Only the basic scheme was verified through static laboratory tests, so the efficiency and feasibility for dynamic measurements are still under scrutiny. More recently, Jeon et al. [3] introduced in 2011 a paired structured light for displacement measurement of structures. This system could simultaneously obtain the displacement and rotation of the measurement point. However, the system inhibitor had a complicated setup and required a transformation matrix to obtain the final results.Some current commercial contact-type tilt-meter sensors can provide a resolution up to 0.002 degree, as shown in Table 1. Basically, a commercial rotation angle measurement system usually consists of a tilt sensor, data cable, data logger, and data processing software, so the total cost of the system is still expensive.
The total cost of a commercial rotation angle measurement system usually varies from several hundred to several thousand US dollars, depending on a specific application.Table 1.Commercial tilt sensors.Painter and Shkel [1] have briefly reviewed some typical contact-type direct angle measurement technologies and pointed out their disadvantages. Inclinometers and magnetometers are highly sensitive to linear acceleration and environmentally induced magnetic fields, respectively. In addition, inclinometers only measure rotations about axes perpendicular to gravity, while magnetometers can only capture angular changes about axes parallel to gravity. Gyroscopes can produce large errors in as short as an hour, due to integration bias and noise.
The objective of this study is to develop a single-point rotational angle measurement system for large-scale civil structures using a multi-point vision-based system with high resolutions. Compared to commercial rotation angle measurement systems, the proposed system can measure static and dynamic rotational angles with high resolutions. Moreover, the system can be easily expanded to multi-point rotation angle measurement using the partitioning approach [2]. To verify the performance of this system, several laboratory and field tests were carried out on a three-story steel frame model, and on a five-story modal testing tower with a hybrid mass damper (HMD).2.?A Vision-Based Rotation Angle Measurement SystemThe configuration of the proposed system AV-951 is provided in Figure 1.
The initial assumption is that two camcorders, Cam01 and Cam02, are placed at the fixed location base of the structure or beyond the structure where there is no displacement and rotation (��0 = 0, and ��0 = 0). Cam01 and Cam02 will track targets T1 and T2, respectively. Another camcorder (Cam12) will aim at target T2. Displacements ��1 and ��2 are directly measured by Cam01 and Cam02, and reference 4 the displacement ��12 is the relative displacement of target T2 with respect to the tangential line of Cam12.