Calibration approach for structured-light-stripe vision sensor based on the invariance of double cross-ratio

The problem associated with calibrating a structured-light-stripe vision sensor is that the known world points on a calibration target do not normally fall onto the light-stripe plane from the light projector of the vision sensor. Furthermore, usually, only a small number of the world points on the light-stripe plane can be obtained. We propose a novel approach that employs the invariance of double cross-ratio to estimate as many world points on the light-stripe plane as needed to address this problem. Based on the proposed approach, detailed theoretical analyses of the variances of the estimated world points are given as well as the corresponding simulation studies. A calibration target is made according to the proposed approach to provide accurate calibration points. The experiments conducted on a real sensor that consists of a CCD camera and a single-light-stripe-plane laser projector reveal that the proposed calibration approach is of high accuracy and is applicable to many structured-light-based 3-D visual inspection tasks concerning large work pieces. (C) 2003 Society of Photo-Optical Instrumentation Engineers.