Abstract: The instant invention is a method and apparatus for the measurement, with low uncertainty, of the six degrees of freedom of a first structure relative to a second structure. The apparatus is comprised of compact, rigid, thermally stable structures. The invention uses linear displacement transducers which have no active pointing to maintain a desired orientation of the linear displacement transducers with other parts of the measurement system.

Abstract: Interferometric apparatus and methods for reducing the effects of coherent artifacts in interferometers. Fringe contrast in interferograms is preserved while coherent artifacts that would otherwise be present in the interferogram because of coherent superposition of unwanted radiation generated in the interferometer are suppressed. Use is made of illumination and interferogrammetric imaging architectures that generate individual interferograms of the selected characteristics of a test surface from the perspective of different off-axis locations of illumination in an interferometer and then combine them to preserve fringe contrast while at the same time arranging for artifacts to exist at different field locations so that their contribution in the combined interferogram is diluted.