3-D measurement of objects in a cylindrical glass water tank with a laser range finder

In this paper, we propose a three-dimensional (3-D) measurement method of objects in liquid with a laser range finder. When applying vision sensors to measuring objects in liquid, we meet the problem of an image distortion. It is caused by the refraction of the light on the boundary between the air and the liquid, and the distorted image brings errors in a triangulation for the range measurement. Our proposed method can measure the accurate 3-D coordinates of objects surfaces in liquid taken for calculating the refraction effect. The effectiveness of the proposed technique is shown through experiments. The accuracy of the 3-D measurement is 0.7 mm for objects located about 250 mm from the laser range finder when considering the refraction of the light, although that is 2.9 mm without the consideration of it.