Determining Radius and Position of a Sphere from a Single Catadioptric Image

In order to improve robot capabilities related to playing with a flying ball, reliable methods to localize a sphere in the 3D space are needed. When the radius of the sphere is known, it can be localized by analyzing a single, perspective image of it. When the sphere radius is not known, a single perspective image is not sufficient. In this paper we consider axial-symmetric catadioptric cameras, i.e. devices consisting of an axial-symmetric mirror plus a perspective camera, whose viewpoint is on the symmetry axis. If the viewing rays are not all concurrent at a single point, this camera is said to be non-central. We show that, using a noncentral axial-symmetric catadioptric camera, a single image is sufficient to determine both the position of a sphere and its radius. Some preliminary experimental results are also presented.