Polish stadium looks just great but, I think it’s too complicated for map users to edit such objects in osm. And also it’s too complicated for 3d artists to map such objects in osm with rather poor osm 3d instruments. Also there is no way to use textures which might be great for frescoes mosaics and so on.
Of course we can keep 3d model in separate project or data storage, such as wikidata. But it would be great to keep link between osm objects and external 3d models. Also any kind of render which tries to render building:parts and external models need to know, should it render building:part geometry or object’s geometry is covered by external model.
So I’ve tried to create proposal for link between osm objects and external 3d models. http://wiki.openstreetmap.org/wiki/Relation_3D:Model
Such approach allow you to specify different models, with different level of details for objects. Also it allows you to reuse one typical model for different osm objects.
I don’t know which format is better for architectural models, so this question is out of scope of this proposal. So, what you guys think about this?