Y. Genc, , F. Souvannavong, C. Akinlar, N. Navab Marker-less Tracking for AR: A Learning-Based Approach IEEE International Symposium on Mixed and Augmented Reality (ISMAR'02), October 2002 (bib)
	Estimating the pose of a camera (virtual or real) in which some augmentation takes place is one of the most important parts of an augmented reality (AR) system. The availability of powerful processors and fast frame grabbers has made the use of vision-based trackers commonplace due to their accuracy as well as flexibility and ease of use. Current vision-based trackers are based on tracking of markers. The use of markers increases robustness and reduces computational requirements. However, their use can be very complicated, as they require maintenance. Direct use of scene features for tracking, therefore, is desirable. To this end, we describe a general system that tracks the position and orientation of a camera observing a scene without visual markers. Our method is based on a two-stage process. In the first stage, a set of features is learned with the help of an external tracking system during use. The second stage uses these learned features for camera tracking when the system in the first stage decides that it is possible to do so. The system is very general so that it can employ any available feature tracking and pose estimation system for learning and tracking. We experimentally demonstrate the viability of the method in real-life examples.
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