3D projection is a projection technique in which the images and videos are displayed spatially. It works with two projectors that display two slightly offset images, one for the left eye and the other for the right eye.
The technique of 3D projection starts from the recording technology, which works with 3D cameras. This can be two cameras or a stereo camera, which has two lenses at eye distance, through which the perspective differences are recorded. The projection is done with two projectors that project the two images onto a screen. In VR headsets, the two images for the left and right eyes are shown by two small displays located a short distance in front of the viewer's eyes.
In order to obtain a spatial impression with the projection technique, the two images for the left and right eyes are offset and polarized differently using polarization filters. The viewer separates the two images with polarization glasses so that the image for the left eye is only transmitted through the left polarization glass, and the image for the right eye is only transmitted through the right polarization glass.
As an alternative to 3D projection with two projectors, there is projection with one projector that sequentially displays the image for the left and right eye. The separation for the viewer can be done by shutter techniques and shutter glasses. For this purpose, the shutter glasses must be synchronized with the image switching.