Why quaternions are not used more in biomechanics?
something to do with interpretation. Euler angles can be associated with the rotations in a mechanical linkage or 3-D goniometer (Grood and Suntay, J Biomech Eng, 1983). The other representations work well for computation but are not so easily interpreted. On the other hand, Woltring makes some good points on error propagation in his 1994 paper (J Biomech 27:1399-1414). Near gimbal lock, Euler angles become increasingly sensitive to measuring errors. For the newcomers on Biomch-L, I also recommend reading the debate between Grood and Woltring, about 10 years ago on Biomch-L: http://isb.ri.ccf.org/biomch-l/files/angles3d.topic Ton van den Bogert Department of Biomedical Engineering Cleveland Clinic Foundation 9500 Euclid Avenue (ND-20) Cleveland, OH 44195, USA Phone/Fax: (216) 444-5566/9198 — I think Ton has explained it very well. Quaternions are not used because they are difficult to interpret. Even the engineers will have difficulty in visualising what is happening, let alone doctor
