On Friday 07 August 2009 12:29:09 Marc Schütz wrote: > > On Friday 31 July 2009 17:25:19 Richard Mann wrote: > > > I saw some strange rendering effects when a side road was straight onto > > > > a > > > > > bridge. The bridge was layer=1, so the side road was rendered on top of > > > > the > > > > > main road. That's why all the ways approaching a junction should be on > > > > the > > > > > same layer. You can either achieve this by inserting a short way > > > between the bridge and the junction, or by altering the layer of the > > > thing that > > > > is > > > > > bridged (ie making the stream layer=-1) > > > > Recently we have been discussing this problem on the Dutch talk list > > regarding > > bridges. Keepright doesn't like T-juntions with different layers and > > tags these as 'not so obvious' errors. > > > > The reasoning that we map the centre of the road is faulty. That > > reasoning implies that we need to split up the road because the sidewalk > > does not either continue to the centre of the crossing road. > > +1 > > It was always my view that the way is simply an abstraction of the entire > road, not only its centre. > > > Adding a little piece of road so the junction can be on one layer just > > does > > not make sense. In Amsterdam there are lots of bridges and canals. > > The canals there are physically not on the same layer as the road and > > bridges. > > But for practical reasons we only add layer tags where ways cross without > > connecting (bridge over water). This 'T-junction rule' is causing just > > about > > every bridge to have small extra bits added. Or have roads that do not > > cross > > anything tagged as layer=1. > > On the discussion list the argument is made that we don't need a layer I meant discussion "page" by the way: http://wiki.openstreetmap.org/wiki/Talk:Key:tunnel#Layer > > tag for > > bridges and tunnel (except of course when there are more than two ways > > above/under each other) and I agree with that. So simply removing the > > layer > > tag on most tunnels and bridges would resolve the layer issue. However I > > am > > not sure if it is generally accepted that it is wrong to tag a bridge or > > tunnel with a layer attribute. > > Please don't do that. O.k. I won't. I have no problem with explicitly tagging the layer and have always done so by the way.
> On the wiki (and the mailing lists) there are also > strong arguments against implied layer. Layer should be kept as simple as > it can be, and this also means keeping it as an independent feature that > doesn't change its default value depending on other tags. Also I am also not sure that removing the layer tags would actually 'resolve' the 'T-junction layer issue' since Keepright or whatever system will probably regard the implied layer no differently from a separate layer tag. Lambert Carsten _______________________________________________ talk mailing list talk@openstreetmap.org http://lists.openstreetmap.org/listinfo/talk
