Fast and precise center location for circle target of CCD laser autocollimator

To meet the requirements for measuring accuracy and real-time performance of charge coupled device (CCD) laser autocollimators in fields of high-accuracy metrology and aiming and tracing system, a fast and precise center location method for circle target of CCD laser autocollimator is proposed. The specific characteristics of the circle target edge are fully extracted by using multiple structuring elements-based generalized morphological edge detection, while the influences of the noises in images are diminished. Then, the edge is quickly located in subpixel precision by adopting the polynomial interpolation method, and the center position of the circle target is acquired accurately by using circle fitting method based on least square fitting method. Experimental results show that the proposed method is fast, stable and accurate, and the measuring accuracy of the modified CCD laser autocollimator is improved from 2 arcsec to ± 0.25 arcsec in 0.23s (a single measurement process). The proposed method can efficiently fulfill the requirements for high accuracy and real-time performance of CCD laser autocollimators in small angle measuring and tracing systems.