Aiming at the problem of the low accuracy of projector calibration in a structured light system, an improved projector calibration method is proposed in this paper. One of the key ideas is to estimate the sub-pixel coordinates in the projector image plane using local random sample consensus (RANSAC). A bundle adjustment (BA) algorithm is adopted to optimize the calibration parameters to further improve the accuracy and robustness of the projector calibration. After system calibration and epipolar rectification, the mapping relationship between the pixel coordinates and the absolute phase in the projector image plane is established by using cubic polynomial fitting, and the disparity is rapidly solved by using the mapping relationship, which not only ensures the measurement accuracy, but also improves the measurement efficiency. The experimental results demonstrated that the average re-projection error after optimization is reduced to 0.03 pixels, and the proposed method is suitable for high-speed 3D reconstruction without the time-consuming homogenous point searching.

The phase 3-D coordinate mapping (P3DM) is an efficient 3-D reconstruction method for the in situ measurement. However, the conventional P3DM calibration method requires complex operation or an extra high-precision positioner stage, which is not suitable for the in situ calibration. A novel in situ calibration method for P3DM is proposed based on virtual planes. A series of virtual planes are generated, and the relationship between the artificial 3-D coordinates and the phases on each virtual plane by pixel is established. The proposed method only needs to capture the calibration board patterns at top and bottom positions to overcome the space limitation and reduce personal measurement error, so to achieve a high accuracy, simple, and low-cost in situ calibration. A small field-of-view (FoV) measurement system is developed with the usage of the proposed calibration method. The experimental results show that the measurement error with a standard deviation of $1.9 ~\mu \text{m}$ is obtained. The feasibility of the proposed method is verified by a successful application to a relay component assembly line.