Studies on computer-based perception by vision modelling are described. The visual perception is mathematically modelled where the model receives and interprets visual data from the environment. The perception is defined in probabilistic terms so that it is in the same way quantified. Human visual perception mimicked by means of a computer is an important step in cybernetics as this is, generally speaking, one of the goals of cybernetics. At the same time, the measurement of visual perception is made possible in real-time. From the visual perception, some other derivates of it can be computed. One example is the visual openness which can be used for the movement of an autonomous robot. As to another application, mention may be made to spatial design, in building and construction engineering. The paper describes the novel probabilistic theory of visual perception and investigates various properties of it, via the vision model established. The computer experiments are carried out by means of virtual agent in virtual environment demonstrating the verification of the theoretical considerations being presented. At the same time, experimental studies are presented as to the derivates of visual perception demonstrating the far reaching implications of the studies.