A major goal was to make the calibration algorithms dependent only on these data structures and not on the details of a particular file format. The structure of the FITS file for both instruments is shown below. The primary header contains only those keywords that apply to all the FITS extensions contained in the file. A number of basic ANSI C data structures have been defined to correspond to the data files described above. It has both first order and Echelle gratings, with a wide variety of apertures ranging from large imaging apertures to long slits to short Echelle slits.
Images can be full frame, binned, or a subset of the full frame.
MAMA data can be taken either in accumulate or time-tag mode. The computation of the expected error of each pixel of the data products is an integral part of the pipeline processing at every stage as is keeping a record of data quality for each pixel. STIS data are associated for three purposes. Calstis adds together the CR-split exposures prior to flat fielding, with cosmic rays excluded from the sum. Repeatobs data are maintained as separate exposures, though calstis does also add them together.