Method and apparatus for position determination

An apparatus for determining a position of an object with respect to incident radiation, comprising:

• a detector for measuring an intensity of a wavefield incident thereon scattered from an object;
• and
• a processing device arranged:
• to receive intensity data from the detector,
• to iteratively determine at least one of an object function indicating one or more characteristics of the object and a probe function indicative of one or more characteristics of incident radiation, and
• to iteratively determine the position of the object with respect to the incident radiation by:
• cross correlating first and second estimates of the object function or the probe function indicating of one or more characteristics of the incident radiation,
• 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.

A non-transitory computer-readable medium containing computer executable instructions which, when executed by a computer, perform operations 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;
• and
• 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 die first and second estimates based on the location of the peak.