The projective approach to stereo vision investigates what can be done with completely uncalibrated cameras. This is very important, not only because it frees us from the burden of calibration for certain tasks, but also because it provides mathematical background for many aspects of stereo vision and multiple image algebra, such as self calibration techniques.
The subject was perhaps investigated by mathematical photogrammetrists in the 19th century, but if so the results do not seem to have survived. More recently, following an unnoticed paper by Thompson [25] in 1968, work on projective invariants around 1990 and the 1992 projective reconstruction papers of Faugeras [3] and Hartley [9] launched an enormous burst of research in this field.