Virtual reality (VR) is an artificial, non-existent in nature world in which a person can be fully “immersed” not only as an observer, but also as a participant. Virtual reality systems are technical devices and software that create the illusion of human presence in this artificial world and, in some cases, allow to manipulate its objects.

Most all virtual reality systems have (at least, should have), the following basic characteristics

Real-time simulation. The virtual reality system should give the user in response to the actions performed a picture, sound, as well as a set of tactile and other sensations (if any are provided) instantly, without noticeable delay.
Realistic imitation of the user’s environment. To fully immerse the user in the world of virtual reality, the system must display virtual objects with a high degree of realism, so that they look “live”.

Support for one or more users. Virtual reality systems are differentiated by the number of simultaneous users and are divided into individual and collective. As a rule, individual systems are created on the basis of display devices with which only one person can work (helmets, glasses, etc.). Systems for collective work are created on the basis of display devices available to several users at once. An example is a stereoscopic video projector, which forms a three-dimensional image on a large screen.

VR-system should give a stereoscopic image, which provides a sense of depth of space. A person has binocular vision, i.e. perceives the world with both eyes at once. The images seen by each eye are slightly different and not three-dimensional separately, but our brain combines the two images into a single three-dimensional image.

Modern technologies for generating pseudo-dimensional images are based on this effect, and the so-called stereoscopic image pairs are created, providing the illusion of volume.
Interactivity is the possibility of interaction with the virtual world. In the “virtual universe” the user must be an active observer only. He must be able to interact with the virtual environment, and it in turn will rely on the user’s actions. This will allow the user to look around and move in any direction within the virtual environment.