On 15.06.2013 17:00, Eckhart Wörner wrote: > Hi Rob, > > Am Samstag, 15. Juni 2013, 13:33:24 schrieb Rob Nickerson: >> The next steps with any tag proposal that reaches a hung jury is to read >> through the comments and update the proposal to address the issues raised. >> >> In this case I think the wiki page needs to be clearer about what this tag >> is for (a few photo/aerial image examples would help), and how it differs >> from other tags. > > I don't think the rejection of the proposal is based on missing illustration. > In my eyes, the proposal almost completely misses the underlying problem: > the representation of data in OSM is unsuitable for inferring turn > instructions. > > The closest thing to a junction in OSM right now is a node: if there are three > or more points connected to a node, we call it a junction. > Let's talk a bit about that node: how should we infer routing instructions > from the constellation of ways connected to that node? Should we take the > classification of the road into account? Most OSM routing programs are doing an > exceptionally bad job at this, and yet they are not to blame; since the only > way they are actually able to work is by applying heuristics, and the reason > for that is simple: there are no conventions *at all*. > > The second problem is that a junction is not necessarily node-like at all. > Think about divided highways. Or think about links, and you'll soon realize > that turns can have an extent as well. > > A third aspect of the problem is that even if you are perfectly able to deduce > appropriate turn instructions from the geometry, you may still end up with turn > instructions that differ from what the signs say. Deviating from the signs is > probably not a good idea unless your plan is to confuse the user.
+1 @Rob: Did you ever try to describe the junction with the Lane and Road Attributes [1] ? This scheme should allow to indicate the proper lanes to take the turn from and should solve your motorway example without turn lanes. fly ---- [1] https://josm.openstreetmap.de/wiki/Styles/Lane_and_Road_Attributes _______________________________________________ Tagging mailing list Tagging@openstreetmap.org http://lists.openstreetmap.org/listinfo/tagging
