Creating models via markers

[Jonathan Lin]

Hello,

I am a new OpenSim user. I have been looking for a easy to use, general way to create kinematic models (ie .osim files) from motion capture data. I recognize that creating kinematic models are not trivial, but our research lab studies both humans, as well as robots and props that we want to model as well. For humans, we can likely use an existing model, but this would not be possible with robots.

I wasn't able to find reference material on how creating a model, so I thought I post here. What I was hoping to do is:
- capture a set of motion capture data
- load the mocap data in OpenSim and define joint centres/axis with respect to marker positions
- link together joint centres to create a kinematic chain
- rotate body segments to a pre-defined pose (ie the <location_in_parent> line in the osim file, instead of being the thigh being [0.05 0.05 0.30 m] because the participant was standing a certain way, I want to be able to rotate the pose saved in the osim file to be [0 0 0.30 m])
- rescale this kinematic model to different participant sizes

My immediate goal is to use these models to generate inverse kinematics, but I am also interested in writing converters for the osim file structure to convert the kinematic model to other file formats so we can use it with our optimal control simulation software.

Is this model creation pipeline possible in OpenSim?

Thank you.

[John Davis]

Yes, this is very doable with the MATLAB or Python API. You might find the 'Building a Dynamic Walker in MATLAB' tutorial useful since it more or less does what you want, except without using marker data.