COMPARISON OF TWO METHODS FOR CALCULATING 3-DIMENSIONAL BALL SPIN, AND ITS APPLICATION TO SOCCER KICKING

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The aim of this study was to select an appropriate computational method for determining both spin axis direction, and spin rate during soccer ball flight. Calculation methods of Cross-Product (CP) and Singular Value Decomposition (SVD) were compared on a stationary spinning ball under laboratory conditions, using data collected from 10 Vicon MX cameras tracking 5mm hemispherical ball markers at 500Hz. When the ball was spun at 371 ± 15 RPM, spin axis orientation appeared close to ‘real’ values, yet CP showed greater error in RPM estimation. Comparison of the methods during a kick showed no significant difference for spin rate calculation, yet CP underestimated the x and y spin axes, and overestimated spin around the z axis. It was proposed that SVD is used in future to estimate ball spin parameters, especially during kicking where marker occlusion may be more prevalent.