Barron and I spent the afternoon discussing his project to measure the dates at which images were taken. To do the best job, he must measure the best centroids; up to now he has been using Robert Lupton's (Princeton) algorithm implemented in the SDSS image processing code. This algorithm fits a set of one-dimensional parabolae; it is a fast numerical approximation to fitting the peak of each source with a two-dimensional parabolic surface. Jon's new centroiding code actually does the full-up parabolic surface fit to the peak of each source, and it appears to return centers that are better than the Lupton code, although at the (significant) expense of compute time.
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