Re-calibration of GSC2.3 with UCAC2

To make GSC-II more accurate and useful, it is necessary to re-calibrate GSC-II when a better reference catalogue (UCAC2) is available. With UCAC2 as the reference, preliminary re-calibration of some sample plates from GSC2.3 were carried out with different methods, such as Global, Mask and Filter. The results indicate that a 7th-order polynomial is sufficient to account for the influence of Schmidt plate deformation on the measured coordinates of stars. The magnitude equation can be eliminated after correcting for a common magnitude equation. The RMS of the re-calibrated data is around ±0.2~0.3 arcsec.