Systematic accuracy and precision analysis of video motion capturing systems--exemplified on the Vicon-460 system

With rising demand on highly accurate acquisition of small motion the use of video-based motion capturing becomes more and more popular. However, the performance of these systems strongly depends on a variety of influencing factors. A method was developed in order to systematically assess accuracy and precision of motion capturing systems with regard to influential system parameters. A calibration and measurement robot was designed to perform a repeatable dynamic calibration and to determine the resultant system accuracy and precision in a control volume investigating small motion magnitudes (180x180x150mm(3)). The procedure was exemplified on the Vicon-460 system. Following parameters were analyzed: Camera setup, calibration volume, marker size and lens filter application. Equipped with four cameras the Vicon-460 system provided an overall accuracy of 63+/-5mum and overall precision (noise level) of 15mum for the most favorable parameter setting. Arbitrary changes in camera arrangement revealed variations in mean accuracy between 76 and 129mum. The noise level normal to the cameras' projection plane was found higher compared to the other coordinate directions. Measurements including regions unaffected by the dynamic calibration reflected considerably lower accuracy (221+/-79mum). Lager marker diameters led to higher accuracy and precision. Accuracy dropped significantly when using an optical lens filter. This study revealed significant influence of the system environment on the performance of video-based motion capturing systems. With careful configuration, optical motion capturing provides a powerful measuring opportunity for the majority of biomechanical applications.