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Which inverse kinematics method does OpenSim use?

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  • Which inverse kinematics method does OpenSim use?

    Disclaimer: This is a duplicate of this, as I figured it was more appropriate to post directly on the OpenSim website. Feel free to ask me to delete it if you think I should.

    Dear all,

    I am currently reading this article, and I am quite puzzled with the amount of solutions there are to the kinematic problem. I am wondering which one of these OpenSim uses.

    - It is definitely a numerical approach, rather than analytical
    - There is no learning, so it is not a data-driven approach
    - I don't think there is any heuristics involved
    - Gauss-Newton optimization converges faster, only if they do. OpenSim is robust enough that I would think it uses a Jacobian approach instead.

    However, nowhere in the OpenSim papers nor in the documentation, can I see any mention of the Jacobian. I think I gathered that it is a non-linear least-square problem, solved with global optimization with the Levenberg-Marquard algorithm. How does that imply that this uses a Jacobian method?

    Subsidiary question: are forward and direct kinematics really synonym? The 6DoF way of solving joint angles (which is analytical, rather than numerical) seems to be sometimes called direct kinematics.
    If so, then I suppose it is wrong to say that inverse kinematics solve joint angles from point coordinates, while forward/direct kinematics solves point coordinates from joint angles?

    Last edited by David Pagnon; November 20, 2022, 03:25 PM.