Metrology

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38 pages, 11665 KB

Open AccessArticle

Eccentricity Correction Methods for Circular Targets in Perspective Projection

by Frank Liebold and Hans-Gerd Maas

Metrology 2026, 6(2), 28; https://doi.org/10.3390/metrology6020028 - 20 Apr 2026

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In a perspective projection, a circular target appears as an ellipse for an oblique view. Herein, the ellipse center obtained from image coordinate measurement operators differs from the projection of the circle center. This discrepancy is called eccentricity and may lead to systematic [...] Read more.

In a perspective projection, a circular target appears as an ellipse for an oblique view. Herein, the ellipse center obtained from image coordinate measurement operators differs from the projection of the circle center. This discrepancy is called eccentricity and may lead to systematic errors. This article documents the significance of these discrepancies and discusses five different correction methods that can be applied in the image space or as a model adaptation. Two of the methods include the determination of the circle radius and thus also offer a possibility to define the scale. The eccentricity correction procedures are validated in a series of experiments, which proved that even extreme eccentricity effects can be fully compensated. In the experiment on the approaches including scale determination, the precision and accuracy of the scale definition is investigated, obtaining relative accuracies of 0.5–1%. Full article

(This article belongs to the Special Issue Advances in Optical 3D Metrology)

25 pages, 3415 KB

Open AccessArticle

Quantifying the Performance of Distributed Large-Volume Metrology Systems for Dynamic Measurements: Methodology Development

by David Gorman, Claire Pottier, Marta Cibrian and Samual Johnston

Metrology 2026, 6(1), 7; https://doi.org/10.3390/metrology6010007 - 30 Jan 2026

Viewed by 647

Abstract

Limitations associated with traditional automation approaches within manufacturing have driven the pursuit of more flexible and intelligent robot guidance methods. One promising development in this area is the integration of external multitarget six degrees of freedom (6 DoF) distributed large-volume metrology (DLVM) into [...] Read more.

Limitations associated with traditional automation approaches within manufacturing have driven the pursuit of more flexible and intelligent robot guidance methods. One promising development in this area is the integration of external multitarget six degrees of freedom (6 DoF) distributed large-volume metrology (DLVM) into the control loop. Although multiple standards exist across dimensional metrology, motion tracking, indoor positioning, robot guidance, and machine tool accuracy, there is no harmonised, technology-agnostic standard that fully encompasses the unique challenges of 6 DoF DLVM systems for dynamic applications. This work identifies key gaps in the current standards’ landscape and presents a technology-agnostic candidate test methodology intended to support future standardisation of dynamic DLVM performance evaluation. The method provides a metrologically grounded spatial reference path and a temporal alignment strategy so that position and orientation errors can be reported in the intrinsic coordinates of the path. The paper covers the basic principle of the test, artefact construction, synchronisation strategies, preliminary error modelling, and a baseline uncertainty approach, and reports representative results from initial prototype trials on a multi-nodal distance-camera DLVM system. The prototype results demonstrate feasibility and highlight temporal sampling and traceable timing as current limiting factors for fully deconvolving latency and pose error; these aspects are therefore positioned as instrumentation requirements and the focus of ongoing work. Full article

(This article belongs to the Special Issue Advances in Optical 3D Metrology)

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22 pages, 6841 KB

Open AccessArticle

Constraint-Aware Design of Spherical Camera Rigs for Optical Metrology

by Haider Ali Hasan, Ali Noori Abdulrasool, Hadeel Raad Mahdi and Bashar Alsadik

Metrology 2026, 6(1), 2; https://doi.org/10.3390/metrology6010002 - 7 Jan 2026

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Abstract

This paper introduces a constraint-aware optimization framework for designing spherical multi-camera rigs that achieve complete panorama coverage while adhering to physical and field-of-view limitations. The approach assesses coverage using solid-angle geometry and calculates the sampling density in pixels per steradian, providing a measurable, [...] Read more.

This paper introduces a constraint-aware optimization framework for designing spherical multi-camera rigs that achieve complete panorama coverage while adhering to physical and field-of-view limitations. The approach assesses coverage using solid-angle geometry and calculates the sampling density in pixels per steradian, providing a measurable, traceable basis for panoramic optical measurement. By viewing panoramic imaging as a directional measurement challenge, the framework aligns with principles of optical metrology and guarantees uniform, non-contact optical sensing around the sphere. The optimization process includes capsule-based collision constraints, soft coverage losses, and field-of-view intersection modeling to produce physically feasible rig configurations. Experiments show that the optimized rigs provide improved coverage uniformity and less redundancy, with validation through Blender-generated synthetic panoramas confirming the practical performance of the designed optical systems. The proposed approach allows for systematic, measurement-driven design of spherical camera rigs for use in immersive imaging, robotic perception, and structural inspection. Full article

(This article belongs to the Special Issue Advances in Optical 3D Metrology)

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21 pages, 7944 KB

Open AccessArticle

Estimation of Surface Normals of Aerospace Fasteners from 3D Terrestrial Laser Scanner Point Clouds

by Kate Pexman, Stuart Robson and Hannah Corcoran

Metrology 2025, 5(4), 68; https://doi.org/10.3390/metrology5040068 - 9 Nov 2025

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Abstract

Measurement systems such as laser trackers and 3D imaging systems are being increasingly adopted across the manufacturing industry. These metrology technologies can allow for live, high-precision measurement in a digital system, enabling the spatial component of the digital manufacturing twin. In aircraft wing [...] Read more.

Measurement systems such as laser trackers and 3D imaging systems are being increasingly adopted across the manufacturing industry. These metrology technologies can allow for live, high-precision measurement in a digital system, enabling the spatial component of the digital manufacturing twin. In aircraft wing manufacturing, drilling and fastening operations must be guided by precise measurements from a digital design model. With thousands of fasteners on each aircraft wing, even small errors in alignment of surface covers to wing ribs and spars can impact component longevity due to aerodynamic drag. Determining surface conformance of airstream-facing surfaces is currently largely performed though manual gauge checking by human operators. In order to capture the surface details and reverse engineer components to assure tolerance has been achieved, laser scanners could be utilised alongside a precise registration strategy. This work explores the quality of the aerostructure surface in a captured point cloud and the subsequent accuracy of surface normal determination from planar fastener heads. These point clouds were captured with a reference hand-held laser scanner and two terrestrial laser scanners. This study assesses whether terrestrial laser scanners can achieve <0.5° surface normal accuracy for aerospace fastener alignment. Accuracy of the surface normals was achieved with a nominal mean discrepancy of 0.42 degrees with the Leica RTC360 3D Laser Scanner (Leica Geosystems AG, Heerbrugg, Switzerland) and 0.27 degrees with the Surphaser 80HSX Ultra Short Range (Basis Software Inc., Redmond, WA, USA). Full article

(This article belongs to the Special Issue Advances in Optical 3D Metrology)

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19 pages, 1624 KB

Open AccessArticle

Uncertainty in Dimensional Measurements During Open-Die Forging

by Marco Tarabini

Metrology 2025, 5(3), 55; https://doi.org/10.3390/metrology5030055 - 2 Sep 2025

Cited by 1 | Viewed by 1479

Abstract

Integrating optical metrology into steelmaking and metalworking processes faces challenges not only from harsh conditions but also from a limited understanding of metrology concepts. The literature often overlooks distinctions between different uncertainty sources. This paper proposes a model for the quantification of uncertainty [...] Read more.

Integrating optical metrology into steelmaking and metalworking processes faces challenges not only from harsh conditions but also from a limited understanding of metrology concepts. The literature often overlooks distinctions between different uncertainty sources. This paper proposes a model for the quantification of uncertainty in dimensional measurements of open-die forged components, addressing the different uncertainty sources related to the measurand variability, to the instrumental uncertainty and to the definitional uncertainty. Guidelines for their evaluation are provided, and two case-studies related to measurement of forged shafts are presented and discussed. Full article

(This article belongs to the Special Issue Advances in Optical 3D Metrology)

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16 pages, 5307 KB

Open AccessArticle

Revisiting an Indentation Method for Measuring Low Wear Rates Using 3D Interferometry

by Gabriela R. Piazzetta, Thomas M. Zeller, Juan M. Hernandez-Otalvaro and Giuseppe Pintaude

Metrology 2025, 5(2), 35; https://doi.org/10.3390/metrology5020035 - 8 Jun 2025

Cited by 1 | Viewed by 1810

Abstract

Predicting the wear of disc cutters in Tunnel Boring Machines (TBMs) is a complex challenge due to the large scale of the machinery and the numerous operational variables involved. Laboratory-scale tests offer a controlled approach to isolating and analyzing specific wear mechanisms. However, [...] Read more.

Predicting the wear of disc cutters in Tunnel Boring Machines (TBMs) is a complex challenge due to the large scale of the machinery and the numerous operational variables involved. Laboratory-scale tests offer a controlled approach to isolating and analyzing specific wear mechanisms. However, the extremely low wear rates observed in such simulations pose challenges for conventional characterization methods, as gravimetric and profilometric techniques often lack the precision and accuracy needed to measure low wear patterns with an uneven morphology. To address this, this study revisited a methodology for quantifying low wear rates in a reciprocating wear test using AISI H13 tool steel disc cutters. This approach integrates spherical indentation marks as reference points with 3D white-light interferometry, enabling high-precision material loss measurements. Eighteen disc samples were subjected to wear testing, with 3 indentations analyzed per sample, for a total of 54 indentations. The statistical validation confirmed the method’s reproducibility and reliability. The proposed approach provides a robust alternative to existing techniques, addressing a critical gap regarding the accurate quantification of low wear rates in controlled laboratory settings. Full article

(This article belongs to the Special Issue Advances in Optical 3D Metrology)

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35 pages, 14662 KB

Open AccessArticle

A Statistical Approach for Characterizing the Behaviour of Roughness Parameters Measured by a Multi-Physics Instrument on Ground Surface Topographies: Four Novel Indicators

by Clément Moreau, Julie Lemesle, David Páez Margarit, François Blateyron and Maxence Bigerelle

Metrology 2024, 4(4), 640-672; https://doi.org/10.3390/metrology4040039 - 18 Nov 2024

Cited by 3 | Viewed by 3264

Abstract

With a view to improve measurements, this paper presents a statistical approach for characterizing the behaviour of roughness parameters based on measurements performed on ground surface topographies (grit #080/#120). A S neox^TM (Sensofar^®, Terrassa, Spain), equipped with three optical instrument [...] Read more.

With a view to improve measurements, this paper presents a statistical approach for characterizing the behaviour of roughness parameters based on measurements performed on ground surface topographies (grit #080/#120). A S neox^TM (Sensofar^®, Terrassa, Spain), equipped with three optical instrument modes (Focus Variation (FV), Coherence Scanning Interferometry (CSI), and Confocal Microscopy (CM)), is used according to a specific measurement plan, called Morphomeca Monitoring, including topography representativeness and several time-based measurements. Previously applied to the Sa parameter, the statistical approach based here solely on the Quality Index (QI) has now been extended to a multi-parameter approach. Firstly, the study focuses on detecting and explaining parameter disturbances in raw data by identifying and quantifying outliers of the parameter’s values, as a new first indicator. This allows us to draw parallels between these outliers and the surface topography, providing reflection tracks. Secondly, the statistical approach is applied to highlight disturbed parameters concerning the instrument mode used and the concerned grit level with two other indicators computed from QI, named homogeneity and number of modes. The applied method shows that a cleaning of the data containing the parameters values is necessary to remove outlier values, and a set of roughness parameters could be determined according to the assessment of the indicators. The final aim is to provide a set of parameters which best describe the measurement conditions based on monitoring data, statistical indexes, and surface topographies. It is shown that the parameters Sal, Sz and Sci are the most reliable roughness parameters, unlike Sdq and S5p, which appear as the most unstable parameters. More globally, the volume roughness parameters appear as the most stable, differing from the form parameters. This investigated point of view offers thus a complementary framework for improving measurement processes. In addition, this method aims to provide a global and more generalizable alternative than traditional methods of uncertainty calculation, based on a thorough analysis of multi-parameter and statistical indexes. Full article

(This article belongs to the Special Issue Advances in Optical 3D Metrology)

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13 pages, 9589 KB

Open AccessArticle

Metrological Analysis with Covariance Features of Micro-Channels Fabricated with a Femtosecond Laser

by Matteo Verdi, Federico Bassi, Luigi Calabrese, Martina Azzolini, Salim Malek, Roberto Battisti, Eleonora Grilli, Fabio Menna, Enrico Gallus and Fabio Remondino

Metrology 2024, 4(3), 398-410; https://doi.org/10.3390/metrology4030024 - 1 Aug 2024

Viewed by 2339

Abstract

This study presents an automated methodology for evaluating micro-channels fabricated using a femtosecond laser on stainless steel substrates. We utilize 3D surface topography and metrological analyses to extract geometric features and detect fabrication defects. Standardized samples were analyzed using a light interferometer, and [...] Read more.

This study presents an automated methodology for evaluating micro-channels fabricated using a femtosecond laser on stainless steel substrates. We utilize 3D surface topography and metrological analyses to extract geometric features and detect fabrication defects. Standardized samples were analyzed using a light interferometer, and the resulting data were processed with Principal Component Analysis (PCA) and RANSAC algorithms to derive channel characteristics, such as depth, wall taper, and surface roughness. The proposed method identifies common defects, including bumps and V-defects, which can compromise the functionality of micro-channels. The effectiveness of the approach is validated by comparisons with commercial solutions. This automated procedure aims to enhance the reliability and precision of femtosecond laser micro-milling for industrial applications. The detected defects, combined with fabrication parameters, could be ingested in an AI-based process to optimize fabrication processes. Full article

(This article belongs to the Special Issue Advances in Optical 3D Metrology)

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