The orthogonal projection of the perspective centre on a tilted photograph, is called A. Nadir B. Isocenter C. Principal point D. Plumb point

The correct answer is: C. Principal point

The principal point is the intersection of the optical axis of a camera with the image plane. It is the point on the image plane where the optical axis intersects the image plane perpendicularly. The principal point is used to calculate the focal length of a camera and to correct for lens distortion.

The nadir is the point on the Earth’s surface directly below the observer. The isocenter is

The principal point is the most important point in a camera because it is used to calculate the focal length of the camera and to correct for lens distortion. The nadir, isocenter, and plumb point are not as important as the principal point.