PDS在天体测量中的应用技术

APPLIED TECHNIQUES OF PDS IN PHOTOGRAPHIC ASTROMETRY

本文对数字像定中心算法作了适当改进,并且通过试验,提出了扫描参数选择的定量依据。

In the algorithm of the digital image centering, in fact, even though results of the one-dimensional fitting are adopted as initial values of parameters in the two-dimensional fitting, the iterations of the nonlinear least-square process with Newton's method for the later fitting may not converge for some fainter or poorer images. This algorithm is modi-fied by means of the Fletcher-Powell's method in this paper, which reduces the require-ments for precisions of the initial values, so that the one-dimensional fitting is no longer necessarv, and the computer time is economized and the convergence is improved. The quantitative examinations for the scan parameter selecting indicate that diffarent sizes of sampling aperture with range of 10×10-50×50 square μm do not affect the astro-metric precision and that Ax and Ay should be the same in size as the sampling aperture. The selection of these parameters should, therefore, mainly ensure that there are enough pixels in the image area. The examinations also show that the R and F scan types are better than the E. For the former two types' the higher scan speed can be used (up to 20 mm/ sec), and the astrometric precision does not reduce. However, in consideration of si-gnificantly increased fitting errors in high speed scan, the low or intermediate (about 5 mm/sec or lower) speeds should generally be used.