[OSM-talk] Roundabouts - why is a separate segment required?
davefoxfac63 at btinternet.com
Wed Feb 14 17:50:37 UTC 2018
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.
> The same at this roundabout, going from Wapping Road to Commercial
> Road it will tell you to "turn left into Commercial Road" and not to
> "enter the roundabout and exit at the first exit into Commercial Road".
Noting my comment above, if a router doesn't tell you the latter, then
it's a poor program. Commercial Rd is the first exit
> 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. If
it can do it at intersections it can do it on roundabouts.
Roundabouts are just another type of intersection.
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