Research on accuracy testing of close-range photogrammetry for geometric feature measurement in particle accelerator

Abstract To meet the needs of the Hefei Advanced Light Facility project and reasonably use the close-range photogrammetric system in future alignment work. The research on the method and accuracy of the Aicon DPA close-range photogrammetry system for geometric element measurement was carried out. Using the external consistency and the internal consistency as evaluation indexes, the systems are designed and built with the laser interferometer (XL80), laser tracker (AT 960), standard tetrahedral and marble guide to test the point coordinates, distance, flatness measurement accuracy and measurement repeatability for geometric element measurement accuracy. The experimental results show that Aicon DPA point coordinates, distance, and flatness measurements have high accuracy in close-range photogrammetry. The point coordinate and flatness measurements are 9.5 μm and 5.4 μm, respectively, equal to or even better than the laser tracker's measurement results. Furthermore, the measurement repeatability is better than 5 μm. The results of the simulated engineering site show that the Aicon DPA has an accuracy of 19.8 μm, maintaining high accuracy and good immunity to environmental interference. With the expansion of the photogrammetry control range, when the length reference is shorter than the measured object, the measurement accuracy will continue to decrease. But when using the length data of the interferometer as a reference, the accuracy within 8 meters can be better than 30 μm. The accuracy testing process and conclusion of this article have reference values for the use of close-range photogrammetry systems in particle accelerators. The close-range photogrammetry system will be fully utilized in alignment work such as geometric element measurement, deformation monitoring and data fusion with laser trackers in the Hefei Advanced Light Facility.