A Refractive Stereo Structured-Light 3-D Measurement System for Immersed Object

Optical 3-D shape measurement is crucial in modern medicine, industry, and other areas, where structured-light-based stereo methods are especially popular for their beneficial characteristics of high precision and robustness. Current stereo systems are usually designed without concerning the influence of the medium between the camera and the target object. Not much research is available for an object immersed in a container such as a glass water tank, where water turbidity and light ray refraction should be considered as the measurement accuracy will be significantly reduced due to stereo matching failures and geometric errors introduced by refraction. To address these problems, in this article, we propose a novel optical 3-D measurement system for an object immersed in a glass water tank. By projecting the gray-code structured light for dense correspondences, we propose a refractive stereo triangulation (RST) method by tracing light rays from the camera to the target object. The method can effectively reduce the geometric errors between the measured points and their true positions. An integrated refractive stereo structured-light (RSSL) system was built for measuring objects immersed in a glass water tank. Experimental results verify the effectiveness of the proposed method and the system was tested to be well working for an immersed object under different turbidity conditions.