Fixation and a 180 Degree View Simplify Ego Motion Estimation

Although moving human observers actively fixate their eyes on points in the world, computer vision algorithms designed for the estimation of structure-from-motion or egomotion typically do not make use of this constraint. The main contribution of this work is to precisely specify the form of the optical flow field for a fixating observer. In particular, we show theoretically that the use of a hemispherical (retinal) imaging surface generates an optical flow field of a particularly simple form. The predictions of this theory are tested using the first actual hemispherical lens-camera system in computer vision, involving a 180 degree field of view lens. A further contribution is the finding that the sign of flow at the retinal periphery can be used to predict collisions.