In the cow vs. toy cow example, you get a 3D model of a cow, but you don't know its absolute size. If you ALSO know that the cow is 2m long, or 3m away, you can

In the cow vs. toy cow example, you get a 3D model of a cow, but you don't know its absolute size. If you ALSO know that the cow is 2m long, or 3m away, you can infer the scaling factor for the geometry you estimated using pixels and camera intrinsics.