Optimization of CG Models - An Introduction to Computer Graphics for Artists - page 104

Fig. 8.4 From a distance, these extremely low resolution parts read properly as a bicycle seat
because of their correct size relationships to each other

animate. When you consider parts, also consider the difference between parts that
are literally separate objects but grouped together or selection sets of faces that
share vertices.
It is typical for a low-resolution car to be made of a single polyset for the body
and interior, and then grouped parts for tires and steering wheel. In some cases, the
doors, trunk, and hood are also separated for animation. This moving parts only rule
is very common, and you can expect it to be the primary criteria for deciding which
parts may be safely combined and which must remain separate. For a high poly-
count vehicle to be rendered in a fi lm, you would likely have to build a very long list
of parts and then group them together.

8.6 Incised Detail

Incised detail is literally a face or faces that have been carved into existing poly-
gons. The result can be either a texture boundary or a face that is extruded from
within another face or group of faces (Fig. 8.5 ). If the incised face has been
extruded, the extruded element may be detached as its own object and the result-
ing hole eliminated. After this, the extruded part can be grouped back into the
original polyset.
One reason incised face extrusions are used is that any parts extruded from
another are aligned perfectly, but it also causes a higher poly count because the
vertices that defi ne any common edge between the original object and the extruded