Enforce Foot Flat through Marker Adjustment in Scaling

[Evan Dooley]

Hello again,

I am trying to make sure that when I scale my base model to the size of each subject and update the marker positions on the subject specific models, the feet stay flat on the floor. I am sure the feet are flat on the floor in the static position (being used for scaling) as we have video recording of this.

Does anyone have a good method for enforcing the feet stay flat relative to the floor while using the scale tool?

I first tried creating a 6 DoF joint between each foot and the floor, but this closes the loop back to ground and the model does not initialize as it does not conform to the object tree structure. I have also tried applying various constraints (and combinations), including creating a dummy body with the coordinate I would like to enforce coupling too with no luck. There does not seem to be a "Custom Constraint" option, so I could just remove the foot's ability to flex and invert.

Any suggestions or ideas would be greatly appreciated. I feel like I may be missing something.

As always, thanks for your help,
Evan

[Thomas Uchida]

There are a few strategies (e.g., project markers onto the floor). I think this is discussed in the "OpenSim Webinar: Tips and Tricks for Data Collection, Scaling and Inverse Kinematics in OpenSim" video on the OpenSimVideos YouTube channel: https://youtu.be/ZG7wzvQC6eU.