Greg Welch Gary Bishop Leandra Vicci Stephen Brumback Kurtis Keller D'nardo Colucci The HiBall Tracker: high-performance wide-area tracking for virtual and augmented environments. 1-10 1999 VRST http://doi.acm.org/10.1145/323663.323664 db/conf/vrst/vrst1999.html#WelchBVBKC99