Astrometry:
The astrometry of the GSC II is based
on a two step process. First all the plates are individually reduced
using a quadratic polynomial solution. Second, systematics that
are common to a set of plates were removed. The reference catalogs
used were with ACT and the Tycho Catalog II.
Photometry:
The photometric calibration is based on a Chebyshev polynomial fit
to sequence stars from the GSPC
2 and the Tycho
Catalog for the bright end.
Classification:
Objects in the GSC II are classified
as stars or nonstars. Nonstars may be either galaxies,
or blended objects with overlapping images on the Schmidt source
plate material. Classification was performed using a set of oblique
decision trees generated using the OC1
algorithm. Thirty classification features were used, and the
features were ranked
before use in order to compensate for plate-to-plate variations.
Final classification was determined by a vote of classifications
from overlapping plates.
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