3D on a screen

How to make someone 'see 3D' on a flat surface like a projection screen?

The basic principle is to make sure that the left and right eye see a different image. If these left and right images are created from the same scene, but with slightly different camera positions, the person will perceive this as one image with depth. If the distance between the camera positions matches the physical distance between the eyes, the 3D seen will appear to have the correct size.

Active or passive

In stereoscopic VR, there are basically two ways of sending different images to the left and right eye from one projection surface:

• Passive (polarized) stereo uses two projectors with different polarizing filters, and glasses with corresponding (polarizing) filters. Each eye now only sees the light coming from one of the projectors. This technique is used in the portable 3D system. As the glasses are quite cheap, passive stereo is the best choice for large audiences, exhibits etcetera. Unfortunately, passive stereo is not well suited for immersive setups like the Cube or Theatre.
• Active stereo projects the left and right images from the same projector, alternating at a high frequency. This technique is used in the Reality Cube and the Reality Theatre.
  The users wears so-called shutter glasses, which contain one LCD 'shutter' screen for each eye. These shutters 'open' (become transparent) and 'close' (go black) alternately, exactly in sync with the projector. This happens at a frequency of around 100 Hz, which is high enough for the user not to notice any flickering. This high projection frequency requires special-purpose projectors, since normal 'office' beamers cannot go beyond 60 Hz. This makes active stereo generally more expensive than passive stereo, but it is much better suited for curved screens, cubes or other multi-screen VR setups.

Wikipedia: stereoscopy

Wikipedia: shutter glasses