-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Am 18.07.2010 04:52, schrieb Alan Millar: >> http://maps.cloudmade.com/?lat=45.418666&lng=-122.321563&zoom=16&directions=45.41881686582581,-122.32349395751953,45.4324308667588,-122.36778259277344&travel=car&styleId=1 > >> >> A good example of a place where dual carriageways should be used. >>> Notice the double-double yellow lines separating the two >>> directions of traffic. > >> Definately. The road should never have been modeled as only 1 way >> in the first place. The router was absolutely right. The road was >> wrong. > > No, I don't agree; this is not an obvious dual carriageway. > > You CAN turn both left and right leaving the highway; the middle > lane is a left-turn lane in both directions, crossing the opposite > side. You just can't turn left entering the highway.
Why isn´s it? I see a dual-carriageway with oneway-links on both sides and 2 oneway-links in the middle. As all these ways are oneway in reality just connect or don't connect the middle lane to the carriage-way they are crossing if and only if making U-turns using the middle lane is forbidden. Marcus > > An that is just this one crossing. The very next intersection at > > http://nroets.dev.openstreetmap.org/demo/index.html?lat=45.40876&lon=-122.30162&zoom=17 > > > is just a simple meeting of two roads, as are most of the rest of the > crossings as the road heads east. Ok, so turn-restrictions it is. > That doesn't make any more sense to me than adding "no left turn" > in a place where the link approaches at a small angle of a few > degrees and you are supposed to merge left onto the highway. That > may make sense for routing restrictions, but it is going to really > confuse a human map reader. > > Am I really asking something unreasonable of a router that when an > xxxx_link way meets an xxxx way at a very low angle, the router > should know to go forward and not almost reverse? Yes because a) such intersections with very sharp angles exist in many cities and are valid. (I already said that I know real live examples.) b) It is not the place of the routing-algorithm to change the topology of the well defined graph it is routing on. c) Routers don't care for angles or even for any kind of physical location most of the time. Metrics do but most metrics would act incorrect if they where to associate extreme cost with sharp angles. (A shortest route is no longer shortest if it cares about angles, fastest- and fuel-efficient and motorbike-friendly- already have their own set of rules for angles,...) d) You would need to add your heuristic not to one but to ALL our routing-engines and all their routing-algorithms, document them, test them, tune them, make them well-behaved. As opposed to fixing the map. Whould it not be easier to write a trivial tool to search for such sharp angles and offer them to users for checking if a turn-restriction would be apropriate? Maybe even prepare a changeset, so the offered turn-restriction can be added with one click? That´s even less work then changing one and only one router considering the testing and documentation involved as the router still needs to work correctly on all other roads. Marcus -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.9 (GNU/Linux) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org/ iEYEARECAAYFAkxCoj0ACgkQf1hPnk3Z0cQgAQCeKshSgy0jfkSkbK6IZ8V0wgHS MfgAoL1bRkOH6ab3byiABBaAp0u2CTpZ =lN1l -----END PGP SIGNATURE----- _______________________________________________ Routing mailing list [email protected] http://lists.openstreetmap.org/listinfo/routing
