there are hundreds of thousands of tourist pictures of the notre dame. Each from a slightly different angle and location on the ground. CV experts at UW had the idea to use these free photos as photogrammetry inputs and estimate a 3d model of notre dame. This requires very intense knowledge of CV because each tourist photo needs to be mapped to a physical location around the building and then used to create a 3d model. This is like a much more complicated version of epipolar reconstruction. I think it’s interesting how this could be applied to virtually any location with enough footage or images. I took a class in cv, but I don’t really understand how enough 2d information can construct a 3d model with lots of math. Now that notre dame has burned down, processes like this allow retroactive 3d models of a a location that can no longer be captured.
https://www.washington.edu/news/2007/11/01/vacation-photos-create-3d-models-of-world-landmarks/