[Tagging] Tunnels and bridges

[Tobias Knerr]

On 31.01.2013 17:31, Janko Mihelić wrote:
> I read a bit about 3D buildings, and it's pretty compatible. Here is an
> article about simple 3D buildings:
> 
> http://wiki.openstreetmap.org/wiki/Simple_3D_Buildings

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.

While you could probably model a crude bridge shape with building:part,
I would not have imagined that they would be used for bridges. Maybe
it's possible, but they were designed as volume shapes. That is, as
"blocks" where the interesting stuff is inside, rather than on top.

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'm wondering whether the approach you describe has some merit
nevertheless - because after all, many bridges do incorporate towers or
other building structures - but I feel it should not be used as the
primary approach to modelling bridges.

> We should agree what to do with the height (and min_height) of the
> building=bridge area. If it goes over uneven terrain, there is no unique
> height.

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.

Tobias