[Talk-ca] Mapping intersections properly - the impact on routing and illegal routing maneuvres

[Marc Provencher]

I recently posted with an open question asking how others map junction nodes
at complex intersections.

Today I was trying to reproduce certain routing errors which I observed
while driving, and was able to cause Mapsource to route me through an
illegal U-turn, because of a misplaced junction node where there shouldn't
be one.

This picture shows the U-turn:
http://provencher.smugmug.com/Other/Misc/IllegalUturn/831296827_sYc5e-X3.jpg

The problem lies with the access ramp,which has a junction node on both ways
of the divided residential road.  And for some reason the routing algorithm
doesn' t consider this a U-turn, even thought the "avoid U-turns"  setting
is enabled.

Actually, the real problem is that the routing algorithm is using these
"connecting ways"  between the two sides of a divided road, to make a
U-turn. I'm not sure if this problem can be resolved easily.

In my attached picture, removing the junction node which I thought was the
problem simply moved the problem to another intersection.

Cheers,

-- 
Marc Provencher
marc at marcprovencher.com
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.openstreetmap.org/pipermail/talk-ca/attachments/20100408/d2cb5ad2/attachment.html>