Graphics Reference
In-Depth Information
4.8 Summary
Bounding volumes are simple geometric shapes used to encapsulate one or more
objects of greater geometrical complexity. Most frequently, spheres and boxes are
used as bounding volumes. If a really tight fit is required, slab volumes or convex hulls
may be used. Bounding volumes are used as early overlap rejection tests, before more
expensive tests are performed on the geometry enclosed within them. As discussed in
Section 4.1, there are trade-offs involved in the selection of bounding volume shapes.
By using bounding volumes of tighter fit, the chance of early rejection increases, but
at the same time the bounding volume test becomes more expensive and the storage
requirement for the bounding volume increases. Typically, bounding volumes are
computed in a preprocessing step and, as necessary, transformed with the bounded
objects at runtime to match the objects' movements.
In addition to detailing the most common bounding volumes and how to com-
pute them, this chapter described how to perform homogeneous intersection tests
(between volumes of the same type). These tests were meant as a teaser toward
Chapter 5, which in considerable detail covers (heterogeneous) intersection tests and
distance calculations between primitive geometrical shapes, such as lines and line
segments, spheres, boxes, triangles, polygons, and polyhedra.
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