[OSM-talk] Bridges

[Etienne]

Baz
It takes a bit of thought to understand how to make complex intersections
with lots of layers.

The basic rule is that if one feature meets another feature that is on a
different layer then there will be a line between them.  This make sense
because literally you cannot travel from one layer to another - there is no
route.

There is one exception to this rule.  If two ways abutt then there will be
no join.  So if a way at layer 0 abutts another way that is at layer 1 then
there will be no visible join.  Effectively the two ways are on a slope that
transitions from one layer to another.

With these rules in mind the place to transition from one layer to another
is somewhere along the exit ramps from the motorway up to the roundabout.
Sadly this means making more ways than you really ought to need, but that is
the way it is.

It is all explained here:
http://wiki.openstreetmap.org/index.php/Osmarender#Layers although the
description it is somewhat terse and lacks any real world examples.

Etienne


On 10/18/06, Barry Crabtree <barry.crabtree at gmail.com> wrote:
>
>
>
> On 10/17/06, Etienne <80n80n at gmail.com> wrote:
> >
> > Currently Osmarender needs to be explicitly instructed about what should
> > be drawn over what using the layer tag.  There are no plans to infer this
> > from a bridge=yes tag.
>
>
> Thanks - I'm pretty new to this and trying to get it all clear! Am I right
> in assuming that the bridge=yes tag will allow it to be rendered
> differently, and as you say, use the the layer tag to get the appropriate
> ordering.
>
> I've been trying to create a good example for this based on a roundabout
> that goes over a dual carriagway, but can't seem to get it to render nicely.
> If I make the roundabout a way and tag it level=1 it renders it nicely above
> the dual carriageway, but all the junctions with the sliproads have lines
> accross them. I tried splitting the roundabout into four separate ways, and
> just tagged the parts that go over the dual carriagway level=1 and got a
> different looking version that put round caps on the parts at level=1.
> Neither looks right to me.
>
> You can see what has happened at
> http://wiki.openstreetmap.org/index.php/Talk:Editing_Standards_and_Conventions
>
> This was rendered with osmarender 3.1
>
> Cheers. Baz.
>
>
> Etienne
> >
> >
> > On 10/17/06, Barry Crabtree <barry.crabtree at gmail.com> wrote:
> > >
> > > Hi,
> > >
> > > I've been following this disussion & thought it would be useful to add
> > > a short addition to the wiki in Editing Standards and Conventions..
> > >
> > > Bridges:
> > >
> > > If the bridge can be represented as a node (say a small footbridge
> > > over a stream), then it would be tagged:
> > >  highway=bridge
> > >
> > > If the bridge is part of a way, then tag the '''segment''' that is the
> > > bridge as:
> > >  bridge=yes
> > >
> > > If the bridge is a way in its own right, then tag the way as:
> > >  highway=<whatever-type-of-highway-it-is>
> > >  bridge=yes
> > >  name=<whatever-its-name-might-be>
> > >
> > > This gives the renderer enough information to render it properly (draw
> > > it on top of the road, put 'bridge' markings round it etc.).
> > >
> > > I tried rendering a couple of examples with this tagging scheme using
> > > osmarender, but realised it doesn't seem to have any rules for rendering
> > > bridges so they all come out the same.
> > >
> > > This is a very terse summary of what came out of the disccussion on
> > > bridges<http://lists.openstreetmap.org/pipermail/talk/2006-October/008047.html>
> > >
> > > I've put this in the discussion page for now at: http://wiki.openstreetmap.org/index.php/Talk:Editing_Standards_and_Conventions
> > > & if it seems ok will move it over.
> > >
> > > Cheers. Baz.
> > >
> > >
> > > On 10/16/06, Dave <osm.list at randomjunk.co.uk> wrote:
> > > >
> > > >
> > > > > I just feal there is no point going to the troubles of having a
> > > > differnt tag
> > > > > for each feature, so highway=footway, then bridge=yes, or
> > > > style=yes, or
> > > > > cowstandinginmyway=yes, or statues=yes.  Since only one of these
> > > > things can
> > > > > ever be there at once, (no object can share the same phisicial
> > > > space), So
> > > > > why not therefore just put them all under 1 tag.
> > > > >
> > > >
> > > > This isn't entirely true: you could quite easily find a footbridge
> > > > blocked by a cow ;-).
> > > > In this case the way would need to be marked as both
> > > > cowstandinginmyway
> > > > and bridge.
> > > > These aren't physical objects so much as physical properties of
> > > > objects,
> > > > and the schema needs to be able to cope with multiple properties per
> > > > object.
> > > >
> > > > I'm sure there are plenty of real examples which don't involve cows!
> > > >
> > > >
> > > > _______________________________________________
> > > > talk mailing list
> > > > talk at openstreetmap.org
> > > > http://lists.openstreetmap.org/cgi-bin/mailman/listinfo/talk
> > > >
> > >
> > >
> > >
> > > --
> > > Live as if you were to die tomorrow. Learn as if you were to live
> > > forever.  - Gandhi.
> > > _______________________________________________
> > > talk mailing list
> > > talk at openstreetmap.org
> > > http://lists.openstreetmap.org/cgi-bin/mailman/listinfo/talk
> > >
> > >
> > >
> >
>
>
> --
> Live as if you were to die tomorrow. Learn as if you were to live
> forever.  - Gandhi.
>
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