[Tagging] Tunnels and bridges

Janko Mihelić janjko at gmail.com
Thu Jan 31 21:05:24 GMT 2013

2013/1/31 Tobias Knerr <osm at tobias-knerr.de>

> I think you are overlooking several problems. To start with,
> building:part cannot do arcing structures - like many bridge decks. They
> can also not easily to structures that become wider or narrower towards
> the top - like some bridge piers.

Anything more complicated than prisms for piers and areas for bridge decks
is not a problem to be solved in openstreetmap IMHO. That is a job for 3D
building models in other databases.

> Also note that "Simple 3D Buildings" doesn't have an established
> solution for ways on top of the roof yet. With normal buildings, that's
> a niche use case that would be good for, say, gardens or parking areas
> on the roof. But if you think of bridges as buildings (a style of
> thinking I'm not particularly comfortable with), this is essential, as
> you almost always have highways/railways on top of the "roof" then.

I think that connecting a road with the bridge area (with sharing nodes) is
enough to tell the renderer that a road is on this plane.

For the record, the height of a building mapped according to "Simple 3D
> Buildings" is always based off the point where terrain is the lowest.

I am thinking that this could deserve it's own type=bridge (instead of
type=building) tag for a relation. It would help renderers make unique
rules for rendering bridges. We could put specialized tags on piers like
pier:top=arch, pier:top:width=3, or who knows what else.

Janko Mihelić
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