[OSM-talk] Roundabouts - why is a separate segment required?

Maarten Deen mdeen at xs4all.nl
Wed Feb 14 16:17:14 UTC 2018


On 2018-02-14 15:53, Dave F wrote:
> Hi
> Could anyone give me an explanation for this line from
> https://wiki.openstreetmap.org/wiki/Tag:junction=roundabout
> 
> "Each road has to be connected with the roundabout in a separate
> node—that is, between these nodes a segment of the roundabout is
> required."
> 
> 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
> exit.

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.

Maarten



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