[talk-au] Roundabouts and routing

[John Henderson]

To me it seems an important aspect of OSM that its routable maps work 
well.  I had been using my Garmin 76CSx with OSM maps to check this 
functionality.

Because the screen is too small for thorough hands-free checking, I've 
just bought a Garmin Nuvi 1350.  I'm finding that using this to direct 
me to locations I already know the way to is a very effective way to 
"ground truth" the OSM map I load onto it.

One very common issue I'm encountering is the exit count on roundabouts. 
  I usually get correct counts with the supplied Garmin/Sensis maps, and 
often get wrong counts with OSM.

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.

I don't use Navit, and wonder if Navit users are seeing the same issue.

I have been editing and fixing cases like this as I come across them. 
But I'd like to get the opinions of others, and even suggest a mention 
in the "Australian Tagging Guidelines" if there's agreement.

John