it appears that the problem of single/double/dashed lines is neither easy to tag nor easy to use programmatically. In my opinion the easiest way to handle this kind of data is to map turn restrictions.
Here's how OSRM handles U-turns and turn restrictions. Generally, U-turns are forbidden with one exception: At the end of a dead-end street to be able to leave if you place a via point on the street. Apart from that, all turns are allowed if not explicitly forbidden by restrictions. This kind of modeling is also used elsewhere in other commercial routing application (without saying names). This modeling has the advantage that double/single/dashed lines need to be handled only at intersections. IMHO, it is much easier to allow/forbid the turns at intersections explicitly as given by line markings on the ground. Even if we had some nice and easy way to tag those lines, it would not actually save orders of magnitude of data to process. --Dennis Am 18.04.2013 um 02:36 schrieb Martin Koppenhoefer <dieterdre...@gmail.com>: > > > > 2013/4/17 Philip Barnes <p...@trigpoint.me.uk> > > As a matter of interest, in Countries where it is illegal to turn across > a solid line, for there to be a junction without a break in the line? > > > > usually at junctions there are no solid lines, at the most there will be > interrupted lines or no lines at all (or when there are solid lines it would > indeed be forbidden to turn at the junction). > > > I have driven in a lot of European countries and have noticed that there > are gaps in solid lines for every driveway. I have never come across a > situation where a turn is prevented by a line. > > > there are lots of these situations, but there are also lots of interruptions > for driveways, gasstations etc., yes. > > Example crossing out of town where you can't turn: > http://maps.google.de/maps?hl=de&ll=41.349801,13.75293&spn=0.013482,0.027788&t=m&z=16&layer=c&cbll=41.349827,13.753092&panoid=0dBb2Nn9tjfBufqt37g6xw&cbp=12,94.59,,0,23.63 > > > > This proposal would also need routers to understand the law in different > countries. > > > > yes, at least if you wanted to handle also the stranger cases like the UK > which allows turning on single solid lines. In Germany for instance I am not > aware of any difference between a single and a double solid line (I think > usually you get double lines close to situations where one of the double > lines gets dashed, hence allowing crossing the double line only when coming > from this side). > > cheers, > Martin > _______________________________________________ > OSRM-talk mailing list > OSRM-talk@openstreetmap.org > http://lists.openstreetmap.org/listinfo/osrm-talk
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