Hi Christoph, my suggestion was to clearly separate the subject of water flow from the subject of routing. Whether roads are mostly bidirectional or not is irrelevant I think, as routers have to be able to handle one-way roads anyway. If I understand it right, edges in routing graphs are often one-way anyway as the characteristics from A to B may be different from B to A. If you are interested in hydrodynamics on a large scale, like predicting the route an unpowered floating object would take, that is entirely different to the use of a routing engine to suggest a route to the skipper of a boat. Simply adding a way from one side of a lake to the other to stop some QA program complaining is bordering on tagging for the renderer... --colin
On 28 July 2015 11:17:00 CEST, Christoph Hormann <[email protected]> wrote: >On Tuesday 28 July 2015, Colin Smale wrote: >> If we can separate the flow direction discussion from the routing, >> the latter becomes a more generic "routing through areas" problem >> which has been discussed before in the context of pedestrian routing. > >Water flow structure is not only about flow direction of individual >segments, it is also about connectivity - hence the routable network. > >And yes, you can try to take polygons into account to determine >waterflow - you have to at the moment since missing line mapping is >just too widespread. But for non-trivial polygons (i.e. ones with >holes or areas represented by multiple polygons) this is generally >ambiguous and it is hard to analyze as well. > >The analogy between water flow analysis and traffic routing is >misleading here since traffic routes are mostly bidirectional. If you >imagine a road network exclusively built from oneway roads you can >immediately see that having parts of that network represented as >polygons will make routing difficult. > >And - this is even more important - it also makes it difficult to spot >errors in mapping. If you have a full line mapping of a river network >it is very easy to identify problems locally for QA tools or validators > >in editors - just like in case of the coastline. If you rely on >polygon features creating connectivity in the waterflow network you >need to analyze it in full before you are able to spot where mapping is > >broken. > >-- >Christoph Hormann >http://www.imagico.de/ > >_______________________________________________ >talk mailing list >[email protected] >https://lists.openstreetmap.org/listinfo/talk
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