The simulation of aerial movement--I. The determination of orientation angles from film data

Quantitative mechanical analyses of human movement require the time histories of the angles which specify body configuration and orientation. When these angles are obtained from a filmed performance they may be used to evaluate the accuracy of a simulation model. This paper presents a method of determining orientation angles and their rates of change from film data. The stages used comprise the synchronization of data obtained from two camera views, the determination of three-dimensional coordinates of joint centres, the calculation of an angle from a sequence of sine and cosine values and the curve fitting of angles using quintic splines. For each stage, other possible approaches are discussed. Original procedures are presented for obtaining individual error estimates of both the film data and the calculated angles to permit the automatic fitting of quintic splines for interpolation and differentiation and for deriving the time history of an angle as a continuous function from a sequence of sine and cosine values. The method is applied to a forward somersault with 1 1/2 twists and the average error estimate of 17 orientation angles is obtained as 2.1 degrees.