Tweak Pipeline

This is an outline of the pipeline that will be used for the WCS tweak.

1. Use the original WCS in the image (ie, the WCS we believe to be roughly correct, possibly as produced by the BlindPipeline) to determine the approximate image footprint; grab all catalog stars (from USNO-B1.0 or SDSS or 2MASS) near that footprint.
2. Select from among the image sources found by the SourceDetectPipeline the brightest N, where N is somehow related to the number of catalog stars obtained near the image footprint in the first step.
3. Run Fink-Hogg algorithm (Hough transform) against catalog stars and update the CRVAL in the WCS to produce shifted WCS.
4. Run first-order tweak (ie, believing but not modifying the polynomial distortions in the original WCS), minimizing a chi-squared that includes terms for image sources that match catalog stars, with the shifted WCS as the starting point, to produce first-order tweaked WCS.
5. If requested, tweak up to higher order (ie, fit for and modify polynomial distortions) to produce tweaked WCS.
6. If requested, run the meta-tweak code to produce meta-tweaked WCS as follows:
   1. Find all images (in the astrometry.net archive) that plausibly overlap this one, and all those that plausibly overlap those, and so-on by friends-of-friends to produce an overlap group of images.
   2. Optimize WCS of all the images in the overlap group simultaneously, minimizing a chi-squared that includes terms for image sources that match catalog stars, and terms for image sources that match image sources from other, overlapping images.

Also see TweakExperiments