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
