Citation: Puerto, P.; Heißelmann, D.; Müller, S.; Mendikute, A. Methodology to Evaluate the Performance of Portable Photogrammetry for Large-Volume Metrology. Metrology 2022, 2, 320–334. https://doi.org/10.3390/ metrology2030020 Academic Editors: Stephen Kyle, Stuart Robson and Ben Hughes Received: 31 March 2022 Accepted: 22 June 2022 Published: 28 June 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). Article Methodology to Evaluate the Performance of Portable Photogrammetry for Large-Volume Metrology Pablo Puerto 1, * , Daniel Heißelmann 2 , Simon Müller 3 and Alberto Mendikute 1, * 1 IDEKO, Basque Research and Technology Alliance (BRTA), 20870 Elgoibar, Spain 2 Physikalisch-Technische Bundesanstalt (PTB), 38106 Braunschweig, Germany; daniel.heisselmann@ptb.de 3 Physikalisch-Technische Bundesanstalt (PTB), Technische Universität Braunschweig, 38100 Braunschweig, Germany; sim.mueller@tu-braunschweig.de * Correspondence: ppuerto@ideko.es (P.P.); amendikute@ideko.es (A.M.); Tel.: +34-943-748-000(P.P. & A.M.) Abstract: The increased relevance of large-volume metrology (LVM) in industrial applications entails certain challenges: measurements must be cost-efficient and the technologies must be easy to use while ensuring accuracy and reliability. Portable photogrammetry shows great potential to overcome such challenges, but industrial users do not yet rely on its accuracy for large scenarios (3 to 64 m), especially when mass-market cameras are not conceived of as industrial metrology instruments. Furthermore, the measurement results might also depend on the operator’s skills and knowledge of the key process variables. In this work, a methodology was designed so that the measurement uncertainty of portable photogrammetry can be evaluated under controlled conditions for LVM. To do so, PTB’s reference wall, which was designed to assess laser-based methods applied to large volumes, was used as a reference artefact to study the measurement performance under different conditions, enabling an analysis of the relative influence of two process variables: the spatial arrangement of the optical instruments on the scene, and the relative camera poses for an accurate triangulation. Ac- cording to these variables, different measuring conditions were designed (Monte Carlo analysis), and experimentally evaluated and reported (LME, length measuring errors), analysing the performance figures expected from both unskilled and expert users. Keywords: large-volume metrology (LVM); portable photogrammetry; path planning; inline measurement 1. Introduction In industries such as aerospace, capital goods, energy, and general engineering, mea- suring objects with large volumes (above 3 m 3 ) and a high level of accuracy (better than +/−0.1 mm/m, coverage factor k = 1) [1] is a challenging undertaking. Because these indus- tries require a reliable measurement technology, measuring systems based on laser trackers (LTs) or on interferometry are usually used. For example, LT technology, in which a laser beam is reflected in a designated spherically mounted retroreflector (SMR), can achieve low measurement uncertainties for large volumes. The main feature of SMRs is their ability to reflect light in the direction of the incoming beam independently of the relative orientation. Moreover, ISO 10360-10:2021 encourages the use of laser trackers because it describes how to determine the accuracy of the given system under restrictive conditions. Furthermore, the integration of LTs into metrological software allows the achievable uncertainty to be predicted in such a way that users can better plan measurements to ensure they are of high quality [2]. Several approaches focus on further optimising measurement uncertainty and process efficiency using LTs, such as multi-lateration [3–5] and multi-sensor architec- tures [6,7]. However, a measuring process based on LTs entails several challenges: the significant costs of the equipment, the high mechanical stability requirements over the observation period, and the need for highly experienced operators [8,9]. Metrology 2022, 2, 320–334. https://doi.org/10.3390/metrology2030020 https://www.mdpi.com/journal/metrology