Precise center location algorithm for circle target in CCD laser dual axis autocollimator

A precise circle target center location algorithm was proposed and the multiscale generalized mathematical morphological filtering method with multiple structuring elements was utilized for eliminating noise in the image. The subpixel position of circle target was obtained by Zernike moment contour subpixel location algorithm, and the circle target center position was acquired ultimately and accurately using circle fitting method based on least square method. The experiment results show that the method is stable and accurate located for measuring 2D small angle, and the measuring uncertainty of this modified instrument is better than 0.3″ within ±2′ range, with the measuring resolution increased by 10 times. The results also show that the measuring resolution and accuracy of the autocollimator can be improved effectively.