Title Virtual Reality ? Concepts and tools

This technical and scientific field is referred to by a surprising oxymoron: "virtual reality". This association of two a priori opposed terms is not innocent: is the virtual the opposite of the real? Without getting into a philosophical debate, which is inappropriate here, let's note that the choice between the real and the virtual is one that engineers have to make. For example, during the design phase of a product, the evaluation of the object's qualities can be based on its virtual representation (thanks to a digital model), or on a real prototype. The engineer is often faced with the following dilemma:

• test virtually from a configurable, but perhaps unrealistic, model;

• evaluate a real, but fixed, product.

This is not a new issue. But since the rise of virtual reality techniques, it has become more complex to study, since it involves subjective human criteria. Now that the term "virtual reality" is well-established, we have to take it as it is, with some risks of confusion or misunderstanding, which we shall endeavor to dispel in this article. It is advisable to clearly define the field it covers, and to present its main professional applications, the objective of the first part.

In the second part, we propose a theoretical model of immersion and interaction, for a user of a virtual reality system.

The third section presents the main commercially available sensory-motor interfaces, classified according to the senses or motor responses called upon.

In the fourth section, we outline the main difficulties involved in using behavioral interfaces: technical, psychophysical, ergonomic and psychological.

The fifth part of this article deals with models and tools for creating a virtual environment, defined as the computerized description of the synthetic world in which the user(s) evolve(s). The aim is to use computer tools to represent a world that more or less faithfully reproduces the reality of objects' shape, appearance or mobility.

We then find computer models, at different levels of abstraction, for the development of virtual reality applications. These include :

• computer models dedicated to the representation and realism of the objects and entities represented;

• geometric models ;

  illumination models ;

  synthetic human models at a higher level of abstraction.

Finally, the technical implementation of a virtual reality simulation calls on specific software tools, the particular features of which are described...