
It is common in motion analysis to define one or more angles (userangles) based on the marker coordinates. Included in the userangle category are the projected joint angles, body lean angle, velocity vector angle, etc. Proper combination of the local reference frames and the points & vectors computed will provide flexibility and allow the user to define a variety of userangles to fulfill the analysisspecific needs. The major issues related to the userangle computation are
Userangles can be defined from points and/or lines (vectors). The legitimate entries for the points are the markers, joints and the segmental CMs while those for the lines are unit coordinate vectors of the global and local reference frames, segment vectors (the vector drawn from the proximal end to the distal end in a segment), and any kinematic and kinetic vectors computed through data processing. Kwon3D provides 5 different ways to define a userangle:
See the Software part for the details of the userangle definition methods. 
© YoungHoo Kwon, 1998 