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Inventors at MIT are developing a system for tracking human motion and
displaying realistic 3D computer images of how someone is moving (WO 99/53838).
Gyroscopes and accelerometers built into a subject’s clothing transmit signals
that represent relative movement of the body, arms and legs. To get an accurate
fix on where the body is in a room, MIT puts ultrasonic beacons on the ceiling
to send out time-coded pulses. Sensors on the clothing pick up the code from
overhead beacons, and use it to triangulate their position. To avoid confusing
the ultrasound sensors with signals from too many beacons, the clothing is
fitted with infrared pulse emitters, and the beacons only switch on when they
detect infrared from directly beneath them.