US Patent 9618332 Method and apparatus for position determination

Embodiments of the invention provide a method of determining a position of an object with respect to incident radiation, comprising iteratively determining at least one of an object function indicating one or more characteristics of an object and a probe function indicative of one or more characteristics of incident radiation, iteratively determining the position of the object, wherein the iteratively determining the position of the object comprises cross correlating first and second estimates of the object function or the probe function, determining a location of a peak of the cross correlation, and determining a translation deviation indicative of a difference in position of the object between the first and second estimates based on the location of the peak.