<div>While we could do it with relations, the dual-carriageway model might not be the best starting point, since I don't think we'll ever need to set railways up for routing programs to use. Nine months in, I can get my head round route relations and turning-restriction relations, but I struggle a bit with the value of relations to group parallel ways - it seems a complexity too far for the purpose (and I don't see much evidence of renderers making use of it to render dual carriageways).</div>
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<div>If tracks are notably more than the standard ~3m between track centres, then map them as single lines (tracks=1), as soon as they diverge. It's the renderers job to smooth the transition from tracks=2 to tracks=1.</div>
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<div>I'd do any pointwork as single lines, switching from 2xtracks=1of2 to 1xtracks=2 at some convenient point away from the junction where track separation is roughly standard (and let the renderer worry about making the transition seamless). Or just ignore pointwork for the moment.</div>
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<div>I think in time, people will map individual tracks separately. But there needs to be the ability to have a single way as a first step (not least to make it backwards-compatible), and not to make it too difficult to add descriptive detail (how many tracks, whether it is electrified, whether it has passenger services, whether it has fast services, whether it has fast/highspeed lines, whether it has freight lines). This is the sort of information that makes sense at low zooms. Separately, you might want to add the services as relations, so you can put together something more akin to the operator's maps, at a higher zoom.</div>
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<div>Richard<br></div>
<div class="gmail_quote">On Mon, Jun 22, 2009 at 10:30 AM, Peter Miller <span dir="ltr"><<a href="mailto:peter.miller@itoworld.com">peter.miller@itoworld.com</a>></span> wrote:<br>
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<div class="h5"><br>On 22 Jun 2009, at 07:51, Jochen Topf wrote:<br><br>
<blockquote class="gmail_quote" style="PADDING-LEFT: 1ex; MARGIN: 0px 0px 0px 0.8ex; BORDER-LEFT: #ccc 1px solid">On Sun, Jun 21, 2009 at 05:09:35PM +0100, Richard Mann wrote:<br>
<blockquote class="gmail_quote" style="PADDING-LEFT: 1ex; MARGIN: 0px 0px 0px 0.8ex; BORDER-LEFT: #ccc 1px solid">No, simpler than that:<br><br>tracks=1 => render a single line at all zooms<br>tracks=2 => render a double line at all zooms<br>
tracks=X => render a multiple line with X tracks at all zooms<br>tracks=1ofX => render a single line at high zooms, but render as if tracks=X<br>at medium/low zooms<br></blockquote><br>But then you'd still draw several lines nearly on top of each other in medium<br>
zoom levels which doesn't look good, which was the problem we were trying to<br>fix?<br><br>Anyway, this is a rather specialized trick about rendering the number of tracks<br>properly. But what if you want to render other attributes. Say one of your two<br>
tracks is an industrial railway, the other a normal passenger railway and you<br>want to distinguish those types. On medium zoom levels, is this a two track<br>thing and we loose the type distinction, or do we keep it?<br>
</blockquote><br></div></div>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.<br>
<br><a href="http://wiki.openstreetmap.org/wiki/Relations/Proposed/Junctions" target="_blank">http://wiki.openstreetmap.org/wiki/Relations/Proposed/Junctions</a><br><a href="http://wiki.openstreetmap.org/wiki/Relations/Proposed/Dual_carriageways" target="_blank">http://wiki.openstreetmap.org/wiki/Relations/Proposed/Dual_carriageways</a><br>
<br>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.<br>
<br><br><br>Regards,<br><font color="#888888"><br><br><br>Peter<br><br><br></font>
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<div class="im"><br><br>Jochen<br>-- <br>Jochen Topf <a href="mailto:jochen@remote.org" target="_blank">jochen@remote.org</a> <a href="http://www.remote.org/jochen/" target="_blank">http://www.remote.org/jochen/</a> +49-721-388298<br>
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