A method of determining a desired relative position between a first object of a lithographic apparatus and a second object of the lithographic apparatus. Generating a measurement signal representing a position of the first object relative to the second object, at an initial relative position. Determining a gradient associated with the initial relative position, based on the measurement signal. Determining a position set point based on the gradient and wherein the position set point comprises a three-dimensional dither signal. Controlling the position of the first object relative to the second object to a further relative position, based on the position set point.