On 2018-02-14 18:50, Dave F wrote:
On 14/02/2018 17:13, Maarten Deen wrote:
On 2018-02-14 17:39, Dave F wrote:
I think I have read it correctly.


It is easy to determine this shared node is part of the roundabout as
well as the entrance from Wapping & can exit along Commercial, or if
required, continue around the roundabout:
How is this different from, say, two side roads joining a main road at
the same node?,

Because a machine can not determine if you are actually entering the roundabout or not.

Yes it can. It has the junction=roundabout tag on the way.

Technically speaking you are not because you are just touching one node of the roundabout.

Yes you are. You may not be on there very long, but you approach the
roundabout, pass the signs saying it's a roundabout, give way to those
already on it, you enter it & then indicate that you're leaving it.

Not from a data standpoint.

Just connecting to a road on a node does not mean you enter that road. The same at intersections, if you cross a road (connected by a node) you do not enter that road so you do not need instructions for it.

A router has to be aware of it & know what it's attributes are, to
decide if it needs to go along it. It does this from a *single* node.

It doesn't work like that anywhere in OSM. I can cross a road that I'm not allowed to drive on. The router does not need to know anything about the road that I'm crossing and I can always cross a road that I'm not allowed to enter.
It would make mapping extremely awkward if that were not so.


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