Orientation angle of center of mass of vertebrae

[Nima Heidari]

Hello all!

Does OpenSim consider the orientation angle of the center of mass of vertebrae of the spine?
I checked out XML codes for different models (for example, https://simtk.org/projects/kuo-head-neck), and (based on what I checked out), the orientation with respect to parent is 0. (<orientation>0 0 0</orientation>). And I could not find out any other information in the XML files.
This orientation angle is important for dynamic analysis in Multibody Dynamic Simulation software.
I would be grateful if you help me out.

Bests,
Nima

[Carmichael Ong]

The "orientation" in these models usually refers to the orientation of the joint frame in either the parent or child frame, and is not related to the location of the center of mass. In OpenSim and Simbody (the mutlibody dynamics engine underneath OpenSim), the center of mass is a point, and thus there is no orientation that is associated with a point.

If there are specific questions about the model itself, it may be best to contact the authors of the paper directly for more information too.