The subaperture stitching technique requires the registration of freeform subapertures into global coordinate frame beforestitching in order to compute entire freeform wavefront. A scanning Shack-Hartman Sensor (SHS) utilizes translationstages to scan the freeform surface in XY plane and measure the slope data of various subapertures. The measured slopedata is then integrated using weighted cubic spline (WCSLI) based integration method to compute the phase data. Thepositioning error during scanning causes misalignments between the measured subapertures and their nominal values.The least square based subaperture stitching methods are not capable to minimize lateral misalignment errors of freeformsubapertures and therefore degrade the performance of subaperture stitching process. In this work, we have utilizedfiducial added planes for correction of angular and rotation misalignments of an extended cubic phase plate. An intrinsicsurface feature (ISF) based registration method is used for lateral misalignment corrections. Gaussian curvature is usedas an intrinsic pattern which can be defined as one of the fundamental second order geometric properties of a surface.Any shift in the peaks of the Gaussian curvature of reference and measured subaperture corresponds to lateralmisalignments in X and Y directions and need to be minimized before registration of subaperture into global frame ofreference. After precise registrations, all the subapertures are stitched with consistent overlapping area by using leastsquare fitting method. A numerical validation of the proposed scheme is carried out which demonstrates the effectivenessof the proposed method to improve the subaperture stitching accuracy.
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