Game Development Reference

In-Depth Information

Figure 14.9
Example of the part modelled by CSG with povray

representation of elementary primitives and the determination of the result of applying

operators to these structures.

In terms of properties, we can say that:

•

the set of objects represented depends essentially on the basic primitives used, but

it can be very vast;

•

The model is suitable for certain calculations but makes it completely impossible

to perform certain operations like a simple volume calculation;

•

The uniqueness is certainly not verified; the order of construction determines the

primitives used and the order of applying the operators;

•

The CSG models are very easy to use and are thus generally implanted in all 3D

modelling tools, even though the internal structure of these tools is similar to

surfaces;

•

The precision and concision of models depend essentially on the primitives used

and their appropriateness to the object to be modelled.

The CSG models are naturally the keystones of mechanical CAD tools in terms

of the ergonomics as well as the production of the objects designed. However, their

suitability for virtual reality is highly debatable as we will see further. In terms of

visual rendering, the CSG is used more in non-real time softwares such as ray tracing

softwares. In fact, ray tracing techniques can avoid explicit calculation of the volume

of the modelled object.

14.3 SURFACE MODELS

We will now discuss surface representation where we will try to model the borders

of the object. For this purpose, surface modelling is also called Brep (Boundary Rep-

resentation). The problem in this case is different as we are determining a surface,

i.e. a two-dimensional object from three-dimensional space. Therefore, it is necessary

to try to represent the boundary surface in a form that can be used for algorithmic

processing. The surface models are classified as per the type of surface used.

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