[talk-au] Roundabouts and routing

[morb.gis at beagle.com.au]

"The first exit (west on Ginninderra Drive) isn't being counted as an exit
because that exit point is also my entry point."

Well, I would rather represent geometrical reality than play tricks for routers.

Take a comparative example:

http://www.nearmap.com/?ll=-28.0917,153.3945&z=19&t=k
http://www.openstreetmap.org/?lat=-28.0917&lon=153.3945&zoom=18&layers=B000FTT

You can see that to get from S to W, W to N and N to E it's a graceful sweep
left, more or less tangential to the roundabout.  Whereas from W to S, there's
the left bend into the roundabout, a bit of right bend in the roundabout,
before turning left again out of the roundabout.

In the first case I have edited the entry, exit and roundabout as meeting at
exactly one node.  IMHO this represents reality and if the router can't handle
it then the router should be upgraded to suit (or its OSM-to-router-format
script suitably upgraded).

We shouldn't be "mapping for the router" to the extent it disagrees with
reality, should we?

Brendan

Quoting Ben Kelley <ben.kelley at gmail.com>:

> Heh. My sister-in-law lives near here. The directions on my eTrext Legend
> did confuse me a little at that intersection. I assumed the intersection
> hadn't been drawn quite right, but I never got around to going back and
> fixing it.
>
>  - Ben.
>
> 2009/12/17 John Henderson <snowgum at gmx.com>
>
> > Here's an example:
> >
> > http://www.osm.org/?lat=-35.205609&lon=149.027603&zoom=18
> >
> > Heading north along Florey Drive, my route takes me right (towards the
> > east) on Ginninderra Drive via the roundabout.  I should be taking the
> > third exit, but the GPS with an OSM map says to take the second exit.
> >
> > And this is because of the way the roundabout has been drawn.  The first
> > exit (west on Ginninderra Drive) isn't being counted as an exit because
> > that exit point is also my entry point.  In other words, it shows that
> > one need not actually enter the roundabout to take that first turn.
> >
> > I believe that this roundabout does not accurately represent the reality
> > of the situation.
> >
> >
>