水下三维物空间坐标的重构精度分析

Reconstruction Accuracy Analysis Underwater Three-dimensional Object-space Coordinate

目的:水下运动学数据的精度对于游泳项目的技术动作分析十分重要,利用防水摄像装置对标定框架上的有效点在水下和空气中进行三维重构,旨在验证不同测试环境和不同大小的标定空间对水下三维重构精度的影响,为水下游泳的器材研发提供一定的参考和依据。方法:2台水下摄像机同步拍摄放置在泳池里的标定框架(2 m×2 m×1 m),标定框架采取2种不同大小的标定空间,分别对同样数目的控制点(12个)和有效点(4个)分别在水下和空气中进行三维重构,重构精度通过4个有效点的均方根(RMS)重构误差来表示,利用DLT算法和ARIEL软件进行标定重构和数字化。结果发现,在整体标定空间控制点的RMS重构误差在X、Y、Z轴上为:(ⅰ)5.60 mm、10.44 mm和3.74 mm(水下),(ⅱ)4.89 mm、4.89 mm和3.96 mm(空气);局部标定空间为(ⅰ)5.29 mm、9.18 mm和3.02 mm(水下)(ⅱ)1.44 mm、1.11 mm和3.25 mm(空气)。结论:由于光线折射不论标定空间的大小,水下三维重构所得到的RMS重构误差都高于空气中的测量,Y轴最为明显;随着标定空间的增大,两种测试环境下的RMS重构误差均随之增大。

Accuracy of kinematical data is of decisive importance in motion analysis particularly,the aim of this study was to assess the reconstruction accuracy in different environment and calibration volumes with different size on validation points of calibration frames with waterproof camera housings,and provide some methods for equipment exploitation in swimming.Methods： The calibration frame（2×2×1m） was placed in a swimming pool and was recorded simultaneously by two underwater synchronized cameras.The calibration of the recording space was performed using two different-sized calibration frames,the reconstruction accuracy of three-dimensional object space coordinate was determined in static condition both underwater and in the air,4 validate markers and 12 control points were digitized in global calibrated space and local calibrated space with underwater cameras in water and air respectively.The reconstruction accuracy was determined by calculating the root mean square（RMS）error for reconstruction of four validation points on the calibration frames.Results： Direct linear transformation（DLT） methods were used to calculate reconstruction coordinate of the validate marker.The average root mean errors（RMS） in global calibrated space were： 1） 5.60mm,10.44mm and 3.74mm underwater and 2） 4.89mm,4.89mm and 3.96mm of air in x,y and z axis respectively;and in the local calibrated space were： 1） 5.29mm,9.18mm and 3.02mm underwater and 2）1.44mm,1.11mm and 3.25mm in air.Conclusion： The results revealed that the RMS error was greater during underwater analysis,due to refraction,and it was increased particularly in the Y axis as the dimensional of the calibration volume were increased.