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[Occams Razer]

I don't recall when or where, but I seem to remember a developer saying that global tunnel (and possibly bridge) support was not currently possible, due to the limitations in the data provided by publicly available mapping services, such as OSM. This is understandable: road map services are only concerned with which roads connect to which other roads and where they are. They typically aren't concerned with how high above or below the natural ground a road is, so the data being used is bound to be incomplete.

Asking a community of a few dozen people to map each and every bridge and tunnel around the world is an unrealistic request, but asking for some fairly quick data and/or brief research from even just a few users could help to make the world just that little bit more immersive pretty easily. This should, of course, be a last-ditch option should more procedural options fall short, but I do think it should remain an option.

[cameni]

Yeah the OSM data are problematic, even though there is supposed to be an information about the height of roads/bridges/overpasses in the form of a layer id, it's very unreliable, to the point that we had to disregard it in our tests when trying to reconstruct the topology of overpasses and bridges.

Tunnels and bridges alone aren't actually that problematic, as long as we can determine the approximate height of the endpoints, which we sometimes cannot guess correctly from the coarser elevation data. Fitting the rest of the junctions is a bit of a challenge.