The output angles for all joints are calculated from the YXZ Cardan angles derived by comparing the relative orientations of the segments proximal (parent) and distal (child) to the joint.
The knee angles are calculated from the femur and the Untorsioned tibia segments, while the ankle joint angles are calculated from the Torsioned tibia and the foot segment.
In the case of the feet, because they are defined in a different orientation to the tibia segments, an offset of 90 degrees is added to the flexion angle. This does not affect the Cardan angle calculation of the other angles because the flexion angle is the first in the rotation sequence.
The progression angles of the feet, pelvis, thorax and head are the YXZ Cardan calculated from the rotation transformation of the subject's progression frame for the trial onto each segment orientation.
The following topics provide further details.
- Angle definitions
- Plug-in Gait kinematic variables
- Upper body angles as output from Plug-in Gait
- Lower body angles as output from Plug-in Gait