**5. 3D objects and virtualization sequence**

The whole process of object processing and virtualization is called the virtualization sequence. A simplified 3D virtualization sequence scheme is shown in **Figure 8**. Of course, each of these steps contains a number of other sub-steps naturally. Many sub-sequences of this sequence including 3D objects modeling and editing are already standardly used in practice, and they have steady conventions and standards. The virtualization sequence is important in defining and creating VR-based systems. In principle, it determines all the virtual world objects, their way of use, and of course, the semantics (meaning) of individual objects [11].

As mentioned in the chapter, 3D computer modeling is the creation or modification of a 3D graphical virtual model using a specific software tool—3D modeling application (e.g. Blender, Autodesk 3D Studio Max, Maya, Sketchup, etc.). The modeling process of preparing/editing graphical data is similar to sculpture creation. 3D objects modeling is not an exception in this case and it is based on a four-step principle: model/object preparation, polygonal modeling, texture preparation, and texture application and filtering. The properties of these steps depend on the model/ object type. The created model/object can be used for visualization, simulation, or for 3D printing.

Each model consists of *points*, *edges*, and *faces*. These are primitives that create geometry of any model. **Figure 9** represents geometry of wheelchair using primitives.

**Figure 8.** *A simplified 3D virtualization sequence scheme.*

**Figure 9.** *Points, edges, and faces represented on cone model.*

Wheelchair model has assigned base color texture. A number of polygons are in a count necessary to shape the model into a wheelchair look. Although it does not look realistic, it brings a possibility to render such model faster. Therefore, its optimal design solution for VR headsets. All models in wheelchair simulators are designed with low polygons principle. Due to this fact, scenes have united design with fast rendering. As helmets are used commercially, it is generally known that realistic look does not affect the possibility of user being drawn into the environment. The user is drawn into the environment, especially, by united design of models and their texture, interactivity with environment and sound effects. If these elements are designed creatively and are not exaggerated, user can enjoy the virtual world samely as environment with realistic look.
