Uncertainty model for a traceable stereo-photogrammetry system

Abstract

Through the computational modelling and experimental verification of a stereo-photogrammetry system, the expanded uncertainty on form measurement was estimated and was found to be 32μm, 12μm and 29μm for a 95% confidence interval (coverage factors of k = 3.2, 2.0 and 2.0 respectively) in the x, y and z axis respectively. The contribution of systematic offsets in the system properties was also investigated, demonstrating the complex distortions of the measurement volume that result from these systematic errors. Additionally, a traceable method of applying a scale factor to the reconstruction was demonstrated using a laser interferometer and gauge block. The relative standard uncertainty on the size of the measurements was estimated to be 0.007% corresponding to length measurement uncertainties of around 7μm over a 100 mm range. Finally, the residuals from a linear fit of the scale factor were found to exhibit behaviour that would be expected to result from small offsets in the system properties. The outcome of this work is a better understanding of the propagation of uncertainty through the stereo-photogrammetry system as well as highlighting key influence factors that must be addressed in future work.