The AAO has six measuring machines for analysing photographic plates and films. Two of these are located at the Epping laboratory along with the archive of AAT prime focus plates, and four are on Siding Spring mountain (two at the Schmidt telescope and two at the AAT). Whilst all these machines can be used as accurate XY measuring engines, only the PDS can be used to digitize the plate and extract the density (intensity) information. The PDS also yields the most accurate positions, and should be used for determining target positions for AUTOFIB from Schmidt plates.
NOTE: The advent of large scanning machines (eg. COSMOS and APM) and the publicly available catalogues they have produced (eg COSMOS and APM southern sky catalogues, STScI Guide Star Catalog and the STScI Digital Sky Survey) has meant that the demand for scanning and position measurement at the AAO has fallen off in recent years. The PDS is currently in-operable, and there seems to be little community desire to resurrect it.
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