 
the
> rest. )

Indeed, this is what I was worried about as well.
Here's a proposed (partial) fix, which starts from the original proposal.

Let's assume that 123, 456 and 789 are connected LCD which describe a road. 
Further assume that at 456 there's a big intersection.
Then:
- All ways between 123 and 456 are marked tmc=DE:123+456, and all ways between 
456 and 789 are marked tmc=DE:456+789.
- All ways on the intersection 456 leading from 123 to 789 are then marked 
tmc=DE:456+.

This has several advantages:
- A traffic jam between 123 and 456 will not block the intersection 456 anymore.
- Exits are defined as follows:  an exit at 456 in positive direction starts at 
a way that is tagged either tmc=DE:456+ or tmc=DE:123+456 ("from"), uses a 
node that is part of a way tagged either tmc=DE:456+ or tmc=DE:456+789 ("via") 
and ends at a way that is tagged neither tmc=DE:456+ nor tmc=DE:456+789, nor 
tmc=DE:123+456 ("to"). An exit is therefore a maneuver. This may sound a bit 
technical at first, but none of this is exposed to the tagging, and the idea of 
an exit is probably quite intuitive.
- Likewise, entries are defined.
- Automatic consistency checking is still possible, as there are no holes.

There is at least one issue that still has to be addressed: this tagging does 
not imply an ordering of the exits / entries; it is not clear what the first, 
second… exit would be.

Eckhart Wörner