Hi Y'all, First: this discussion is a liiittle bit different from my original intention (not that that's a bad thing).
I am trying to use the existing data and come up with a "best interpretation". Since I will use the entire planet file, manual correction of persistent problems is not a short-term viable option. :-( In particular, I expect both under-noding and over-noding. Over-noding: a node connects two ways that cross at different altitudes (as hinted by layer or bridge tags)...this happens in the TIGER imports (since TIGER is topologically integrated before export) so unless users have specifically fixed this, it'll be there...for every single overpass and bridge in the United states. :-) (Since Tiger doesn't include layer information I don't see how anyone could have automatically fixed this...without layers you can't know which nodes are "false".) Under-noding: I don't know how much existing software will fail to intersect two nodes...an artifact of my import is "fixing" all this (which gives me the over-noded case, although I could easily detect this by flagging nodes added by me at intersections). Second: double-decker bridges I think open a bucket of worms: - Do the two layers share the colocated nodes? Is this even legal? - How well do the editing programs let you manage such a beast? - How well do the maps render it? In Boston I see that the double-decker part of I-93 does not overlap itself...in practice such a map would be pretty unreadable so it doesn't surprise me that the data is how it is. So far I think any candidate heuristic I have looked at for building a 3-d network from the data would manage a double-decker road in a reasonably sane way. cheers Ben Apollinaris Schoell wrote: > On Jul 30, 2009, at 8:46 AM, Igor Brejc wrote: > >> Apollinaris Schoell wrote: >>> On 29 Jul 2009, at 22:05 , Igor Brejc wrote: >>> >>>> Karl Newman wrote: >>>>> The topology rules are simple--if the ways share a node, then >>>>> they are >>>>> connected and it is possible to navigate from any of the connected >>>>> ways to another (subject to turn restrictions, etc.) The layer >>>>> tag is >>>>> primarily a hint for renderers for proper display of vertically >>>>> separated features. If the data is otherwise, then it is an error >>>>> and >>>>> should be corrected. >>>>> >>>> Then how do you handle double-decker bridges? >>>> (http://en.wikipedia.org/wiki/Bridge#Double-decker_bridge) >>>> >>> 2 ways with different layer number >>> >> I was asking more about the "sharing/not sharing nodes" stuff >> between those two ways >> > > can't think of a case where they could share a node. only if we start > to map an elevator between the 2 ways. but then osm needs to extend to > a 3d model. mapping 3d with elevation tag might be to simplistic.... > > at the end of the bridge when the 2 ways can merge into one again then > topology rule applies as outlined by Karl > > >> Igor >> >> >> -- >> http://igorbrejc.net >> > > > _______________________________________________ > dev mailing list > [email protected] > http://lists.openstreetmap.org/listinfo/dev > -- Scenery Home Page: http://scenery.x-plane.com/ Scenery blog: http://xplanescenery.blogspot.com/ Plugin SDK: http://www.xsquawkbox.net/xpsdk/ X-Plane Wiki: http://wiki.x-plane.com/ Scenery mailing list: [email protected] Developer mailing list: [email protected] _______________________________________________ dev mailing list [email protected] http://lists.openstreetmap.org/listinfo/dev
