On Sat, Aug 8, 2009 at 8:51 AM, Martin Koppenhoefer<dieterdre...@gmail.com> wrote: > 2009/8/8 Roy Wallace <waldo000...@gmail.com>: >> Forget about the renderer for a second. IMHO we should tag what is on >> the ground. As the wiki says, layer is "used to mark if a >> way/node/area is above or under another one", where "is above or >> under" clearly refers to the physical reality. It's not *physically* >> possible to have something on layer=0 connected at a T-junction to >> something on layer=1 - or at least, > > you will have this situation on all ways with layers: they are > somewhere connected to another way on a different layer. Forget about > the T-junctions for a moment: a simple way with a bridge will have > layer=1 on the bridge, thus the way with layer=0 (before the bridge) > is connected to the way with layer=1 where the bridge begins and ends. > It's always like this. Therefore the convention is: if objects on > different layers share a node, then they are connected at that node. > >> Alternatively, perhaps you are suggesting the layer=* tag should be >> used only to tell the renderer which ways to display on top of other >> ways? > > Not just the renderer. It's a way to model the (relative) spacial > situation into our generally 2D-Database. >> If so, I don't like this because it's clearly tagging for the >> renderer. > > no, it's not, it's about relative order in the db.
Fair enough. In other words, at any node which is a junction of way segments with different layers (whether the segments are part of the same way or different ways), the physical implication is that the slope of the way changes in the close vicinity of that node. I think this would then allow for layer transitions at T-junctions. _______________________________________________ talk mailing list talk@openstreetmap.org http://lists.openstreetmap.org/listinfo/talk
