"Calibration method for panoramic 3D shape measurement with plane mirrors," Opt. Express (2019)

[120] W. Yin, S. Feng, T. Tao, L. Huang, S. Zhang, Q. Chen, C. Zuo, “Calibration method for panoramic 3D shape measurement with plane mirrors," Opt. Express, 27(25), 36538-36550 (2019)

Abstract

High-speed panoramic three dimensional (3D) shape measurement can be achieved by introducing plane mirrors into the traditional fringe projection profilometry (FPP) system because such a system simultaneously captures fringe patterns from three different perspectives ( i.e., by a real camera and two virtual cameras in the plane mirrors). However, calibrating such a system is nontrivial due to the complicated setup. This work introduces a flexible new technique to calibrate such a system. We first present the mathematical representation of the plane mirror, and then mathematically prove that it only requires the camera to observe a set of feature point pairs (including real points and virtual points) to generate a solution to the reflection matrix of a plane mirror. By calibrating the virtual and real camera in the same world coordinate system, 3D point cloud data obtained from real and virtual perspectives can be automatically aligned to generate a panoramic 3D model of the object. Finally, we developed a system to verify the performance of the proposed calibration technique for panoramic 3D shape measurement.

"Large depth-of-field 3D shape measurement using an electrically tunable lens," Opt. Express (2019)

X. Hu, G. Wang, Y. Zhang, H. Yang, and S. Zhang, “Large depth-of field 3d shape measurement using an electrically tunable lens," Opt. Express 27(21), 29697-29709 (2019).

Abstract

The state-of-the-art 3D shape measurement system has rather shallow working volume due to the limited depth-of-field (DOF) of conventional lens. In this paper, we propose to use the electrically tunable lens to substantially enlarge the DOF. Specifically, we capture always in-focus phase-shifted fringe patterns by precisely synchronizing the tunable lens attached to the camera with the image acquisition and the pattern projection; we develop a phase unwrapping framework that fully utilizes the geometric constraint from the camera focal length setting; and we pre-calibrate the system under different focal distance to reconstruct 3D shape from unwrapped phase map. To validate the proposed idea, we developed a prototype system that can perform high-quality measurement for the depth range of approximately 1,000 mm (400 mm – 1400 mm) with the measurement error of 0.05%. Furthermore, we demonstrated that such a technique can be used for real-time 3D shape measurement by experimentally measuring moving objects.

"Pixel-by-pixel absolute phase retrieval assisted by an additional three-dimensional scanner," Appl. Opt., (2019)

Y. An and S. Zhang, “Pixel-by-pixel absolute phase retrieval assisted by an additional three-dimensional scanner”, Appl. Opt., 58(8), 2033-2041, 2019, doi:10.1364/AO.58.002033

Abstract

This paper presents a novel absolute phase unwrapping method assisted by a low-cost three-dimensional (3D) scanner. The proposed absolute phase unwrapping method leverages a low-cost 3D scanner to capture rough 3D data of the scene, and transforms the rough 3D data to the world coordinate system to generate an artificial reference phase map Φ_. By referring to Φ_, we can do absolute phase unwrapping directly without projecting any additional patterns, such that the digital fringe projection (DFP) system can achieve higher measurement speed. We develop a multi-resolution system consisting of a DFP system and Kinect V2 to validate our method. Experiments demonstrate that our method works for a large depth range, and the speed of the low-cost 3D scanner is not necessarily the maximum speed of our proposed method. Assisted by Kinect V2 whose maximum speed is only 30Hz, our DFP system achieves 53Hz with a resolution 1600x1000 pixels when we measure dynamic objects that are moving in a large depth range of 400mm.