3: Fine Astrometry Pipeline
The Fine Astrometry pipeline is run for each multi-observation stack chosen by the observation selection process to register the observations for a stack on a common astrometric frame.
The goal of this pipeline is to align the positions of all observations in the stack with the positions using a common tangent plane for all of them, designed to be as close as possible to the tangent plane of the observation with the largest number of bright sources. The derived astrometric corrections are typically small.
Use bright source results to align observations
For each stack, the observation with the most sources in its bright source list is designated the primary observation.
For each other observation in a stack, the bright source lists created in the Pre-Detect step are compared with that of the primary observation using the wcs_match tool, generating translation offsets for each observation. The final transformation is calculated as an exposure weighted average over all the observations. This transformation is applied to the aspect solution (asol) files, and stored in their XFM extension.
Output data products
The fine astrometry pipeline produces no data products, but modifies the asol3.fits files.