Reconstruction of small components using photogrammetry: a quantitative analysis of the depth of field influence using a miniature step gauge

In this work, authors investigated the effect of the Depth of Field (DoF) reduction, arising when the acquisition of small objects is carried out with a photogrammetry-based system using a Digital Single Lens Reflex (DSLR) camera and the structure from motion (SfM) algorithm. This kind of measuring instrument is very promising for industrial metrology according to the paradigms of the fourth industrial revolution. However, when increasing the magnification level, necessary for the reconstruction of sub-millimetric features, there is a corresponding decrease of the DoF, leading to possible effects on the reconstruction accuracy. Thus, the effect of the DoF reduction was analysed through the reconstruction of a well-known artefact: the step gauge. The analysis was conducted considering the theory behind the DoF concept, the analysis of the 2D images, input of photogrammetric reconstruction and, finally, the results in terms of dimensional verification of the reconstructed step gauge.