[Tagging] public_transport=platform rendering on osm-carto

Martin Koppenhoefer dieterdreist at gmail.com
Fri Jun 22 09:35:03 UTC 2018

2018-06-22 11:01 GMT+02:00 Paul Allen <pla16021 at gmail.com>:

> As far as routeing goes, the stop position is important.  When I switch
> between bus/foot I do NOT (in most
> circumstances) walk through the platform itself and there's only a 50%
> chance I will walk past the length of
> the platform.  Platforms are often offset from stop positions, such as
> https://www.google.co.uk/maps/@52.0841293,-4.6605633,3a,75y,
> 333.25h,77.93t/data=!3m6!1e1!3m4!1sC6vWAGH4rcR2EoMfVZcIjQ!
> 2e0!7i13312!8i6656

the platform is (by definition) the place where you go to wait for the
vehicle, so it is needed for routing. The stop_position is the spot where
the vehicle stops, it is not strictly needed for routing (of pedestrians)
but the bus needs to know where to stop (doesn't typically need OSM
navigation to drive his bus though). You can deduct the stop_position from
the bus_stop / platform position, i.e. it is already implicit, apart from
rare exceptions where there are some meters of fuzziness (i.e. no practical
implications, you wait at the platform and enter the vehicle when it stops,
regardless the precise position). Usually the difference of a bus stopping
behind another bus makes a bigger deviation from the stop position than any
distance from a projected platform node on a highway (i.e. those meters are
all completely insignificant for all practical usecases).

> If I get off the bus there and turn left I don't walk past the platform.
> If I get off and turn right I'd only walk through
> the shelter if there were people blocking the rest of the sidewalk.  I
> know it's only a matter of a metre or so, but
> from a strictly technical perspective the routeing is from the stop
> position, not the platform.

from a strictly technical perspective you have to take into account whether
you leave the bus at the beginning, in the middle or at the end, which is
usually much more than a single meter, and whether the bus stopped at the
stop position or behind one or two other busses, which again makes much
more difference than a meter.

> Even if the underlying mechanics is taken care of by the database engine,
> it takes more CPU and memory to
> find the segment of a highway closest to a platform than to find the
> highway that a node (stop position) is on.

yes, but I have already written about this:  "OSM traditionally values
mapper convenience higher than simplicity of data evaluation."

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