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?