[OSM-talk] Roundabouts and routing

[Jonathan Waller]

With regards to solution 1) I have never noticed a sliproad onto a 
roundabout tagged as junction=roundabout (UK East Midlands).  Where is 
this common practice?  If this is not too widely used then it might be 
worth retagging, but I don't know how easy it would be to automatically 
detect these.

Jonathan


On 08/09/2011 19:48, Thomas Davie wrote:
> Hi,
>
> Today I experimented with using OSM maps on my Garmin sat-nav.  The 
> one thing that I noticed was that roundabouts do not work well. The 
> problem seems to be the slip roads entering the roundabout.  The 
> sat-nav recognises them as a roundabout in themself, and because of 
> that gives some fairly poor directions, for example:
>
> • Drive 10 miles then enter roundabout.
> (Drive 10 miles)
> • Enter roundabout.
> (Enter the slip road to the roundabout)
> • Enter roundabout and take the third exit.
>
> As you can see, because of the slip road's existence the GPS does not 
> announce which exit you're expecting to take until the last minute. 
>  This means that you can't get in the right lane early enough.
>
> Proposed solutions (all of which are horrible):
> 1) Don't tag sliproads onto roundabouts as junction=roundabout, 
> instead use some other tagging scheme.  Not greatly desirable because 
> it involves a *whole* lot of retagging.
> 2) Ask garmin to fix it (doesn't sound likely).
> 3) Write some fancy heuristics in the conversion from OSM to routable 
> garmin maps that figure out when you're looking at slip roads and when 
> it's an actual roundabout (sounds unreliable).
>
> Can anyone thing of a better solution to this?
>
> Bob
>
> if (*ra4 != 0xffc78948) { return false; }
>
>
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