By mj_contactForce(const mjModel* m,const mjData* d,int id, mjtNum* result) , I can get a 6D force/torque for one contact, in contact frame. But, how can I convert this force from contact frame to world frame, so that I can compare multiple contacts in the same reference? And I am also interested in how much force is exactly applied onto the object, so I also want to know how to convert the force from contact frame to the object frame. Thanks in advance!