The three-dimensional structure of a scene consisting of at least five points whose images are identified in two perspective views obtained by a translating camera, can be reconstructed up to a 3D affine transformation. Hence, a more detailed reconstruction is possible using less information when compared to the results for arbitrary stereo pairs taken with uncalibrated, perspective cameras.

A family of qualitative methods is described that determines structure of curves in a scene from their image projections in two or more views. For example, plane curves are distinguished from space curves, and space curves from contour generators. The novelty of the approach is that first, it is unaffected by camera intrinsic parameters, so calibration is not required; second, it is also unaffected by camera motion, so viewer motion need not be known; and third, curves need not be matched point by point. Qualitative scene descriptions can be determined using relative measurements, and affine or projective properties alone. The practical power of this family of methods is demonstrated using a real-time vision system based on B-spline snake-tracking.>