Closed formulae to determine the angular velocity of a body-segment based on 3D measurements

This paper suggests a simple method to determine the global coordinates of the angular velocity and the angular acceleration of a body segment determined by the coordinates of minimum three markers. There are commonly used calculations for the angular quantities basing on the "hypothesis" of planar motion. The usage of approximate methods can result in quantitative and qualitative errors that may completely disort the reality. The method mentioned here is theoretically absolutely correct and can be well used for smoothing noisy data.