The influence of software algorithms on photogrammetric micro-feature measurement’s uncertainty

In the 3D reconstruction field, photogrammetry is a powerful and robust measurement technology for lots of dimensional ranges, from macro and aerial photogrammetry to close-range and micro-photogrammetry, emerging recently with good results also in the survey of small object with sub-millimeter features. A fundamental issue is still the calibration, for the estimation of both internal and external parameters, mostly in the case of very small dimensional ranges. In previous works, some aspects of the photogrammetric process have been taken into account and analyzed by 3D comparisons with a reference model, while the present work is firstly focused on the outputs of the camera’s alignment phase, in which the computation of internal and external parameters is carried out. By repetition of the process in the same conditions, it has been noticed that alignment results, in terms of camera coordinates and internal calibration parameters, are affected by a sort of variability. Thus, the aim of this work is to estimate the uncertainty component over the 3D reconstruction accuracy attributable to the repeatability of the photogrammetric software. For this purpose, several factors, linked to the shooting geometry and to the alignment process, have been considered.