[Tagging] public_transport=platform rendering on osm-carto
osm.tagging at thorsten.engler.id.au
osm.tagging at thorsten.engler.id.au
Wed Jun 20 18:43:08 UTC 2018
Everything you write is no different between PTv2 and the old tagging scheme.
FIRST, all the stops, in order. THEN, all the ways that make up the route, in order.
As far as I’m aware, there hasn’t been a route tagging scheme before that mixes the stops into the route before.
The actual PTv2 proposal documents that quite well:
“Each stop is included with two elements (if available): first the <https://wiki.openstreetmap.org/wiki/Tag:public_transport%3Dstop_position> stop_position tagged with role stop and immediately followed by the corresponding <https://wiki.openstreetmap.org/wiki/Tag:public_transport%3Dplatform> platform tagged with role platform. The stops (stop_positions and platforms) should be inserted beginning with the initial stop_position/platform and ending with the terminal stop_position/platform. The ordering of the stop positions in the relation will determine the direction of the route.
After all the stops all the used ways should be inserted into the relation with an empty role. The ways should be inserted beginning with the way at the initial stop position and ending with the way at the terminal stop position.”
I fully agree that the individual pages for tags are a total mess, mixing together information both from previous tagging schemes and PTv2.
When evaluating PTv2 and mapping according to it, the actual accepted proposal (which I linked above) should be considered normative.
If you read through the actual proposal that was accepted, it’s actually pretty clear and well structured.
All the individual pages should probably be cleaned up, and only and clearly contain the information from the PTv2 proposal. That would greatly clear up the confusion people seem to have. But I understand that would greatly upset people that outright reject PTv2 despite it being newest voted on and accepted proposal.
From: Paul Allen <pla16021 at gmail.com>
Sent: Thursday, 21 June 2018 04:21
To: Tag discussion, strategy and related tools <tagging at openstreetmap.org>
Subject: Re: [Tagging] public_transport=platform rendering on osm-carto
On Wed, Jun 20, 2018 at 6:53 PM, <osm.tagging at thorsten.engler.id.au <mailto:osm.tagging at thorsten.engler.id.au> > wrote:
So, valid minimal tagging under PTv2 is very simple:
You have one node (if there is no clear platform) or a way (along the platform edge) or area (the whole platform), which is tagged as public_transport=platform (plus whatever mode of transport is served at the
platform, so bus=yes or tram=yes, or …)
Which all sounds fine, until I try to make sense of the relation. Something (or somebody) seems to like
shoving all platforms at the start of the relation, then the ways in order. Which would work (just) for a routeing
algorithm, if you throw enough CPU at it, but is inefficient. It also gets very confusing when you have a route which is
circuitous and doubles back on part of its earlier route in the same direction, causing some stops to be in the
relation twice. The route I'm thinking of has a stop on that revisited section which is NOT used on the first
traversal but IS used on the second. It's hard to figure out what's going on unless the stops appear in the
relation next to their ways rather than all lumped together at the beginning.
And it gets worse. Suppose I have a simple route, from X to Z with a stop at Y.
X --- bat street --- o --- cat street --- o --- dog street --- Z
X is at the start of bat street, Z is at the end of dog street. Y is in the middle of cat street, not at either of its
junctions with the other two streets.
The choices I have for relation ordering (I'm still learning/battling JOSM to do it) are X, Y, Z, bat street, cat street,
dog street; or X (which appears to be how it's ordered by default), bat street, Y, cat street, dog street, Z;
or X, bat street, cat street, Y, dog street. None of which make it clear to a mapper or consumer what the reality is
without also looking at the map (simple inspection of the data is not enough). Or should cat street be split at Y
so I can have X, bat street, cat street 1, Y, cat street 2, dog street, Z?
Or does it simply not matter where the stops appear in the relation? If not, does it even matter what order they're
in? I would have thought that for efficiency of routeing you'd NEED stop positions on highways too, otherwise
there's an extra search outwards from the platform until it finds the way. Oh, and the nearest portion of the
way may not actually be reachable from the platform because of obstacles.
I'm confused. The wiki doesn't seem to make it clear and nor do the tools. Am I entirely missing the point?
I would appreciate somebody with a deep understanding of this stuff clarifying matters, here or on the wiki.
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