simtk.org

Hello,

I was wondering if there is any post that explains what the "phantom bodies" are. They are bodies without center of mass and inertia. I use MoBL-ARMS dynamic upper limb model - OpenSim 3.2+. In the model, they are called scapphand, humphant, humphant1, and clavphant. What are their function? Do they affect inverse kinematics and dynamics results?

Thank you for your attention.

Jason(Woojae) Kim

In 3.3, joints can only be added with a body. If you look in the model file, you will see that each joint is nested inside a corresponding body. However, for complicated motions, you may want a complicated motion that involves multiple joints without having to add extra bodies (mass and inertia). In this case, you would create a 'phantom' body, one without mass or inertia, so that you can include the additional joint. This is not a great strategy for numerous reasons, but it is the choice of the person building the model.