and, hence, points on this plane project on to image points , which are points on the image -axis. It also follows from that also lies on . Hence is the plane defined by the optical center and the -axis in the image plane.

Similarly, is the plane defined by the optical center and the -axis in the image plane.

Thus unlike , and are dependent on the choice of the coordinate system on the image plane. In particular, the intersection of these two planes is the line joining the optical center with the coordinate origin in the image plane. This line will not, in general, coincide with the principal axis defined below.

Subhashis Banerjee 2008-01-20