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Relative quaternion to global with uncertainty

in this perfect tutorial i found how i can compose two poses with uncertainty and how i can transform one representation to another with uncertainty http://ingmec.ual.es/~jlblanco/papers/jlblanco2010geometry3D_techrep.pdf. Let's suppose I have one global point which represent 6 dof and 6 confidence and another one also representing by 6 dof and 6 confidence. How can I get "mean" point with uncertainty.