Hi Clay, Am 04/05/2020 um 20.15 schrieb Clay Smalley: > We've come up with some potential solutions, each of which seems to have > its own drawbacks: > > 1. Sharing nodes between levels, as in the Simple Indoor Tagging schema. > This is the approach IsStatenIsland has taken, with a working example at > the West 4th Street–Washington Square station [2]. > 2. Duplicate nodes with identical positions. > 3. Duplicate nodes, but positions scooched off-center a negligible > distance. This is how I mapped out Grand Central Terminal [3], with the > lower level mapped a foot or so away from where it should be. > > Personally, I'm leaning more towards #2. My qualm with #1 is that it adds > intersections to the two overlapping levels of railways, which I find > misleading. And with #3 I worry that I'm mapping for the renderer.
I recommend option 3 and I strongly recommend not to use option 1. Examples of option 3: Dusseldorf, Germany between Steinstraße/Königsallee and Oststraße https://www.openrailwaymap.org/?lang=null&lat=51.2230429467944&lon=6.78480327129364&zoom=17&style=standard Duisburg, Germany: Hauptbahnhof and König-Heinrich-Platz https://www.openrailwaymap.org/?lang=null&lat=51.43331030240311&lon=6.773768663406372&zoom=16&style=standard Note: The operators of the tram and subway systems in Germany often uses OSM data for routing in cases where safety does not matter. Using the same nodes (like mapping to adjacent landuse polygons) breaks routing because routing engines would allow trains to switch between the levels. Using duplicated nodes at the same location is likely to trigger quality assurance services and therefore mappers trying to "repair" it by merging them. Using two identical geometries in straight sections with nodes at different locations, will likely provoke the same as duplicated nodes. Regarding option 2: GraphHopper assembles its routing graph by relying on the node IDs in OSM. It would not suffer from using this option but I doubt that it is safe for the future. If OSM adopts to drop its 64 bit node IDs in favour of the location (32 bit latitude + 32 bit longitude), such cases will cause difficulties. Best regards Michael (maintainer of a railway map style and routing engine)
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