@article{lee_nie_han_2024, title={Automatic and Real-Time Joint Tracking and Three-Dimensional Scanning for a Construction Welding Robot}, volume={150}, ISSN={["1943-7862"]}, url={https://doi.org/10.1061/JCEMD4.COENG-14135}, DOI={10.1061/JCEMD4.COENG-14135}, abstractNote={Although welding is one of the essential steel fabrication processes, the American Welding Society expects that the labor shortage in the United States will reach a deficit of 360,000 welders by 2027. Developing an automatic robotic welding system could potentially alleviate the labor shortage and provide better welding quality. As a first step, this paper designs a system pipeline that can automatically detect different welding joints and plan and track the joints' trajectory with the initial point alignment in real time. There are rare studies that could achieve automatic initial point alignment in real time because the laser stripe's deformation is not obvious at the narrow weld. In this study, the target joint's endpoints were detected once the joint was detected on live video. Then, the joint trajectory was planned, and the robotic arm automatically aligned with the initial point and tracked the planned trajectory while scanning. The results demonstrate the accuracy and effectiveness of the proposed method.}, number={3}, journal={JOURNAL OF CONSTRUCTION ENGINEERING AND MANAGEMENT}, author={Lee, Doyun and Nie, Guang-Yu and Han, Kevin}, year={2024}, month={Mar} }
 @article{nie_bodda_sandhu_han_gupta_2022, title={Computer-Vision-Based Vibration Tracking Using a Digital Camera: A Sparse-Optical-Flow-Based Target Tracking Method}, volume={22}, ISSN={["1424-8220"]}, url={https://doi.org/10.3390/s22186869}, DOI={10.3390/s22186869}, abstractNote={Computer-vision-based target tracking is a technology applied to a wide range of research areas, including structural vibration monitoring. However, current target tracking methods suffer from noise in digital image processing. In this paper, a new target tracking method based on the sparse optical flow technique is introduced for improving the accuracy in tracking the target, especially when the target has a large displacement. The proposed method utilizes the Oriented FAST and Rotated BRIEF (ORB) technique which is based on FAST (Features from Accelerated Segment Test), a feature detector, and BRIEF (Binary Robust Independent Elementary Features), a binary descriptor. ORB maintains a variety of keypoints and combines the multi-level strategy with an optical flow algorithm to search the keypoints with a large motion vector for tracking. Then, an outlier removal method based on Hamming distance and interquartile range (IQR) score is introduced to minimize the error. The proposed target tracking method is verified through a lab experiment—a three-story shear building structure subjected to various harmonic excitations. It is compared with existing sparse-optical-flow-based target tracking methods and target tracking methods based on three other types of techniques, i.e., feature matching, dense optical flow, and template matching. The results show that the performance of target tracking is greatly improved through the use of a multi-level strategy and the proposed outlier removal method. The proposed sparse-optical-flow-based target tracking method achieves the best accuracy compared to other existing target tracking methods.}, number={18}, journal={SENSORS}, author={Nie, Guang-Yu and Bodda, Saran Srikanth and Sandhu, Harleen Kaur and Han, Kevin and Gupta, Abhinav}, year={2022}, month={Sep} }
 @article{lee_nie_han_2023, title={Vision-based inspection of prefabricated components using camera poses: Addressing inherent limitations of image-based 3D reconstruction}, volume={64}, ISSN={["2352-7102"]}, url={https://doi.org/10.1016/j.jobe.2022.105710}, DOI={10.1016/j.jobe.2022.105710}, abstractNote={Modular construction can lead to additional cost overruns and delays when a defect is found on the construction site and is not easily repairable. Researchers have developed various methods that use image-based 3D reconstruction for quality assessment, but they have inherent limitations, such as inconsistency and dealing with surfaces with reflectivity and limited visual features. Therefore, this paper presents a vision-based quality assessment method using cameras for prefabricated components by addressing these limitations. Specifically, this paper proposes a novel quality inspection method with sub-millimeter accuracy using cameras focused on leveraging camera poses (as opposed to 3D point clouds that are often not consistent in quality) from the image-based 3D reconstruction. The 3D point estimation by computing triangulation was used for achieving accurate measurement. The proposed method is validated using six different variances and two case studies – an aluminum pipe with a reflective surface and a fabricated concrete column. The results demonstrate the accuracy and effectiveness of the proposed method.}, journal={JOURNAL OF BUILDING ENGINEERING}, author={Lee, Doyun and Nie, Guang-Yu and Han, Kevin}, year={2023}, month={Apr} }