MoBL ARMS model: How to get Euler angles of local coordinate system transformation against global coordinate system

[Rejin Varghese]

Hi experts,

I am working with the MoBL ARMS model and I want to know the Euler Angles of the JCS fixed to the humerus, as the shoulder joint is moved in different DoFs. 2 of the 3 coordinates representing the 3 DoFs at the humerus - elv_angle and shoulder_elv don't represent the Euler angles at the humerus, as the coordinates are defined at different bones. Please find attached snapshots of the two coordinate systems being referred to.

snapshotOpenSim.PNG (36.84 KiB) Viewed 569 times

I wanted to try and get the Euler angles that define the transformation between the local (at humerus) and global coordinate system. Could someone please help me on how to get it within the MOT files etc. I am guessing I could use the API and extract it, but wanted to see if I could get them by making something active in the XML file, so that I can get that information in the MOT file itself. I am also attaching the opensim file and a static calibration trial for reference.

I hope someone could help me get through this problem.

Thank you very much in advance.

Regards,

Rejin

[Dimitar Stanev]

Maybe you can perform a BodyKinematics analysis using the AnalyzeTool. This should report the position and orientation of each body wrt the ground frame. In case that you need to specify the frame of interest, it is possible to attach a dummy body on the humerus oriented accordingly.

[Rejin Varghese]

Thank you very much for your reply Dimitar. I'll try to implement your suggestion.

Regards,

Rejin