Calibration with robust use of cheirality by quasi-affine reconstruction of the set of camera projection centres

A method for upgrading a projective reconstruction to metric is presented. The reconstruction is first transformed by considering cheirality so that the convex hull of the set of camera projection centres is the same as in the metric counterpart. The method then proceeds iteratively and starting from such a reconstruction is a necessary condition for many iterative calibration algorithms to converge. The results show that in practice it is also most often sufficient provided that the minimised objective function is a geometrically meaningful quantity. The method has been found extremely reliable for both large and small reconstructions in a large number of experiments on real data. When subjected to the common degeneracy of little or no rotation between the views, the method still yields a very reasonable member of the family of possible solutions. Furthermore, the method is very fast and therefore suitable for the purpose of viewing reconstructions.