Well, Andrews suggestion is a bit problematic. 1. in reality, the motorway_links are a official part of the motorway. Just look at the signs on the side of the motorway_link. Thus, it should be possible to use ref=A15 for example on a motorway_link. 2. a motorway entry would be quite simple for a router, because the prediction would always be correct: the entry always (?) leads to one motorway with one ref 3. when a motorway_link is an exit, it should be possible to use the junction number on this link, for example as junction:ref. Why? a) the next way might be a tertiary road. A routing engine can't predict the correct ref from this tertiary road b) the motorway_link is used to store information on destination, lanes, lanes:extensions etc. It would be illogical to forbid the junction number being used as well. c) it quite often will be impossible for any (present/future) routing engine to always predict the right exit number based on the motorway_junction ref. Imagine a more complicated junction. These may use y-splits where one highway=motorway is split into two highway=motorways. Or one highway=motorway_link is split into two highway=motorway_links. What should the prediction for the junction number be? Left or right? d) following b and c, this also means that the highway=motorway_junction node is pretty useless for a routing engine. Only in simple exit situations it will be sufficient to show the junction number in your navi-app
Bye, Johan ps I have to complement Martin for his work to get pieces of the somewhat messy OSM puzzle sorted out here: I read the Connect 11/2012 magazine which tested several navi-apps, including Skobbler and Navfree. Connect is pretty harsh on them, especially because of routing problems caused by Openstreetmap 2012/10/23 Andrew Errington <[email protected]> > On Tue, 23 Oct 2012 14:47:40 Martin Vonwald (imagic) wrote: > > Hi! > > > > I'm wondering what ref should be used on slip roads/ramps of a motorway > > (not the junction node, but the way tagged with motorway_link). Up to now > > I've seen: * the reference of the junction > > * the reference of the motorway > > * the reference of the junction not in the ref tag but in junction:ref > > * nothing (neither ref nor junction:ref) > > > > In the Wiki (English and German) I couldn't find an answer. > > > > Any opinions/comments/hints are welcome. > > I suggest 'nothing'. > > The ref of the motorway can be inferred by looking at the end of the slip > road > where it connects to the motorway. > > Same for the junction number. > > A little bit of redundancy is good, but if we can reduce what we store > (because it's easy to derive it from somewhere else) then there's no point > in > entering, storing, and maintaining it. > > Best wishes, > > Andrew > > _______________________________________________ > Tagging mailing list > [email protected] > http://lists.openstreetmap.org/listinfo/tagging >
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