Image ruler and its applications in distance and area measurement

The paper presents a practical measuring system based a CCD camera and two laser projectors Because of the disposition of the laser projectors which are formed in parallel, distance between the projected spots always remains the same. However, the size of the laser-projected spots appearing in CCD image frames will vary according to the photographing distances. Analogue to a physical ruler, the proposed measuring method is therefore named as an image ruler because of its capacity in measuring distance and area via an established relationship between pixel counts and photographing distance. To overcome the problem of laser diffusion of projected spots generally occurred in existing measuring method, center of the projected spots can be accurately identified by a proposed method taking account of video signals of multiple scan lines. As a result, concerns about the diffusion effect of laser rays are also addressed and measurement accuracy is therefore not affected by this adverse effect. Simulation results have demonstrated that satisfactory results can be obtained via the proposed approach.