The next step is to measure or acquire the offsets between the frames. It is reasonable to assume that the acquisition orders for telescope pointing are available as ancillary data. If they are not, there should be an automatic way of finding these offsets with a minimal chance of error. Last, users may want to use their own method to detect offsets and feed their input into the algorithm for ultimate refining. We discuss here a cross-correlation method used both for offset detection and refining.