A head-mounted projective display (HMPD) consists of a pair of miniature projection lenses, beam splitters, and displays mounted on the helmet and retro-reflective sheeting materials placed strategically in the environment. It has been recently proposed as an alternative to existing 3D visualization devices. In this paper, we first briefly review the HMPD technology, including its featured capabilities and the recent development in both display implementations and applications. Then the

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... tation of a testbed, namely "playing 'GO' game with a remote opponent in a 3D augmented environment," is described. The testbed not only demonstrates the capabilities of virtual-real augmentation and registration, natural occlusion of virtual objects by real, interaction with augmented environments, as well as networking collaboration, but also embodies part of our long-term objective to develop a collaborative framework in 3D augmented environments. Through the testbed, major calibration issues, such as accommodation/convergence considerations and determination of viewing transformations, are studied and discussed in detail. Both calibration methods and results are included, which are applicable to other applications. Finally, experimental results of the testbed implementation are presented.