Subpixel grid coordinates using line following filtering

Subpixel grid coordinates using line following filtering. A line following filter is proposed, which determines the center coordinates of a line with subpixel accuracy. If the line is strongly curved, a systematic error must be corrected using a calibration function. Applied to a cross grating it yields the cross coordinates by intersection of two bands of lines, which first are smoothed by spline approximation. The method is applied to 2D- and 3D-deformation of cross gratings fixed on the surface of metallic specimens.