A calibration method for non-overlapping cameras based on mirrored absolute phase target

Abstract

Non-overlapping cameras are widely applied in visual measurement system and mobile robotics. The inspection accuracy and performance of the systems highly depend on the calibration accuracy. A novel method for the calibration of non-overlapping cameras is proposed in this paper. A LCD screen is used as a phase target to display two groups of orthogonal phase-shifted sinusoidal patterns during the calibration process. Through a mirror reflection, the phase target is captured by the cameras respectively. The relations between each camera and the phase target can be obtained according the proposed algorithm. Then, the relation between the cameras can be calculated by treating the phase target as an intermediate value. The proposed method is more flexible than a conventional mirror-based approach, because it does not require the common identification points and is robust to out-of-focus images. Both simulation work and experimental results show the proposed calibration method has a good result in calibrating a non-overlapping cameras system. The calibration accuracy can reach 0.2 mm and 0.007° in translations and rotation respectively. A stereo deflectometry system is calculated based on the proposed calibration method. The global measurement accuracy of a standard concave mirror measured by the system can reach 96.8 nm.