High-resolution surface shape measurement of parabola antenna reflector by using grating projection method with virtual targets

Abstract

In this study, a high-resolution surface shape measurement system incorporating a grating projection method and a virtual-target registration method is constructed as inspection tools for precise large space structures, and the applicability of the constructed measurement system is discussed for a parabola antenna reflector with a diameter of 1.5 m. Partial surfaces of the parabola antenna reflector are initially measured by photogrammetry by using a grating projection method. The full-field surface of the parabola antenna reflector is subsequently reconstructed by merging the measured partial shape data using a virtual-target registration method. The virtual-target registration method applies feature-point matching of the virtual targets to calculate a coordinate transformation matrix that serves as an interface between two sets of the dense 3D point cloud data, and thus it can precisely connect the partial shape data even if any physical corresponding points or any signature shapes are not included in the overlap region of the connected data. The result shows that the partial surfaces of the parabola antenna reflector are successfully captured by the photogrammetry by using the grating projection method with an accuracy of 0.17 mm RMS and spatial resolution of 0.35 mm and are precisely merged by the virtual-target registration method with the same order of measurement accuracy. The validity of the reconstructed surface shape of the parabola antenna reflector is then confirmed by comparing the measurement results of the commercial photogrammetric measurement system using coded targets. The result clearly indicates that the constructed measurement system allows visualization of the intricate local surface as well as the global surface of the parabola antenna reflector with a high spatial resolution, and this cannot be achieved with a traditional photogrammetric measurement system by using the attached targets. The study offers an effective high-resolution non-contact surface shape measurement system for large space structures.