Optimization of CG Models - An Introduction to Computer Graphics for Artists - page 102

Fig. 8.2 In this model, three triangles are hidden behind the blue triangle and may safely be
removed

When working with open geometry, take care to check whether openings not
visible to the camera have an effect on scene lighting, shadows, or refl ections.
Depending how the scene is lit, you may have to build more geometry because of
the way hidden portions of the model interact with the environment.

8.4 Curvature Detail

Curvature detail , as distinct from curve resolution, is a description of the angle
threshold before a new segment is introduced to represent a curve. If a 360°
circle is divided into 16 sections, the distance between each vertex pair is 22.5°,
but the angle between each edge pair is 157.5°. The threshold for inclusion is at
least 157.5°.
Architectural models are often built of polygons that are positioned at sharp
angles to each other, usually right angles. The angles of an architectural subject are
often sharp, or acute (Fig. 8.3 ). An acute angle is 90° or less. An obtuse angle is any
angle greater than 90°. Acute angles are a poor subject for curvature detail-based
optimization because elimination of acute angles removes detail that is often critical
to the likeness of the subject. When an architectural subject has curvature, it is usu-
ally single-axis segmented curvature. This means it has already been optimized to at
least a limited extent by the designer of the building, and remains a poor prospect
for curve detail optimization.
More promising are organic subjects, or CAD designed objects like cars, planes,
vacuum cleaners, and anything else built predominantly of curves. This class of
objects will have many obtuse angles between edges. Many of these can be eliminated.