PTB?s enhanced stitching approach for the high-accuracy interferometric form error characterization of spheres

The stitching procedure that was presented a few years ago allowed the reconstruction of the real shape of a sphere from the measured data that had been acquired by the sphere interferometer of the Physikalisch-Technische Bundesanstalt. The enhancements described in this paper involve additional information from the measurements that could not be taken into account before. Therefore, not only the determination of the uncertainty of the reconstructed results is enabled, but also the occurrence of large-scale systematic deviations can be prevented. As a consequence, the form deviations of a sphere can be characterized reliably, which benefits the efforts of reducing the form deviations of the silicon spheres of the Avogadro project. In other fields where spheres are used as references, accurate knowledge of the real form may be helpful for further improvements.