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Dear guys.

Thanks for your reading.
I want to know how the CoM calculation of BodyKinematics works in the Analyze Tool of OpenSim 3.3? For example, what is the mathematic equation the OpenSim used?

LI Dongdong

You can find the code in BodyKinematics.cpp; the accelerations are computed starting from here: https://github.com/opensim-org/opensim- ... s.cpp#L541. The API documentation may be helpful to look up the methods that are called (e.g., getAccelerationInGround: https://simtk.org/api_docs/opensim/api_ ... 285ccd015e).

Dear Prof. Uchida,

Thanks for your reply. I found how the position and acceleration are calculated. However, I found the function "get_mass_center()". It seems to get the mass center of the body. So I want to know how the function "get_mass_center()" works? What's the equation it uses?

Thanks

I found the function "get_mass_center()". It seems to get the mass center of the body. So I want to know how the function "get_mass_center()" works? What's the equation it uses?

There is no equation because the center of mass is a property of the Body (see the API documentation for the get_mass_center() method: https://simtk.org/api_docs/opensim/api_ ... fdc91b48e3). Properties are described in the User's Guide in the Confluence documentation (see the "Property Editor and Outputs List" page under "What is a model property?": https://simtk-confluence.stanford.edu/d ... lproperty?) and in the API documentation (see the "API Guide" page under "Property": https://simtk.org/api_docs/opensim/api_ ... l#property).