On 22 Jun 2009, at 12:53, Richard Mann wrote:
On Roger's point about sidings - I'd map those as a separate track
group, since they are the sorts of things people would expect to
disappear at lower zooms. So north of Oxford station, I'd have the 4
down carriage sidings as one group, the four running lines as one
group and the 4 up carriage sidings as a third group. Within each of
those three groups, you could either do the individual tracks (as
1of4), or the tracks as a group (tracks=4).
On loops, I'd probably exclude them from the running lines group,
and use other tags (perhaps has_loops=yes) to tell me that there are
extra tracks for a short-distance. You might also do has_loops:left
and has_loops:right, but one-sided rendering is on the tricky side.
So just south of Oxford at Kennington, you'd have the two running
lines as tracks=2 (or 2xtracks=1of2) with has_loops=yes. If I had
done the two tracks separately, the renderer would be entitled to
expect me to have done the freight loops separately as well, so they
can ignore has_loops=yes at high zooms, and just render the ways
that have been drawn.
Can I suggest that as a start you create the detailed track layout and
then we can look at different grouping strategies and see which ones
the Mapnik people and routing people will find useful. Whatever you do
should work for rail and trams and I see no reason for there not to be
generality with roads. Lets not worry too much about the wrapping
until we have stuff to wrap.
For your interest, here is an example road interchange which can be
rendered as a dot if required, or used in driving instructions as
'turn left at the 'Whitehouse Junction'.
http://www.openstreetmap.org/browse/relation/2470
Here is a dual-carriageway example - just bind all the parallel ways
together and a renderer can then do a line down the middle at some
point.
http://www.openstreetmap.org/browse/relation/2490
Here is a railway station where all the elements (including tracks,
sidings, platforms, buildings, car parking, taxi ranks and cycle
racks) are all part of a relation.
http://www.openstreetmap.org/browse/relation/2522
And here is a sample rail junction wrapped up using a relation:-
http://www.openstreetmap.org/browse/relation/162263
This should make it very easy for a renderer. The general rule is 'if
you can't fit in all the detail on the map and it is part of a
relation then do a single dot or single line for the whole thing.
Regards,
Peter
Richard
On Mon, Jun 22, 2009 at 10:45 AM, Roger Slevin
<[email protected]> wrote:
As someone who doesn't have the experience of mapping that you all
do, but I
do know something about public transport, I can see how the various
concepts
for single track and double track etc work along straightforward
corridors
(note these must be "tracks" (or maybe some other term) and not
"lines" - as
a "line" in public transport is something completely separate from the
infrastructure) ... but what happens when operational details get more
complicated ... at stations, or near and in depots and sidings? What
happens for passing bays? Does a track have a directionality
associated
with it (even if it is only implied by a national convention of
"driving on
the left/right"... though that will give some issues on the German
border
where operations switch sides) - and what happens when multiple
tracks are
signalled for bi-directional working?
I sense that there is a potential issue here between describing the
physical
infrastructure and describing its functional performance ... and I
am not
sure the boundary has been drawn correctly between the two.
Roger
-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of Peter
Miller
Sent: 22 June 2009 10:31
To: Jochen Topf
Cc: osm
Subject: Re: [Talk-transit] Multiple tracks
On 22 Jun 2009, at 07:51, Jochen Topf wrote:
> On Sun, Jun 21, 2009 at 05:09:35PM +0100, Richard Mann wrote:
>> No, simpler than that:
>>
>> tracks=1 => render a single line at all zooms
>> tracks=2 => render a double line at all zooms
>> tracks=X => render a multiple line with X tracks at all zooms
>> tracks=1ofX => render a single line at high zooms, but render as if
>> tracks=X
>> at medium/low zooms
>
> But then you'd still draw several lines nearly on top of each other
> in medium
> zoom levels which doesn't look good, which was the problem we were
> trying to
> fix?
>
> Anyway, this is a rather specialized trick about rendering the
> number of tracks
> properly. But what if you want to render other attributes. Say one
> of your two
> tracks is an industrial railway, the other a normal passenger
> railway and you
> want to distinguish those types. On medium zoom levels, is this a
> two track
> thing and we loose the type distinction, or do we keep it?
The dual_carriageway and Junction relations would appear to the a good
way of doing such things. I realise that the 'dual carriageway' term
is not right and that other work would be required on the
specifications, however it would seem a better starting point.
http://wiki.openstreetmap.org/wiki/Relations/Proposed/Junctions
http://wiki.openstreetmap.org/wiki/Relations/Proposed/
Dual_carriageways
A group of parallel tracks would be combined using 'dual carriageway'
and then a group short sections of track and nodes can be combined as
a 'Junction'. The render would then have a choice of drawing modes,
either a single line and single point, or multiple lines/points.
Regards,
Peter
>
>
> Jochen
> --
> Jochen Topf [email protected] http://www.remote.org/jochen/
> +49-721-388298
>
>
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