Dear all,
Thank you for your valuable answers and sorry for my delay. After checking several stations (Munich, Karlsruhe, Nuremberg, Frankfurt, Hamburg) and shunting yards (Nuremberg, Maschen) I would like to add some further remarks.
Am 20.09.2016 um 21:57 schrieb Roland Hieber:
On 19.09.2016 19:02, Denis Stein wrote:
P1. Proposals for the position of tags for single turnouts (abbreviation: ST; including both straight as well as curved ones): P1(a) Tip of the switch blade (i.e., the position where the route changes; might be also recognized by the point machine in aerial images) P1(b) Tip of the frog ("massif" part; can be approximated from the intersection of both inner rails) P1(c) another proposal?
P2. Proposals for the position of tags for diamond crossings (abbreviation: DC): P2(a) Center of DC, i.e. intersection of both track centerlines P2(b) another proposal?
P3. Proposals for tagging of complex switches: P3.1 Decompose them whenever applicable: - diamond crossing with ... slips: * single = 2x ST + 1x DC * double = 4x ST + 1x DC - three-way switch = 2x ST
Especially to Michael: Yes, "three_way" equals Doppelweiche in German, but seems to be used not that much [1, 2].
(solves also the route ambiguity problem in single slip case)P3.2 Tag those parts according to P1 and P2.
_My favorite_ is: P1(a) + P2(a) + P3.1 + P3.2, which considers the position of turnouts and diamond crossing and clearly defines the drivable routes on them clearly.
Yes, that is what I tagged in the past and it's also my favourite because it's suited best for routing purposes as well as collision detection (in conjunction with track gauge). Especially because for roads we also tag the centerline, so there is the principle of least surprise, and algorithms can be reused for railways.
I fully agree. This decomposition of switches is quite often used in Karlsruhe, but most of the other above mentioned places are not yet tagged like this (feel free to ask me for a detailed list of node-IDs; I checked especially "single_slip" (einfache Kreuzungsweiche)).
Am 20.09.2016 um 16:23 schrieb Michael Reichert:
I prefer to map single and double slips like diamond crossings but with special tags. If we want to map the possible turnout directions of single slips, I would use turn restriction relations as used on roads. Routing engines have been supporting turn restrictions for many years. To reduce the number of turn restrictions which have to have mapped, I would not map a relations if it is just the opposite of another turn restriction on that point (i.e. copy of another relation but from and to members are switched).
Using one node for the whole switch might be ok. However, there are only 280 nodes tagged as "single_slip" [3]. Unfortunately, turn restrictions are -- considering the seven places mentioned above -- only used in Karlsruhe (feel free to ask me for a detailed list of singe_slip node-IDs and a comprehensive overview on single/double_slip nodes in Karlsruhe). Thus, tagging one node as "single_slip" is fine. The ideal solution would be a decomposition in three nodes as previously proposed which in turn avoids the use of turn restrictions.
While writing a routing engine for trains becomes easier if we map single/double slips as simple points, rendering a nice map (especially track layout diagrams becomes more difficult) becomes more difficult. There are several OSM-based routing engines which already support turn restrictions but there is no software which simplifies double slip points mapped in a way you propose. (In general, cartographic generalization of geospatial data beyond a simplification of the geometry is more difficult than parsing turn restrictions)
In my opinion, there is no need for a automatic decomposition in a routing engine etc. My proposal considers only (future) "tagging guidelines".
Off-topic: Are there any (OSM-based) routing engines for railway vehicles?
Kind regards,
Denis.
[1] https://taginfo.openstreetmap.org/keys/railway%3Aswitch
[2] https://taginfo.openstreetmap.org/search?q=railway%3Aswitch%3Dthree_way
[3] https://taginfo.openstreetmap.org/search?q=railway%3Aswitch%3Dsingle_slip