3-D ATTITUDE REPRESENTATION OF HUMAN JOINTS - A STANDARDIZATION PROPOSAL

In view of the singularities, asymmetries and other adverse properties of existing, three-dimensional definitions for joint and segment angl es, the present paper proposes a new convention for unambiguous and ea sily interpretable, 3-D joint angles, based on the concept of the atti tude 'vector' as derived from Euler's theorem. The suggested standard can be easily explained to non-mathematically trained clinicians, is r eadily implemented in software, and can be simply related to classical Cardanic/Eulerian angles. For 'planar' rotations about a coordinate s ystem's axes, the proposed convention coincides with the Cardanic conv ention. The attitude vector dispenses with the 'gimbal-lock' and non-o rthogonality disadvantages of Cardanic/Eulerian conventions; therefore , its components have better metrical properties, and they are less se nsitive to measurement errors and to coordinate system uncertainties t han Cardanic/Eulerian angles. A sensitivity analysis and a physical in terpretation of the proposed standard are given, and some experimental results that demonstrate its advantages.