A CALIBRATION FRAME FOR 3D SWIMMING ANALYSIS

Abstract

The purpose of this study was to construct a calibration frame for accurate threedimensional analysis of swimming and to assess its accuracy and reliability. A 6.75 m3 frame was constructed. The frame was positioned in a 25 m pool so that half was above and half below the water surface and recorded with four underwater and two above water synchronised cameras. Direct linear transformation methods were used to estimate marker locations on the frame. Comparison among different numbers of control points showed the set of 20 points to produce the most accurate results. Selection of the most accurate control points improved the accuracy of the measurements even when only 10 control points were used. The frame was found to have high accuracy (mean errors: 3.3 mm, 2.6 mm and 4.0 mm; root mean square errors: 3.9 mm, 3.8 mm and 4.8 mm) and reliability (standard deviation: 0.4 mm, 0.5 mm and 0.4 mm).