Image-based system for measuring objects on an oblique plane and its applications in 2-D localization

This paper presents an image-based framework for measuring target objects on an oblique plane by using a single charge-coupled device camera and two laser projectors mounted in parallel beside the camera. Because of the alignment of the laser beams, which form in parallel with the optical axis of the camera, laser-projected spots in the image can be processed to establish relationships between distance and pixel counts of the projected spots in the image. Based on simple geometrical derivations without complex image processing, the proposed approach can successfully measure the photographic distance, the distance between two arbitrary points on the oblique surface, and the incline angle of the oblique surface. Thanks to its ranging capability, the proposed image-based measuring system is further applied to localize objects on a ground surface in addition to depth measurement. To demonstrate the feasibility of the proposed approach for practical applications, we propose a surveillance framework under which a pan-tilt-zoom camera tracks objects in an environment according to the 2-D localization results obtained via the proposed method. Experimental results have demonstrated the effectiveness of the proposed approach in distance measurement, as well as localization of objects on an oblique plane.