[Routing] Roundabouts - why is a separate segment required?

[Dave F]

On 14/02/2018 16:46, Marcus Wolschon wrote:
>
> A nice example of 2 shared nodes making up 1 exit.

Err. it's clearly one node, with one entrance, one exit, & one continue.

>
>
>
> Irrelevant to your point but not to mine.

Err.. but it was my point being discussed. I started the thread!

> Or do you proclaim that e.g. accurate graphical rendering of a map is 
> not important for anyone?

Are you serious? The reason I mapped it as such was to make it accurate. 
Adding a separate section would make it *inaccurate*

> That pedestian crossings on the legs of a roundabout are not important 
> for anyone?
> That the roundabout-segment a postbox is at is not important for anyone?
>
> Also for vehicle routing, calculating the metrics as preicsely as 
> possible is a major
> quality factor in good routing. So if using a roundabout is much 
> slower itself and
> slows you down in front of (decellerating) and behind the roundabout 
> (accelerating)
> compared to a simple right-turn, then this is an imporant thing to 
> model correctly.
>
> If a construction site or traffic jam blocks one exit, your model 
> would block the entire roundabout
> instead of just that exist. Causing the driver to be routed way around 
> that intersection while for
> his/her particular route it poses not much of an issue.

Again, I think you've gone way off piste.

DaveF