Game Development Reference
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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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