While structural displacements are essential information for structural health monitoring, they are not being widely used in practice due to the inconvenience. Recently, vision-based displacement measurement methods have been introduced, which are more convenient and cost effective. However, vision-based methods have generally not been used primarily for the continuous monitoring of structures, due to spatial constraints on obtaining an appropriate location to secure the field of view. A vision device shows not only the changes of objects in the scene but also the relative changes of view according to changes in the position to which it is mounted. Accordingly, this study proposes a methodology for measuring the structural displacement of a location where a camera is mounted, based on a camera motion-induced relative view change. The method is organized into three steps. First, camera calibration is conducted with background targets to derive the camera parameters and coordinates of the target feature points. Second, by tracking the relative changes in the feature points according to the camera motion, the changed 2D-image coordinates of the points are derived. Third, the displacement is calculated through the relationship between the changed 2D-image coordinates and fixed 3D-world coordinates of the target feature points using the camera parameters. The changes in view according to the camera motion are analyzed with simulation tests, and the applicability of the proposed method is verified through experimental tests. The results show that the proposed method can be used to rationally measure structural displacements.

中文翻译：

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使用安装在结构上的相机进行基于视觉的位移测量，结构外部具有固定的背景目标

虽然结构位移是结构健康监测的重要信息，但由于不便，它们在实践中并未广泛使用。最近，已经引入了基于视觉的位移测量方法，这种方法更加方便且具有成本效益。然而，基于视觉的方法通常不主要用于结构的连续监测，因为空间限制在获得适当位置以确保视野方面存在空间限制。视觉设备不仅可以显示场景中物体的变化，还可以根据其安装位置的变化显示视图的相对变化。因此，本研究提出了一种基于相机运动引起的相对视图变化来测量安装相机位置的结构位移的方法。该方法分为三个步骤。首先，对背景目标进行相机标定，得到相机参数和目标特征点的坐标。其次，通过根据相机运动跟踪特征点的相对变化，导出点的变化后的二维图像坐标。第三，使用相机参数通过改变的 2D 图像坐标与目标特征点的固定 3D 世界坐标之间的关系计算位移。通过仿真测试分析了摄像机运动引起的视野变化，并通过实验测试验证了所提方法的适用性。结果表明，该方法可用于合理测量结构位移。对背景目标进行相机标定，得到相机参数和目标特征点的坐标。其次，通过根据相机运动跟踪特征点的相对变化，导出点的变化后的二维图像坐标。第三，使用相机参数通过改变的 2D 图像坐标与目标特征点的固定 3D 世界坐标之间的关系计算位移。通过仿真测试分析了摄像机运动引起的视野变化，并通过实验测试验证了所提方法的适用性。结果表明，该方法可用于合理测量结构位移。对背景目标进行相机标定，得到相机参数和目标特征点的坐标。其次，通过根据相机运动跟踪特征点的相对变化，导出点的变化后的二维图像坐标。第三，使用相机参数通过改变的 2D 图像坐标与目标特征点的固定 3D 世界坐标之间的关系计算位移。通过仿真测试分析了摄像机运动引起的视野变化，并通过实验测试验证了所提方法的适用性。结果表明，该方法可用于合理测量结构位移。