A light reference system includes a first, second and third rail followers. The second rail follower is disposed between the first and third rail followers. First and second light sources are disposed on the first and third rail followers and operable to emit light towards the second rail follower. First and Second imaging devices are disposed on the second rail follower. The first imaging device is operable to receive the light emitted by the first light source and provide first image data. The second imaging device is operable to receive the light emitted by the second light source and provide second image data. A processing device is configured to perform a measurement, based on the first and second image data, indicating a relative position of the second rail follower with respect to at least one of the first and third rail followers.