[Talk-transit] Vertical Levels (Layers) versus Altitude for stations

Frankie Roberto frankie at frankieroberto.com
Fri Sep 4 07:45:30 BST 2009

Hi Peter,

good stuff, and I agree with your view that we should tag the "human
understandable" levels. I'm not aware how how precisely these map to
the layers tag (I'd always assumed that this was a hint to the
renderer rather that conveying semantic information), however I see
how that would work.

By the way, I think it may be useful to create a separate "railway
stations (in the UK)" project page on the wiki, so that we can easily
see which ones are "done" and to which level of detail.

On 04/09/2009, Peter Miller <peter.miller at itoworld.com> wrote:
> In the absence of a vast building program of new monorails[1] as
> proposed by Bill Ricker, I am beginning to think about mapping some of
> the more complex transport interchanges here in the UK. I am currently
> adding platforms, walkways and steps to the simpler stations that I
> know and am now thinking about more complex ones.
> Bill also talked about the use of the layer tag on some stations on
> the monorail at Disney with the stations at layer 3 and the track at
> layer 2 and I think it would be useful to talk about how we can
> usefully use layer tags for complex interchanges.
> I checked out the IFOPT CEN standard[2] on the subject and found this
> useful section on "Vertical Levels (Layers) versus Altitude" (they
> call them levels, we call them layers btw)
> 1.4.6 Vertical Levels versus Altitude
> Transport interchanges are often complex buildings with many
> interconnected levels. The
> labelling and description of the levels is used in describing stops
> and directions in PT info
> systems and so needs to be part of the Fixed Object model. This LEVEL
> is a distinct concept
> from that of a vertical spatial coordinate in that it is a semantic
> label (for example
> Departures, Basement , Floor 1, etc). Altitude is in effect the z
> coordinate of a POINT.
> I think this useful for us and clarifies that if the station appears
> to be organised on two 'layers' (using OSM terminology) then it
> doesn't matter that in fact one of the layers incorporates an incline
> at one point so that part of 'layer' it is at a different altitude to
> another part. If of course if there is a slope which connects two
> different distinct layers of the station (something which could also
> occur) then we should consider that to be a path between the layers.
> The logic is that when we start mapping more complex 3D stations (and
> other structures) then we shouldn't get too stressed about altitude,
> but should instead divide the place up into human understandable
> layers. This is something that is often done anyway in diagrams that
> describe the layout of stations[3] and ships[4].
> When we come to map this we are going to need an editor that can allow
> us to see only one level at a time, but there is a growing need for
> editors to allow one to focus on one aspect of the data only and avoid
> picking up or modifying features that are out-of-scope anyway so I am
> sure that will come. While being focused on a particular layer then
> any features added would be added at that layer.
> We would also need to consider slope, steps and lifts between layers
> and the situation where a lift only connects some layers but not all
> of them. A lift is currently represented as a single node because it
> is vertical. How does one indicate which layers it connects? How would
> one assign layers to a complex metro station where one can't guess the
> depth of each element - possibly one would have to count steps and
> measure the height of one of them to calculate a depth for each
> platform and therefore assign layers.. but that still does solve the
> problem for escalators.... So, possibly we can be kept occupied even
> without a massive monorail program.
> Fun stuff ;)
> Peter
> [1]
> http://lists.openstreetmap.org/pipermail/talk-transit/2009-September/000593.html
> [2]
> http://en.wikipedia.org/wiki/Identification_of_Fixed_Objects_In_Public_Transport
> [3]
> http://home.wangjianshuo.com/archives/20080105_shanghai_metro_century_avenue_station.htm
> [4] http://www.wildalaskacruises.com/capabilities.htm

Frankie Roberto
Experience Designer, Rattle
0114 2706977

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