Let's assign some variables to things. In the pan/tilt picture, let the

axis be along the red rod, oriented positively from left to right. Let the

axis be along the blue rod, oriented positively up. By the right-hand rule, then, we must have the

axis be coming out of the picture towards us, and orthogonal to both the previous axes. Let us suppose you have a camera mounted on the red rod. I'm going to assume that, if the pan is at

radians, and the tilt is also at

radians, then the camera would then be pointed straight up, in the

direction. Is all this clear?