Game Development Reference
In-Depth Information
This chapter makes extensive use of the terms object space and upright
space. If you aren't familiar with these terms, you should flip back to
Section 3.2, where the terms were first introduced.
8.1
What Exactly is “Orientation”?
Before we can begin to discuss how to describe orientation in 3D, let us
first define exactly what it is that we are attempting to describe. The term
orientation is related to other similar terms, such as
•
direction
•
angular displacement
•
rotation.
Intuitively, we know that the “orientation” of an object basically tells us
what direction the object is facing. However, “orientation” is not exactly
the same as “direction.”
For example, a vector has a direction, but not an orientation. The
difference is that when a vector points in a certain direction, you can twist
the vector along its length (see Figure 8.1), and there is no real change
to the vector, since a vector has no thickness or dimension other than its
length.
Figure 8.1
Twisting a vector results in
no appreciable change to
the vector
In contrast to a simple vector, consider an object, such as a jet, facing
a certain direction. If we twist the jet (see
Figure 8.2)
in the same way
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