On Wed, Jun 20, 2018 at 6:53 PM, <osm.tagg...@thorsten.engler.id.au> wrote:
> So, valid minimal tagging under PTv2 is very simple: > > > > You have one node (if there is no clear platform) or a way (along the > platform edge) or area (the whole platform), which is tagged as > public_transport=platform (plus whatever mode of transport is served at the > > platform, so bus=yes or tram=yes, or …) > Which all sounds fine, until I try to make sense of the relation. Something (or somebody) seems to like shoving all platforms at the start of the relation, then the ways in order. Which would work (just) for a routeing algorithm, if you throw enough CPU at it, but is inefficient. It also gets very confusing when you have a route which is circuitous and doubles back on part of its earlier route in the same direction, causing some stops to be in the relation twice. The route I'm thinking of has a stop on that revisited section which is NOT used on the first traversal but IS used on the second. It's hard to figure out what's going on unless the stops appear in the relation next to their ways rather than all lumped together at the beginning. And it gets worse. Suppose I have a simple route, from X to Z with a stop at Y. X --- bat street --- o --- cat street --- o --- dog street --- Z X is at the start of bat street, Z is at the end of dog street. Y is in the middle of cat street, not at either of its junctions with the other two streets. The choices I have for relation ordering (I'm still learning/battling JOSM to do it) are X, Y, Z, bat street, cat street, dog street; or X (which appears to be how it's ordered by default), bat street, Y, cat street, dog street, Z; or X, bat street, cat street, Y, dog street. None of which make it clear to a mapper or consumer what the reality is without also looking at the map (simple inspection of the data is not enough). Or should cat street be split at Y so I can have X, bat street, cat street 1, Y, cat street 2, dog street, Z? Or does it simply not matter where the stops appear in the relation? If not, does it even matter what order they're in? I would have thought that for efficiency of routeing you'd NEED stop positions on highways too, otherwise there's an extra search outwards from the platform until it finds the way. Oh, and the nearest portion of the way may not actually be reachable from the platform because of obstacles. I'm confused. The wiki doesn't seem to make it clear and nor do the tools. Am I entirely missing the point? Probably. I would appreciate somebody with a deep understanding of this stuff clarifying matters, here or on the wiki. -- Paul
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