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gbdes derives photometric and astrometric calibration solutions for complex multi-detector astronomical imagers. The package includes routines to filter catalogs down to useful stellar objects, collect metadata from the catalogs and create a config file holding FITS binary tables describing exposures, instruments, fields, and other available information in the data, and uses a friends-of-friends matching algorithm to link together all detections of common objects found in distinct exposures. gbdes also calculates airmasses and parallactic angles for each exposure, calculates and saves the expected differential chromatic refraction (DCR) needed for precision astrometry, optimizes the parameters of a photometric model to maximize agreement between magnitudes measured in different exposures of the same source, and optimizing the parameters of an astrometric model to maximize agreement among the exposures and any reference catalogs, and performs other tasks. The solutions derived and used by gbdes are stored in YAML format; gbdes uses the Python code pixmappy (ascl:2210.012) to read the astrometric solution files and execute specified transformations.
pixmappy provides a Python interface to gbdes pixel map (astrometry) solutions. It reads the YAML format astrometry solutions produced by gbdes (ascl:2210.011) and issues a PixelMap instance, which is a map from one 2d coordinate system ("pixel") to another ("world") 2d system. A PixelMap instance can be used as a function mapping one (or many) coordinate pairs. An inverse method does reverse mapping, and the local jacobian of the map is available also. The type of mapping that can be expressed is very flexible, and PixelMaps can be compounded into chains of tranformations.