Laboratory for Biomechanics and Biomaterials, Department of Orthopaedic Surgery, Hannover Medical School, Germany.
Biomed Eng Online. 2011 Feb 1;10:12. doi: 10.1186/1475-925X-10-12.
Orthopaedic research projects focusing on small displacements in a small measurement volume require a radiation free, three dimensional motion analysis system. A stereophotogrammetrical motion analysis system can track wireless, small, light-weight markers attached to the objects. Thereby the disturbance of the measured objects through the marker tracking can be kept at minimum. The purpose of this study was to develop and evaluate a non-position fixed compact motion analysis system configured for a small measurement volume and able to zoom while tracking small round flat markers in respect to a fiducial marker which was used for the camera pose estimation.
The system consisted of two web cameras and the fiducial marker placed in front of them. The markers to track were black circles on a white background. The algorithm to detect a centre of the projected circle on the image plane was described and applied. In order to evaluate the accuracy (mean measurement error) and precision (standard deviation of the measurement error) of the optical measurement system, two experiments were performed: 1) inter-marker distance measurement and 2) marker displacement measurement.
The first experiment of the 10 mm distances measurement showed a total accuracy of 0.0086 mm and precision of ± 0.1002 mm. In the second experiment, translations from 0.5 mm to 5 mm were measured with total accuracy of 0.0038 mm and precision of ± 0.0461 mm. The rotations of 2.25° amount were measured with the entire accuracy of 0.058° and the precision was of ± 0.172°.
The description of the non-proprietary measurement device with very good levels of accuracy and precision may provide opportunities for new, cost effective applications of stereophotogrammetrical analysis in musculoskeletal research projects, focusing on kinematics of small displacements in a small measurement volume.
专注于小测量体积中小位移的骨科研究项目需要一种无辐射的三维运动分析系统。立体摄影测量运动分析系统可以跟踪无线、小、轻量级标记附着在物体上。从而可以将通过标记跟踪对测量物体的干扰保持在最低限度。本研究的目的是开发和评估一种非位置固定的紧凑型运动分析系统，该系统针对小测量体积进行配置，并能够在跟踪小圆形平板标记时进行缩放，同时跟踪小圆形平板标记相对于用于相机位姿估计的基准标记。
该系统由两个网络摄像头和放置在它们前面的基准标记组成。要跟踪的标记是白色背景上的黑色圆圈。描述并应用了检测图像平面上投影圆中心的算法。为了评估光学测量系统的准确性（平均测量误差）和精度（测量误差的标准偏差），进行了两项实验：1）标记间距离测量和 2）标记位移测量。
在 10 毫米距离测量的第一项实验中，总精度为 0.0086 毫米，精度为±0.1002 毫米。在第二项实验中，测量了从 0.5 毫米到 5 毫米的平移，总精度为 0.0038 毫米，精度为±0.0461 毫米。测量了 2.25°的总旋转量，总精度为 0.058°，精度为±0.172°。
对具有非常高精度和精度水平的非专有测量设备的描述可能为立体摄影测量分析在专注于小测量体积中小位移运动学的肌肉骨骼研究项目中的新的、具有成本效益的应用提供机会。
