There are two cases of distinct viewpoint which are often treated separately, but have much in common:
There are three intertwined goals:
Here we concentrate on the third point. In particular we will answer the question: given a point in one image, where does the corresponding point in the second image lie? It will be shown that for images of rigid scenes this question can be answered very simply and precisely. There are two cases: first, for images of points on a ``known'' plane, the corresponding point is uniquely determined; second, for any image point the corresponding point is constrained to lie on a line (an epipolar line). In both cases these constraints can be computed from image correspondences directly, without requiring camera calibration.