SUBPIXEL GRID COORDINATES USING LINE FOLLOWING FILTERING

A line following filter is proposed, which determines the center coord inates of a line with subpixel accuracy. If the line is strongly curve d, a systematic error must be corrected using a calibration function. Applied to a cross grating it yields the cross coordinates by intersec tion of two bands of lines, which first are smoothed by spline approxi mation. The method is applied to 2 D- and 3 D-deformation of cross gra tings fixed on the surface of metallic specimens.