Hello, sinewave85!

This should have been explained to you . . . at some time, by someone.

I know that the formula is : .

But what if one of the direction numbers is zero?

Do you just drop that part of the equation since it is undefined? .No

Suppose the direction contains a zero: .

Believe it or not, we are allowed to write this:

. . . . .

The standard "excuse" is that those denominators are simply "holders"

. . for the components of the direction vector.

So that we are notreallydividing by zero,

. . we're just "storing" the zero there. . .LOL!