Computation of rigid body motion parameters from video-based measurements

The objective of the work is to compare and improve the accuracy of existing methods for the computation of rigid body parameters from positions, velocities and accelerations of a set of non colinear anatomical landmarks. Instead of the common Euler angles, Cardan angles or Bryant angles, the results are expressed in terms of the screw axis parameters (i.e. axis versor and rotation angle). In clinical analysis the physical meaning of this axis is surely better understood than the named angles. The paper summarizes also the main steps of noteworthy algorithms for the extraction of finite and infinitesimal screw motion parameters from noisy measurements of markers positions, velocities and accelerations. The sensitivity to data errors of the methods reviewed has been investigated by means of numerical tests. A commercial human motion analysis was also used for the field testing.