On 15/02/2018 10:05, Maarten Deen wrote:
On 2018-02-14 19:39, Dave F wrote:
On 14/02/2018 18:23, Johan C wrote:
No, they are not. Roundabouts are special types of intersections.
Which is another type of intersection.
They have a way on which you can drive round. And round. And round.
And they have other ways leading to and from this round way.
Whenever you enter the roundabout you drive on this round way, even
if it's just for a metre. And then you exit this round way on to a
different way.
The present tagging (used since 2005 or so, and all around the
globe) is fine.
To repeat myself. You can determine if you need to "drive on this
round way" from a single node. No need for a section between entrance
You can not determine that from a single node. You need to load the
whole way that connects to that node
But that what happens in all roundabout situations. You enter at a node
& read the tags of the way which contains that node. Having an exit way
attached to that node doesn't prevent this.
https://www.openstreetmap.org/node/5408566797
and than make a judgement call which roads connected to that node you
will traverse (which you don't know, because from a topology
standpoint you are not traversing that way).
In my example you can see you're on a roundabout & there's an exit. You
can load both ways & calculate the correct direction to take, similar to
a crossroads at a single node.
It is like Matej's example.
Suppose it is mapped with the entry and exit road connected to one
node. Yes, you can see if there also connects a roundabout to that
node and you can make the determination that in that case you need to
traverse the roundabout in the correct direction.
But suppose there is not a roundabout connected but a (circular) way
with a oneway direction. Then you also need to make the decision that
you have to traverse that way.
But suppose the way is not circular (making you cross or touch a
oneway street), than you can not do that.
When is a road circular? Most roads are circular from a topology
standpoint, as in: you can reach a node on that way going in either
direction. So you can not determine from a topology standpoint if a
road is a circular road or a roundabout.
If what you say were to be true you would have problems navigating all
types of junctions. Every junction is entered at a *node* all connected
way's information is loaded by processing that node.
DaveF
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