[mkgmap-dev] [PATCH v5] - drive on left + roundabout direction checking

Tue Oct 27 23:52:56 GMT 2009

Hi Dermot,

On Tue, 27 Oct 2009 23:36:17 +0000
Dermot McNally <dermotm at gmail.com> wrote:

> I love the roundabout warnings and, with their help, I've been able to
> fix all the broken roundabouts in Ireland that they have identified.
> 
> In the process, though, I've spotted a particular kind of false
> positive that I suspect we can avoid. Consider this way:
> 
> http://www.openstreetmap.org/browse/way/43100358
> 
> Before I split this way, it went directly from the roundabout west as
> N52, connecting in the process to the terriary road to its south
> _which itself connects to the roundabout_. Neither road has flares
> mapped for it. I got the following warning:
> 
> 2009/10/27 23:20:25 WARNING (RouteNode): Incoming roundabout flare
> road (N52, http://www.openstreetmap.org/browse/way/43100358) points in
> wrong direction?
> http://www.openstreetmap.org/?lat=53.25524&lon=-7.53688&zoom=17
> 
> My interpretation is that, since these roads connect to the roundabout
> and then to each other, they must be flare ways. My suggestion is that
> there should be a certain reasonable maximum length within which flare
> ways are expected to connect together, and that otherwise, they be
> considered normal roads.

Your analysis is good. I have spotted this situation occurring
occasionally in the UK roundabouts I have been fixing (as of
this evening, I have fixed 71% of 2226 flare road errors and other
misc roundabout related breakage in the GB data). So far, my solution
in this situation is just to partition one of the "fake flares" so
that it will no longer trigger a warning.

Your suggestion to avoid the warning is probably OK - perhaps the
max distance should be scaled by the distance between the nodes on the
roundabout i.e. if the flare roads are longer than, say, 5 times the
distance between the nodes where the flares join the roundabout. That's
easy to implement and should be correct most of the time.

Have you seen any of the roundabout forks/overlaps errors?

Thanks for the feedback, I'm glad it's useful to you.

Cheers,

Mark