Poor marker placement

Hello

I have got Plug-in-Gait data with some poor marker placements at the lateral thigh and lateral tibia. This has led to a shift in the orientation of the joint axes with both being rotated externally.

Is there a way to correct this in Anybody before calculation of joint force? Could I for example rotate the tibia so that its frontal plane aligns with that of the foot?

Is it possible to create a virtual marker on the tibia which is offset from the original tibia marker so that the tibia rotation can be corrected. I believe that the alignment of the foot is correct and would like to use it as a reference as to the rotation of the joint axis of the tibia.

I appreciate any input and am happy to clarify what I am trying to say if it is difficult to understand. Many thanks

Asif

Dear Asif,

The easiest way is to modify those marker locations in the ‘Markers.any’ file in the Input folder of the MoCapModel.

Best regards,
Moonki

Hi

I would only like to use a virtual marker in order to calibrate the joint axes. I would not like this marker however to be tracked during kinematic analysis. If I change the values in Markers.any this will change the initial guess for the marker positions on the model.

Is there a way to calibrate joint axes with a virtual marker but have the motion tracked by the original marker?

Hi Asif,

Fundamentally this is possible it will however require a bit of work to do this, since the model is not prepared for this setup specifically.

We have in the model a definition of a knee joint axis which is controlled by two points, but these points are not created to be editable.

If you open the LegTLEM/Seg.any file and search for “BONY_LANDMARK_DEFINED_JOINTAXIS”
you will find the definition of this joint using points.

I would suggest you do the following:
[ul]
[li]use AnyMechObjectExclude to exclude the knee joint (see small example in AnyBodyStudy object in the reference manual)
[/li][li]create your own knee joint definition similar to the one mentioned above
[/li][li]include the new knee joint from your study
[/li][/ul]

So it is possible to do this, and can be done without altering the body model, but it requires a bit of work.

Best regards
Søren