GetPelvisOrientation determines the turn angle, angular velocity and angular acceleration between the pelvis and the GCS using both the euler method and a simple vector approach ARGUMENTS data ... zoodata containing the pelvis channels PELO, PELA filt ... filter settings. Default no filter RETURNS data ... data with new channels added NOTES: - This is the same calculation as the PiG based on Cardan sequence YXY. See Kadaba et al. 1990 "Measurement of Lower Extremity Kinematics During Level Walking". Journal of Orthopaedic Research. Therefore the raw turn angle is the same as RPelvisAngles(:,3) from PiG. Except, here we can make sure turn angle is from 0 to 90 deg since. - PiG changes its reference axis based on direction of progresion (see PIGmanual ver1). Here I follow this convention and "switch" axes at the +/- 45 deg mark. This causes a small discontinuity that is ALWAYS filered Updated October 20th 2013 old (weak) computation is kept commented below Updated Dec 3rd 2013 - Turn angle computed by Euler and vector method consistently work