Three camera rigs are connected by wiring to a computer. The computer is also connected to a treatment apparatus. A mechanical couch is provided as part of the treatment apparatus such that under the control of the computer the relative positions of the mechanical couch and the treatment apparatus may be varied. The camera rigs obtain video images of a patient lying on the mechanical couch the computer processes these images to generate a three-dimensional model of the surface of the patient which is utilized to position the patient relative to the treatment apparatus.