Opensim output error

[saylee patkar]

Hi all,
I have executed opensim analysis with methodology as SCALE-IK-CMC. After CMC I am getting output for both knee joints as equal values whereas it should be different (noticed from vicon output).
What can be the reason for getting this error?

[Thomas Uchida]

You could be tracking the same markers on each leg, using a planar model, plotting one variable twice, etc. Are the knee joint angles identical in the IK results as well?

[saylee patkar]

Yes sir,
IK gives same knee flexion angles for both knee joints.
How to check if the same markers are tracked on each leg?

[Thomas Uchida]

Please see "Tutorial 3 - Scaling, Inverse Kinematics, and Inverse Dynamics" in the documentation: https://simtk-confluence.stanford.edu/d ... e+Dynamics.

[saylee patkar]

Thank you for your input sir.
I checked the IK with experimental data and also the message window. The maximum marker error occurred during the phase where, knee angle is not matching with the experimental data, for LASI.
This can be the issue for not getting desired output.
But I don't know how to solve this error.

[Thomas Uchida]

Please start by reviewing the recommendations on the "Getting Started with Inverse Kinematics" page in the documentation (under the "Best Practices and Troubleshooting" heading): https://simtk-confluence.stanford.edu/d ... leshooting. Other potential issues include poor model scaling or poor marker registration.

[saylee patkar]

Hello,
I tried scaling with different iterations and now my scaled model matches with the exprerimental data without much errors (I can see my model markers and experimental markers overlapping).
But even after this, there is 15-20 degrees of error in left knee flexion angle whereas the right knee flexion angle is same, when compared with the corresponding vicon output.
How knee angle is measured in opensim? Using markers locations or angle between bodies? Do I have to consider any offset in knee flexion while comparing with the vicon outputs?
Updating with the note: the subject is a healthy person. So there is soft tissue assumption consideration in vicon for calculating knee flexion angle. So is there any setting in the opensim where we can add the effect of bulky area will be considered while tracking markers?