Abstract This study presents a new technique that enables entire surface geometric quality inspection (GQI) of planar-type prefabricated construction elements without registration of point cloud data. Laser scanning technology has gained much attention in the area of GQI of manufactured planar-type construction elements such as precast concrete (PC) elements during the fabrication or manufacturing stage, due to its speed and accuracy. However, the scope of existing GQI techniques using laser scanning are limited to single surface GQI of planar-type construction elements. Because of this, a registration process is inevitably necessary to merge different sets of point cloud data acquired at multiple scanning locations. The current multiple scans and registration approach for the GQI of planar-type construction elements are, however, time consuming and error prone due to registration errors. This study aims to develop a registration-free GQI technique that is capable of scanning invisible side surfaces of planar-type elements from the terrestrial laser scanner (TLS) using flat mirrors in order to tackle the limitations of the prior GQI studies. Firstly, the geometrical relationship between the flat mirror and the invisible surfaces of the planar-type element is identified based on the mirror reflection principle of laser beams. The virtual scan points of the invisible side surfaces generated by the flat mirror are then transformed to the location of the actual side surface based on the identified geometrical relationship and the mirror plane estimated using rectangular patches attached to the mirror. To investigate the feasibility of the proposed registration-free GQI technique, a series of tests on a laboratory-scale specimen with varying scan parameters are conducted. In addition, comparison tests with traditional registration methods are performed to further analyze the performance of the proposed technique in terms of GQI accuracy and efficiency. The results show that the proposed technique provides more accurate GQI results while reducing scanning time compared to traditional registration methods, demonstrating great potential for application in the GQI of planar-type prefabricated construction elements during the fabrication stage.

中文翻译：

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使用地面激光扫描的平面型预制构件的镜面辅助免注册几何质量检测

摘要 本研究提出了一种无需注册点云数据即可对平面型预制构件进行全表面几何质量检测 (GQI) 的新技术。由于其速度和精度，激光扫描技术在制造或制造阶段制造的平面型建筑元件（例如预制混凝土 (PC) 元件）的 GQI 领域备受关注。然而，使用激光扫描的现有 GQI 技术的范围仅限于平面型建筑元件的单表面 GQI。因此，不可避免地需要进行配准过程以合并在多个扫描位置获取的不同组点云数据。然而，当前平面型建筑元素 GQI 的多次扫描和配准方法是，由于注册错误而耗时且容易出错。本研究旨在开发一种免注册 GQI 技术，该技术能够使用平面镜从地面激光扫描仪 (TLS) 扫描平面型元件的不可见侧表面，以解决先前 GQI 研究的局限性。首先，根据激光束的镜面反射原理，确定平面镜与平面型元件的不可见面之间的几何关系。然后，根据识别的几何关系和使用贴在镜子上的矩形块估计的镜面，将由平面镜生成的不可见侧表面的虚拟扫描点转换为实际侧表面的位置。为了研究所提出的免注册 GQI 技术的可行性，对具有不同扫描参数的实验室规模样本进行了一系列测试。此外，还进行了与传统配准方法的对比测试，以进一步分析所提出技术在 GQI 准确性和效率方面的性能。结果表明，与传统配准方法相比，所提出的技术提供了更准确的 GQI 结果，同时减少了扫描时间，在制造阶段展示了在平面型预制构件的 GQI 中的巨大应用潜力。执行与传统配准方法的比较测试，以进一步分析所提出技术在 GQI 准确性和效率方面的性能。结果表明，与传统配准方法相比，所提出的技术提供了更准确的 GQI 结果，同时减少了扫描时间，在制造阶段展示了在平面型预制构件的 GQI 中的巨大应用潜力。执行与传统配准方法的比较测试，以进一步分析所提出技术在 GQI 准确性和效率方面的性能。结果表明，与传统配准方法相比，所提出的技术提供了更准确的 GQI 结果，同时减少了扫描时间，在制造阶段展示了在平面型预制构件的 GQI 中的巨大应用潜力。