In addition to trhway's answer, I'd say we use a lot of assumptions about the world : houses usually have flat, orthogonal walls, streets are flat, etc.. Of cou

In addition to trhway's answer, I'd say we use a lot of assumptions about the world : houses usually have flat, orthogonal walls, streets are flat, etc.. Of course, we can have the computer learn those assumption, but it's more complicated than pure dense stereo.