Fundamentals of 3D Space - Flash 3D: Animation, Interactivity, and Games - page 198

Figure 6.25 Changing the radius of the circular path
Plane of Circular Motion
The horizontal plane in which the objects have their circular rotation can be raised or
lowered so that the objects are either above the viewer's eye level, straight on and
even with it, or below the viewer's eye level. The location of this plane is determined by
the value of yc . As shown in Figure 6.26, when yc is 0, the position of the objects is at
eye level. As yc increases, the plane moves up and we see more of the bottom of the
objects. When yc has negative values, the planes are below eye level and we see more
of the top of the objects.
Figure 6.26 Changing the vertical center of the circular path