For many years, and perhaps still today, the Polhemus Fastrak was/is the reference standard for low lag, high accuracy six degrees of freedom (6DOF) tracking. Used extensively to track head mounted displays and data gloves, this magnetic tracker was used in most VPL systems and all the 1rst generation Virtuality systems.
For fun, here’s a video showing how to setup and test a 4 sensor Fastrak.
