Estimating the pose of the camera (virtual or real), in which some augmentation takes place, is the most important part of an AR system. This estimation process is usually called tracking1. Many different tracking methods are available (see [7, 14, 2] for review of tracking systems for aug- mented reality and [4] for a review of tracking sys- tems in general) including mechanical, magnetic, ultrasound, inertial, vision-based, and hybrid sys- tems that try to combine the advantages of two or more technologies.