Abstract: A method for providing a yaw angle (105a) between a first vehicle (110) coupled to a second vehicle (100), comprises: receiving an image of the first vehicle from a camera (101) mounted on the second vehicle; performing (210) a polar transformation on the image to form a polar image (400) in a polar space having an origin corresponding to a location of a pivot point (303) of the coupling (302) to the second vehicle in the received image coordinate space; estimating (230) an optical coupling angle by analysing the content of the polar image; receiving a signal from an odometer (102) mounted on the first or second vehicle; estimating a kinematic coupling angle from the signal and a kinematic model of the first vehicle and the coupled second vehicle; and combining the estimated optical coupling angle and the estimated kinematic coupling angle to provide the coupling angle.