[OSM-talk] Roundabouts - why is a separate segment required?
davefoxfac63 at btinternet.com
Wed Feb 14 16:39:29 UTC 2018
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?,
Or even cross-roads. The router has to check to find out what road it's
crossing & find the appropriate exit, which, in the case of cross-roads,
will be on the same node.
On 14/02/2018 16:17, Maarten Deen wrote:
> On 2018-02-14 15:53, Dave F wrote:
>> Could anyone give me an explanation for this line from
>> "Each road has to be connected with the roundabout in a separate
>> node—that is, between these nodes a segment of the roundabout is
>> I see no requirement for a separate segment:
>> * When a entering road shares a node with a roundabout then the
>> router knows it's entered that roundabout by reading the tags on the
>> circular way.
>> * Whilst on that node, the router checks to see if there are any
>> suitable exits. If there are, then it leaves the roundabout.
>> * If not, it continues going around until it finds an appropriate
> I'm not sure if you read the requirement right, but this tells mappers
> not to connect the entry and exit road on the same node. If you were
> to map it that way, the router will not see that you enter a
> roundabout and need to exit at the first exit. It will just tell you
> to go right.
> It is not (what I think you think) that there needs to be a separate
> way between entrance and exit, the roundabout can be mapped as one way
> in total.
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