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

From Mark Burton markb at ordern.com on Sun Oct 4 19:49:48 BST 2009

Hi Charlie,

> I must be doing something wrong.  I've just run this on the UK using 
> --drive-on-left and --check-roundabouts and it seems to be flagging 
> roundabouts that are correct (i.e. clock-wise).
> Here's some examples:
> 2009/10/04 19:16:31 WARNING (StyledConverter): Roundabout 4831867 
> direction is wrong - reversing it (see 
> http://www.openstreetmap.org/?lat=58.98532&lon=-2.95700&zoom=17)
> 2009/10/04 19:16:31 WARNING (StyledConverter): Roundabout 27448831 
> direction is wrong - reversing it (see 
> http://www.openstreetmap.org/?lat=56.49183&lon=-2.99837&zoom=17)
> 2009/10/04 19:16:31 WARNING (StyledConverter): Roundabout 27449021 
> direction is wrong - reversing it (see 
> http://www.openstreetmap.org/?lat=56.48717&lon=-3.00616&zoom=17)

They have all been fixed by me a few days ago - perhaps your data is
> There are also slightly different roundabout-related messages, e.g.
> 2009/10/04 19:16:30 WARNING (StyledConverter): Roundabout segment 
> 7730805 direction looks wrong (see 
> http://www.openstreetmap.org/?lat=57.15204&lon=-2.29254&zoom=17)
> I can't see what these warnings refer to.

Roundabout segments are ways that have been tagged as a roundabout but
don't actually make a loop themselves. Hopefully, a number of segments
make up a complete roundabout. This would be the case if, say, some
portion of the roundabout was in a relation and the rest was not. Also,
if the roundabout involves bridges it won't all be in one piece.

Whereas detecting the direction of a roundabout is easy and, if the
direction is not what is expected, the roundabout can be reversed
without fear of screwing up. The same cannot be said for segments of a
roundabout. i.e. their direction is not always obvious. In my trawl
through the Nation's roundabouts I discovered at least one that contains
segments that curve in the opposite sense to the overall direction of
the roundabout - the thing looks like a dog-bone, fat at one end, thin
in the middle and fat at the other end. So you can't automatically
reverse segments that look wrong.

Quite often, people tag ways that obviously are not parts of a
roundabout with junction=roundabout and these warnings should find about
50% of those!



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