Seems to me Model.boundingSphere computation is incorrect. For example it can be seen when all model’s meshes (vertices) are moved far away from the coordinate origin in one direction.
Just in case I attch example file. It is SandCastle CesiumAir model moved along an axis by 300 units (model’s length is about 8 units). Done with SketchUp.
When SandCastle “3D Model” example runs with this model, camera view/behaviour and parameters of boundingSphee become strange.
I think that the situation when vertices of a model are not grouped around the coord. origin is not rare in practice.
300.zip (757 KB)