Frame for contact forces

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Hi,

The documentation for a gazebo::physics::contact says:

"All forces and torques are in the world frame. All forces and torques are relative to the center of mass of the respective links that the collision elments are attached to."

Does this mean that the forces and torques are at the world frame origin or at a frame that's got its position origin at the CoM of the link but has the rotation of the world? Is it truly the CoM of the link and not the link origin?

Thanks!