Ken,
Bear with me for a moment, as I try to explain.
If you look at the drawing attached you will see that the different "planes" are highlighted. Normal is highlighted on top of the cube. And if you were to construct a cylinder in the "normal x-y" plane, it would start at say x0,y0z0 and extend up or down from there,(depending on your height value was pos or neg).
Keep this picture in your head.
So you could say that the x-y plane is a blanket that cover the x and y axis, but has no value in z. Does that make sense?
Now look at the drawing at x-z plane, the front of the cube is highlighted. So if you were to construct a cylinder in this plane it would start at say x0,y0,z0 and extend y plus or y negative (towards you or away from you).
So you could say that x-z plane is a blanket that covers x axis and z axis with no value in y.
Now I' m confused.
