Three principles in stereo vision

The fundamental ideas underlying various methods for measuring the positions of three-dimensional target points from multiple images are classified into three principles. The most popular principle is triangulation, which is available when the following two conditions are fulfilled: the relative positions among the view points are known and the directions from the view points to the targets are known. Sometimes, even if one of these two conditions is not satisfied, the target positions can still be measured. Thus we have two more principles: one works when the first condition is fulfilled, and the other works when the second condition is fulfilled. All three principles together with their variations are investigated.