One embodiment relates to a method of sensing motion of an optical sensor relative to a surface. A first resolution and a second resolution are set. Measurement signals are obtained from a sensor array, and the motion of the optical sensor relative to the surface is tracked using the measurement signals. The tracking of the motion in a first dimension is performed at the first resolution, and the tracking of the motion in a second dimension is performed at the second resolution. Another embodiment relates to an optical sensor apparatus for sensing motion relative to a surface, wherein the tracking of the motion is performed at a variable resolution along each of two axes. Other embodiments and features are also disclosed.