<title>Tangible holography: adding synthetic touch to 3D display</title>

Just as we expect holographic technology to become a more pervasive and affordable instrument of information display, so too will high fidelity force-feedback devices. We describe a testbed system which uses both of these technologies to provide simultaneous, coincident visuo- haptic spatial display of a 3D scene. The system provides the user with a stylus to probe a geometric model that is also presented visually in full parallax. The haptics apparatus is a six degree-of-freedom mechanical device with servomotors providing active force display. This device is controlled by a free-running server that simulates static geometric models with tactile and bulk material properties, all under ongoing specification by a client program. The visual display is a full parallax edge-illuminated holographic stereogram with a wide angle of view. Both simulations, haptic and visual, represent the same scene. The haptic and visual displays are carefully scaled and aligned to provide coincident display, and together they permit the user to explore the model's 3D shape, texture and compliance.