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.
Highlights
Multiple cameras are applied in visual measurement [1,2,3], scene surveillance [4, 5], and mobile robotics [6,7,8] in case single camera could not satisfy the functional requirement
Pagel et al [6] developed an approach for calibrating non-overlapping cameras with hand-eye calibration (HEC) technique [9]
This paper presents a novel calibration method based on mirrored phase target for non-overlapping cameras
Summary
Multiple cameras are applied in visual measurement [1,2,3], scene surveillance [4, 5], and mobile robotics [6,7,8] in case single camera could not satisfy the functional requirement. Due to the design restrictions and cost savings, the field of view (FOV) of the cameras is unable to be guaranteed overlapped In these cases, the camera parameter and the relative positions of the cameras should be calibrated for a system consisted of non-overlapping cameras. Lamprecht et al [11] calibrated a non-overlapping cameras system on a vehicle online These approaches are sensitive to the localization accuracy of the calibration tools and are failure when the cameras are unable to move. Ali et al [12] proposed an approach for simultaneously recovering the trajectory of a target and the external calibration parameters of non-overlapping cameras. This type of approaches cannot meet the accuracy demand of visual measurement. Camera parameter A1 and the relation [R' t'] between mirrored screen and the camera coordinate system can be obtained based on the pinhole model by moving mirror 1 to at least three arbitrary positions:
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