To allow for a realistic display of complex visualisation and virtual worlds are variety of different technologies is used.
Different factors can affect depth perception. Examples would be perspective, motion parallax, shadows or depth of field. To perceive a real 3D impression in virtual environments, the scene has to be displayed from a slightly different perspective for the right eye and the left eye.
These systems display alternating images for the right eye and the left eye. Typically this happens with twice the normal display frequency. So called shutter glasses are used to separate the images for the left and right eye. Inside the shutter glasses an LCD is able to close one side of the glasses and open the other one. This happens in rapid succession (thus active stereo). If an image for the right eye is displayed, the left side of the glasses is shut. The synchronisation of the shutting is realised by infrared or radio signals.
This type of stereo is considered passive, because the stereoscopic impression is generated by filters, which are set up in a fixed way. The quality of image separation depends on the quality of the filters. Typical filters are linear or circular polarisation filters, which are used in the projection system and the glasses.
To gain information about the user's posture and position in the physical environment position tracking systems are utilised. Typically a head sensor or marker and an input device equipped with a sensor or marker are available in VR installations. The proper display of the graphics depending on the user's perspective is calculated based on the measured transformation of the head sensor or marker. When the user moves or turns his head the perspective of the scene is changed accordingly and the impression of a realistic display is guaranteed. Position tracking of an input device can be used for interaction with the scene. It is possible to point with the tracked input device at an entity in the virtual space, in order to select it and afterwards manipulate it.
This type of tracking system uses a fixed array of infrared emitters, which casts infrared light on the users. The markers of such systems reflect the light. Several infrared cameras observe the tracked area from different positions. They see the markers a light dots, the rest of the image is dark. With this information the application can calculate position and orientation.