A method for determining relative angles and/or trigonometric functions of the relative angles between coupled rigid bodies arranged in a series, where the series includes at least a rigid body coupled to a previous rigid body. The method includes obtaining a gravitational acceleration vector and an angular velocity of the previous rigid body and a gravitational acceleration and an angular velocity of the rigid body. The relative angles and/or trigonometric functions of the relative angles are determined without using absolute angles of the rigid bodies.