Fundamentals of 3D Space - Flash 3D: Animation, Interactivity, and Games - page 202

You may be wondering whether it's possible to control the tilt of the path. The answer
is that you can. The expressions
thisObj.x = xc + r * Math.cos(a);
thisObj.y = yc + r * Math.cos(a);
essentially determine the center point and radius of the circular path in the x- and y-
directions. When the radius is the same for both, they contribute equally, and the tilt is
at a 45-degree angle as Figure 6.29 shows. If the radius were 0 for the y-component,
the result would be a horizontal circular path as in Figure 6.23. If the radius were 0 for
the x-component, the result would be a vertical circular path as in Figure 6.28.
To alter the tilt, then, all we have to do is provide different radius sizes for the x- and
y-directions. For example, the expressions
thisObj.x = xc + r * Math.cos(a);
thisObj.y = yc + r * Math.cos(a)/4;
produce the results shown in Figure 6.30. In this example, xzRotation3b.fla , the
vertical contribution to the path is only one-fourth of the horizontal contribution. The
effect here is quite similar in 3D to what we saw with ellipsor.fla in 2D.
Figure 6.30 Tilted circular rotation with horizontal emphasis