
216 Virtual Reality: Concepts and Technologies
at a different time for each pair of stereoscopic images sent by the two video projectors.
With eyeglasses having two filters that transmit only the desired image to each eye,
the observer sees the images in relief. With polarising eyeglasses, it is also possible to
look away from the screen without any disturbance. They are lighter than the active
eyeglasses and do not require battery power supply.
Polarisation of images is either a cross polarisation at 90
◦
(which has the lowest
performance and the lowest price for eyeglasses) or a “circular’’ polarisation. The
polarising filters, placed in front of