Positioning sensor by combining photogrammetry, optical projection and a virtual camera model

Abstract

A novel, low cost, non-contact measurement technique is proposed to realize an optical positioning sensor that enables real-time measurement of a small lightweight module's location. The technique is based on a combination of photogrammetry, optical projection and a virtual camera model. The module generates an optical pattern that is observable on the surrounding walls, photogrammetry is used to track the motion of the projected optical pattern, and this indirectly allows the motion of the module to be tracked. This is done by treating the module as a virtual pinhole camera, generating a virtual image that carries the angular characteristics of the optical pattern. Images of the projected optical pattern on the walls taken by cameras around the room, together with the virtual image, are then processed through a photogrammetry-based bundle adjustment. This results in a position and orientation estimate of all cameras, including the virtual pinhole camera. The position and orientation of the virtual camera is therefore also the position and orientation of the module. Both experiment and optical ray-trace simulations are performed to validate the proposed technique. Experimental agreement of 3 parts in 104 was obtained by translating the module over 0.9 m. The incorporation of the virtual camera model is innovative, leads to a simple solution, and is more robust than the previously published approach.