Re: [OSM-talk] Bridge relation on way going under?
2011/5/29 Borbus bor...@gmail.com: I think a much more useful application than those suggested already is to identify all of the bridges that cross over a way. It's easy to find all of the ways that go under a way, but what use is that? It's quite important for waterways in general to be able to find every bridge that will be crossing over your path, and it's also necessary if routing for a tall vehicle on roads. yes, but you only have to modify the above query posted by Lennard slightly to get the ways that cross over the way instead of those under the way. There is no need for a relation, and it would not even help to have these relations (because only a subset will be mapped with them, so you still would perform a database check if this information was important to you). cheers, Martin ___ talk mailing list talk@openstreetmap.org http://lists.openstreetmap.org/listinfo/talk
Re: [OSM-talk] Bridge relation on way going under?
I think a much more useful application than those suggested already is to identify all of the bridges that cross over a way. It's easy to find all of the ways that go under a way, but what use is that? It's quite important for waterways in general to be able to find every bridge that will be crossing over your path, and it's also necessary if routing for a tall vehicle on roads. -- Borbus. ___ talk mailing list talk@openstreetmap.org http://lists.openstreetmap.org/listinfo/talk
[OSM-talk] Bridge relation on way going under?
Hi This wiki page: http://wiki.openstreetmap.org/wiki/Relations/Proposed/Bridges_and_Tunnels talks about adding a relation to the way going under the bridge. This statement: allows both the way(s) crossing the structure /and/ those passing under it to be identified (river and most canals bridges only pass /over/ the waterway, and using only the Way tag bridge=yes means that intersection tests would have to be used to determine the bridges; now we can associate the bridges with the waterway as well. is unclear (to me) as to why it's necessary. Why does an intersection test need to be performed; doesn't the 'bridge=' tag define that the two crossing ways are separate? Hope you can clarify it for me. Cheers Dave F. ___ talk mailing list talk@openstreetmap.org http://lists.openstreetmap.org/listinfo/talk
Re: [OSM-talk] Bridge relation on way going under?
Dave F. wrote: http://wiki.openstreetmap.org/wiki/Relations/Proposed/Bridges_and_Tunnels [...] This statement: allows both the way(s) crossing the structure /and/ those passing under it to be identified (river and most canals bridges only pass /over/ the waterway, and using only the Way tag bridge=yes means that intersection tests would have to be used to determine the bridges; now we can associate the bridges with the waterway as well. is unclear (to me) as to why it's necessary. Why does an intersection test need to be performed; doesn't the 'bridge=' tag define that the two crossing ways are separate? Let's say my application needs to answer, for whatever reason[1], the question what ways are below this bridge. If there is no relation, then this is what the application would do: * gather at all the ways around the bridge * find ways that intersect the bridge way, ignoring the third dimension * check the layer on these ways - all ways that intersect the bridge way (in 2D representation!) and have a lower layer are below the bridge. With a relation, these calculations would not be necessary. In my opinion, this is not a reason to use a bridge relation, though. (There /are/ reasons for using a bridge relation, but this is not one of them.) -- Tobias Knerr [1] most programs don't even need to know that. Routers can rely on the convention that there is no connection between ways without a common node, and 2D renderers only need the layer. A group of applications which actually need that information are advanced 3D renderers. ___ talk mailing list talk@openstreetmap.org http://lists.openstreetmap.org/listinfo/talk
Re: [OSM-talk] Bridge relation on way going under?
On 28-5-2011 18:46, Tobias Knerr wrote: With a relation, these calculations would not be necessary. The people that come up with these types of relations seem to forget that spatial data is what OSM is all about. For instance, using the osm2pgsql schema: http://www.openstreetmap.org/browse/way/13884500 Which roads/railways/waterways does this bridge cross? select osm_id,highway,railway,waterway,name from ( select l1.osm_id,l1.highway,l1.railway,l1.waterway,l1.name, case when l1.layer ~ E'^-?[[:digit:]]+(\.[[:digit:]]+)?$' then cast (l1.layer as float) else 0 end as crossing_layer, case when l2.layer ~ E'^-?[[:digit:]]+(\.[[:digit:]]+)?$' then cast (l2.layer as float) else 0 end as bridge_layer from planet_osm_line l1, planet_osm_line l2 where ST_Crosses(l2.way, l1.way) and l2.osm_id = 13884500 and (l1.highway is not null or l1.waterway is not null or l1.railway is not null) ) as foo where crossing_layer bridge_layer; osm_id | highway| railway | waterway | name ---+--+-+--+-- 41050723 | | rail| | 98667698 | | rail| | 25933220 | unclassified | | | Ferdinand Perdieusstraat 71890307 | path | | | Brampad 9923332 | | rail| | Lijn 36 107068083 | residential | | | Brandweg 53085949 | cycleway | | | 25806811 | path | | | Tunnelstraat 22903417 | unclassified | | | Brandenstraat (9 rows) Time: 7.328 ms -- Lennard ___ talk mailing list talk@openstreetmap.org http://lists.openstreetmap.org/listinfo/talk
