What can be seen in three dimensions with an uncalibrated stereo rig

1 I n t r o d u c t i o n The problem we address in this paper is that of a machine vision system with two cameras, sometimes called a stereo rig, to which no thro~-dimensional metric information has been made available. The only information at hand is contained in the two images. We assume that this machine vision system is capable, by comparing these two images, of establishing correspondences between them. These correspondences can be based on some measures of similitude, perhaps through some correlation-like process. Anyway, we assume that our system has obtained by some means a number of point correspondences. Each such correspondence, noted (m, m') indicates that the two image points m and m' in the two retinas are very likely to be the images of the same point out there. It is very doubtful