Three-dimensional Measurement Technique Research Articles

Three 1-bit speckle-embedded pulse-width modulation patterns for robust absolute 3D measurement

In three-dimensional (3D) shape measurement techniques using structured light, 1-bit pulse-width modulation (PWM) patterns and 1-bit speckle patterns can be projected at high speed. However, when combining PWM and speckle patterns to integrate their advantages, the decoupling problem is insurmountable. In this work, a novel 1-bit speckle-embedded PWM (SPPWM) method was proposed to achieve absolute 3D shape measurement using only three binary patterns. Our method consists of three main steps: First, a sinusoidal pattern reconstruction network was proposed to eliminate the high-order harmonics and speckle patterns in the SPPWM patterns and obtain high-quality sinusoidal patterns. Second, a multi-temporal spatial correlation matching algorithm was proposed to obtain a coarse disparity map from the three SPPWM patterns. Third, the high-accuracy wrapped phase map is used as an additional constraint for refining the coarse disparity map to obtain the final high-accuracy disparity map for absolute 3D measurement without phase unwrapping. Our method combines the advantages of fringe projection profilometry techniques for high-precision wrapped phase retrieval and speckle correlation matching algorithms for robust and unambiguous disparity map calculation. The experimental results demonstrated that our method could realize high-precision absolute 3D shape measurement with an accuracy of 0.057 mm using only three 1-bit SPPWM patterns. Furthermore, different simulation noises were used to demonstrate the robustness of the proposed method.

Three-dimensional shape measurement technique for hot and shiny forging

For hot and shiny forging, rapid optical three-dimensional (3D) shape measurement can find the defects in time, improve manufacturing efficiency and reduce manufacturing cost. Optical 3D measurement of hot and shiny forging faces following three challenges. (a) Influence of blackbody radiation on the red band of visible light leads to saturation of captured fringe pattern. (b) Infrared band of blackbody radiation causes the camera to heat up. (c) Specular reflection of shiny forging leads to local saturation of captured fringe pattern. To address the above issues, we propose an effective optical 3D measurement scheme for hot and shiny forging in this paper. Firstly, the experiments demonstrate that the influence of blackbody radiation on visible light is concentrated in red light band and has no crosstalk in the blue light band, so we adopt blue light projection and blue light band-pass filter (BBF) to capture clear fringe pattern. Secondly, since the BBF cannot block the near-infrared component, we use an infrared light cutoff filter (ICF) to reduce the thermal effect of blackbody radiation. Finally, we analyze the Fourier transform (FT) spectrum of saturated fringe pattern caused by specular reflection, and propose an efficient Butterworth low-pass filtering (BLPF) method that does not require additional hardware, algorithm processing, and image assistance. The experimental results verify the effectiveness of the proposed scheme.

Three-dimensional deformation measurement techniques in space multi-physical fields based on digital image correlation

Aiming at the three-dimensional deformation measurement requirement of the high-stability structure of spacecraft in space multi-physical fields, a comprehensive instrument protection device in a vacuum high-low temperature environment is developed using ultra-low temperature anti-condensation and vacuum heat insulation technology. This ensures that the digital image correlation (DIC) measurement camera always remains in a constant temperature and pressure environment and can stably exert its original efficiency in space multi-physical field environments. Subsequently, a path-dependent DIC method based on a graphics processing unit computing parallel acceleration is proposed by combining a pre-interpolation strategy and integrated image technology, which realizes high-precision matching of digital images before and after deformation in a spatial multi-physical field environment and improves the computing efficiency. To address the problem that a common reference point may deform significantly in a space environment with a large temperature change, which leads to inaccurate system accuracy, combined with a random sampling consistency algorithm and singular value decomposition method, the optimal registration of the coordinate system and the solution of deformation were realized by setting the threshold of the reference point margin screening. Finally, a three-dimensional deformation measurement system in high- and low-temperature vacuum environments was built, and the three-dimensional deformation measurement of the satellite antenna in high- and low-temperature vacuum environments was verified, which proves the effectiveness and accuracy of the above method.

From 2D to 3D: automatic measurement of the Cobb angle in adolescent idiopathic scoliosis with the weight-bearing 3D imaging

Background contextAdolescent idiopathic scoliosis (AIS) necessitates accurate spinal curvature assessment for effective clinical management. Traditional two-dimensional (2D) Cobb angle measurements have been the standard, but the emergence of three-dimensional (3D) automatic measurement techniques, such as those using weight-bearing 3D imaging (WR3D), presents an opportunity to enhance the accuracy and comprehensiveness of AIS evaluation. PurposeThis study aimed to compare traditional 2D Cobb angle measurements with 3D automatic measurements utilizing the WR3D imaging technique in patients with AIS. Study design/settingA cohort of 53 AIS patients was recruited, encompassing 88 spinal curves, for comparative analysis. Patient sampleThe patient sample consisted of 53 individuals diagnosed with AIS. Outcome measuresCobb angles were calculated using the conventional 2D method and three different 3D methods: the Analytical Method (AM), the Plane Intersecting Method (PIM), and the Plane Projection Method (PPM). MethodsThe 2D cobb angle was manually measured by 3 experienced clinicians with 2D frontal whole-spine radiographs. For 3D cobb angle measurements, the spine and femoral heads were segmented from the WR3D images using a 3D-UNet deep-learning model, and the automatic calculations of the angles were performed with the 3D slicer software. ResultsAM and PIM estimates were found to be significantly larger than 2D measurements. Conversely, PPM results showed no statistical difference compared to the 2D method. These findings were consistent in a subgroup analysis based on 2D Cobb angles. ConclusionEach 3D measurement method provides a unique assessment of spinal curvature, with PPM offering values closely resembling 2D measurements, while AM and PIM yield larger estimations. The utilization of WR3D technology alongside deep learning segmentation ensures accuracy and efficiency in comparative analyses. However, additional studies, particularly involving patients with severe curves, are required to validate and expand on these results. This study emphasizes the importance of selecting an appropriate measurement method considering the imaging modality and clinical context when assessing AIS, and it also underlines the need for continuous refinement of these techniques for optimal use in clinical decision-making and patient management.

Research on the rapid 3D measurement of satellite antenna reflectors using stereo tracking technique

Measurement and analysis of surface accuracy are crucial steps in the manufacturing process of satellite antenna reflectors. The conventional close-range photogrammetry requires attaching target points on the surface, which is time-consuming and may damage the surface quality. To overcome these drawbacks, a rapid measurement technique of non-contact three-dimensional (3D) shapes is proposed, which is based on the integration of a stereo tracking method and a structured light measurement method. This paper focuses on addressing the issue of obtaining pose transformation matrices for measurement devices in motion within this method. Initially, a plane tracking scheme and tracking plate pattern is designed. Furthermore, the feature points of the tracking plate are extracted from the target area of image processing. Moreover, the pose transformation matrix of the tracking plate relative to the fixed world coordinate system at different positions is obtained using the triangulation method. Finally, a measurement experiment is conducted, resulting in a stereo tracking scheme error within 0.5%.

Crack recognition approach assisted by three-dimensional measurement technique

Crack recognition approach assisted by three-dimensional measurement technique

A robust method for multi-view 3D data stitching based on pasted marked points

High-precision three-dimensional (3D) measurement techniques commonly perform 3D point cloud data stitching using pasted marked points. However, pasted marked points exhibit a high degree of randomness and are susceptible to mismatching due to their structural similarity. Therefore, this paper presents a robust method for multi-view 3D data stitching based on pasted marked points (RMSM). First, potential matched marked point pairs (MMPP) are identified according to spatial feature invariance constraints, and a matching strength calculation model is established to find the fiducial point pairs. Then, a quick public MMPP searching algorithm using the congruent triangle search method is proposed. Thus, the problem of mismatching caused by structurally similar marked points can be eliminated, and robust stitching of 3D data from different views can be achieved. In simulation and measurement experiments, the RMSM demonstrates superior accuracy compared to alternative methods and holds promise for application in various multi-view 3D data stitching methodologies.

Color crosstalk compensation method for color phase-shifting fringe projection profilometry based on the phase correction matrix.

Color phase-shifting fringe projection profilometry is one of the single-shot three-dimensional shape measurement techniques. The color crosstalk of the projector-camera system yields undesired phase errors when using phase-shifting method. In this paper, a color crosstalk compensation method based on phase correction matrix is proposed. In this method, the phase correction matrix is established to compensate the deviations between the actual phase-shift values in the acquired fringes and the standard ones in the ideal fringes. Only two fringe patterns are utilized to obtain the phase correction matrix. The quadratic equations for calculating the actual phase-shift values of the fringes in the three color channels are derived. The actual phase-shift values and the corresponding standard ones are employed to form the equilibrium equations for computing the phase correction coefficients in the matrix. Experimental results demonstrate the feasibility of the proposed method and it can effectively reduce the induced overall phase error caused by the color crosstalk.

Adaptive chessboard-like high-frequency projection method for three-dimensional measurement of shiny surfaces

Abstract Shiny surface is challenging for the structured light fringe projection three-dimensional measurement technique, since the image saturation caused by highlight results in incorrect intensities in captured images of fringe patterns, and leads to serious phase errors and measurement errors. To address the issue, an adaptive chessboard-like high-frequency projection intensity adjustment technique is proposed. The proposed method alleviates image saturation by adaptively adjusting the intensity of the high-frequency chessboard-like projection pattern. And the complementary patterns are projected to suppress reflections and enhance the robustness of decoding. The experimental results demonstrate that the proposed method achieve high measurement accuracy for shiny surfaces.

Performance degradation of steel rebar considering corrosion spatial variability in concrete

The corrosion of steel bars is the main issue affecting the durability of reinforced concrete structures, which is nonuniform owing to the material properties and external environmental effects. In this study, the performance degradation of steel rebars in concrete is estimated considering corrosion spatial variability. With the aid of a three-dimensional measurement technique, a finite element model based on the scanning result was established to examine the corrosion effect on the tensile behaviour of the corroded bars, which was validated with the experimental results and digital image correlation observation. To assess the deformation behaviour of the corroded steels, a semi-analytical model was developed based on the cross-sectional area distribution and material properties. Subsequently, the spatial weight loss distributions with different degrees of corrosion were generated using a random field model. The model parameters were determined by combining engineering judgement and estimation of the experimental results. Finally, probabilistic model of degraded performance was established using the deterministic assessment and simulated steel weight loss distribution.

Reverse Engineering Used to Profile a Gerotor Pump Rotor

In most situations, for the proper design of a gerotor pump, numerous parameters must be taken into account: the pump geometry, the properties of the materials from which the pumps are made (Young’s modulus, Poisson’s coefficient, friction coefficients, etc.), the hydraulic characteristics of the circulated fluids (fluid density, kinematic viscosity, etc.), the working performance of the pump (speed ranges, pressure, flow rate, etc.), with greater or lesser influence on volumetric efficiency, work capacity, or energy consumption. The paper presents a study regarding the inspection of the reciprocally enwrapping surfaces of the gerotor pumps using a three-dimensional measurement technique specific to reverse engineering, which involves 3D scanning of the pump components in gearing movement. The components were measured by means of a specific software (GOM Inspect) and compared, by overlap, with the CAD models made with the help of CATIA software (CATIA V5R21). At the same time, an analytical calculation algorithm was developed for the complementarity of virtual representations. Finally, the advantages of the reverse engineering technique compared to the developed theoretical algorithm and traditional CAD design are presented.

Implementing automated 3D measurements to quantify reference values and side-to-side differences in the ankle syndesmosis

Detection of syndesmotic ankle instability remains challenging in clinical practice due to the limitations of two-dimensional (2D) measurements. The transition to automated three-dimensional (3D) measurement techniques is on the verge of a breakthrough but normative and side-to-side comparative data are missing. Therefore, our study aim was two-fold: (1) to establish 3D anatomical reference values of the ankle syndesmosis based on automated measurements and (2) to determine to what extent the ankle syndesmosis is symmetric across all 3D measurements. Patients without syndesmotic pathology with a non-weight-bearing CT scan (NWBCT; N = 38; Age = 51.6 ± 17.43 years) and weight-bearing CT scan (WBCT; N = 43; Age = 48.9 ± 14.3 years) were retrospectively included. After training and validation of a neural network to automate the segmentation of 3D ankle models, an iterative closest point registration was performed to superimpose the left on the right ankle. Subsequently, 3D measurements were manually and automatically computed using a custom-made algorithm and side-to-side comparison of these landmarks allowed one to investigate symmetry. Intra-observer analysis showed excellent agreements for all manual measurements (ICC range 0.85–0.99) and good (i.e. < 2.7° for the angles and < 0.5 mm for the distances) accuracy was found between the automated and manual measurements. A mean Dice coefficient of 0.99 was found for the automated segmentation framework. The established mean, standard deviation and range were provided for each 3D measurement. From these data, reference values were derived to differ physiological from pathological syndesmotic alignment. Furthermore, side-to-side symmetry was revealed when comparing left to right measurements (P > 0.05). In clinical practice, our novel algorithm could surmount the current limitations of manual 2D measurements and distinguish patients with a syndesmotic ankle lesion from normal variance.

Quasi-pointwise two-step phase-shifting profilometry with the fringe parameters estimated statistically.

Fringe projection profilometry is a popularly used three-dimensional measurement technique in which phase-measuring algorithms based on two-step phase shifting are usually used because of their best tradeoff between measurement resolution and speed. Most two-step phase-shifting algorithms involve neighboring or other spatial operations, thus having degraded accuracies at edges and discontinuities of the measured object surface. Pointwise two-step algorithms enable overcoming this issue. With them, however, the offsets of the dynamic ranges of the projector and camera are usually improperly overlooked or inaccurately estimated, thus inducing errors in their measurement results. For solving this problem, this paper suggests a quasi-pointwise two-step phase-shifting algorithm for fringe projection profilometry. This algorithm models the captured fringe patterns practically by taking the offsets of the dynamic ranges of the projector and camera into account, and estimates the fringe parameters from the statistics of fringe intensities. As a result, we can calculate fringe phases in a pointwise way from two fringe patterns having a phase difference of π/2 radians. The simulation and experimental results demonstrate that the proposed method has a relatively low level of errors in measuring object surfaces having isolated regions and discontinuities.

Multi-Frequency Fringe Projection Profilometry: Phase Error Suppression Based on Cycle Count Adjustment

Fringe projection profilometry is one of the most widely used three-dimensional measurement techniques at present, in which phase is the key factor for the accuracy of dimensional measurements. Jumping errors may occur due to improper handling of truncation points in phase unwrapping. Meanwhile, projective dual-frequency grating has the shortcomings of a narrow measurement range and coarse projection fringe due to the requirements of an overlapping grid. To address the above problems, this paper puts forward an improved multi-frequency heterodyne phase unwrapping approach. Firstly, the phase principal values of three frequencies are obtained by the standard four-step phase-shifting approach, and two wrapped phases with lower frequencies are obtained through the dual-frequency heterodyne phase unwrapping approach. Then, the decimal part of the fringe order is again calculated using the dual-frequency heterodyne principle, and the actual value of the current decimal part is calculated from the phase principal values of the grating fringe corresponding to the fringe order. Then, a threshold is set according to the error of the phase principal value itself, and the differences between this threshold and the above calculated and theoretical values are compared. Finally, the absolute phase is corrected by adjusting the number of cycles according to the judgment results. Experiments show that the improved approach can achieve a correction rate of more than 96.8% for the jumping errors that occur in phase unwrapping, and it is also highly resistant to noise in the face of different noises. Furthermore, the approach can measure the three-dimensional morphology of objects with different surface morphologies, indicating the certain universality of the approach.

Overturning collapse responses of RC frame-shear wall structures induced by failure of vertical members

In this paper, three 1/5 scaled reinforced concrete (RC) frame-shear wall structural models with single shear wall or cross shear walls on each floor were tested to reveal the mechanism of overturning collapse induced by failure of vertical members. A three-dimensional videogrammetric measurement technique based on high-speed cameras was adopted to acquire spatial locations and status of the moving objects. Overturning collapse was obsessed in all the three structural models after partial vertical members were removed. However, although the structural model with cross shear walls overturned, it did not disintegrate, which indicated that existence of the cross shear walls improved integrity of the structure. Meanwhile, a collapse simulation system was developed based on discrete element method (DEM). Collapse processes of the three structural models, including debris stacking, were predicted and effectiveness of removing the vertical components to simulate dynamic effects in the numerical model was verified. Experimental and numerical results revealed that overturning collapse would be initiated when a sufficient number of vertical components were removed and the flexural bearing capacities of the remaining vertical load bearing members could not resist the impact load of the upper structure for an RC frame-shear wall structure. Parametric analysis indicated that the higher the failure was located, the smaller the damage of the lower remaining structure. Moreover, if the remaining vertical load bearing structural members could not support the upper structure of a high rise building due to insufficient compressive bearing capacities, progressive collapse would take place, and cross shear walls played an important role in resisting collapse for the structure.

Two-Dimensional Post-Traumatic Measurements of Orbital Floor Blowout Fractures Underestimate Defect Sizes Compared to Three-Dimensional Approaches

Orbital floor fractures represent a common fracture type of the midface and are standardly diagnosed clinically as well as radiologically using linear measurement methods. The aim of this study was to evaluate the accuracy of diagnostic measurements of isolated orbital floor fractures based on two-dimensional (2D) and three-dimensional (3D) measurement techniques. A cohort of 177 patients was retrospectively and multi-centrically evaluated after surgical treatment of an orbital floor fracture between 2010 and 2020. In addition to 2D and 3D measurements of the fracture area, further fracture-related parameters were investigated. Calculated fracture areas using the 2D measurement technique revealed an average area of 287.59 mm2, whereas the 3D measurement showed fracture areas with a significantly larger average value of 374.16 mm2 (p < 0.001). On average, the 3D measurements were 1.53-fold larger compared to the 2D measurements. This was observed in 145 patients, whereas only 32 patients showed smaller values in the 3D-based approach. However, the process duration of the 3D measurement took approximately twice as long as the 2D-based procedure. Nonetheless, 3D-based measurement of orbital floor defects provides a more accurate estimation of the fracture area than the 2D-based procedure and can be helpful in determining the indication and planning the surgical procedure.

Coordinate value of the femoral head center estimated using those of the tip of the greater trochanter and lesser trochanter

Several studies have reported estimating the femoral head center (FC) from reference points on the pelvis; however, none have reported estimates obtained from those on the femur. In this cross-sectional study, we investigated the estimated point of FC from the coordinate value of the tip of the greater trochanter (GT) and lesser trochanter (LT) using a formula with a three-dimensional measurement technique. We used data from 92 healthy Japanese subjects without any back or knee symptoms and no abnormalities in the hip, knee, or spine on plain radiographs. In our study, the difference in the anteroposterior direction was larger than that in the other directions. We speculate that the accuracy of defining the tip of the LT is difficult in the anteroposterior direction. Moreover, the correlation coefficients were larger for women. The reason for this was unclear because the variation in the proximal femur may be similar in women. We found that the average difference between the actual and calculated values was approximately 2 mm. We considered that the coordinate value of the FC from the tip of the GT could be estimated more accurately using the regression equation compared to previous methods based on pelvic reference points.

Abrasive slurry jet machining system using polyurethane@silica core-shell particles for internal surfaces of axisymmetric x-ray mirrors.

Abrasive machining has been used for inner surface processing of various hollow components. In this study, we applied an in-air fluid jet as a precision machining method for the inner surface of an axisymmetric x-ray mirror whose inner diameter was less than 10mm. We employed an abrasive with a polyurethane@silica core-shell structure, which has a low density of about 1.2 g/cm3 and a relatively large particle size of about 15 µm. By using this abrasive, a practical removal rate and a smooth machined surface were simultaneously obtained. We performed figure corrections for an axisymmetric mirror and improved the circumferential figure accuracy to a sub-10nm root mean square level. To evaluate the machining performance in the longitudinal direction of the ellipsoidal surface, we also performed periodic figure fabrication on the inner surface of a 114 mm-long nickel ellipsoidal mirror. X-ray ptychography, an optical phase retrieval method, was also employed as a three-dimensional figure measurement technique of the mirror. The wavefield of the x-ray beam focused by the processed ellipsoidal mirror was observed with the ptychographic system at SPring-8, a synchrotron radiation facility. The retrieval calculations for the wavefront error confirmed that a sinusoidal waveform with a period of 12mm was fabricated on the mirror surface. These experimental results suggest that a nanoscale figure fabrication cycle for the inner surface consisting of jet machining and wavefront measurement has been successfully constructed. We expect this technique to be utilized in the fabrication of error-free optical mirrors and various parts having hollow shapes.

Development of a Three-Dimensional Optical Verification Technology without Environmental Pollution for Metal Components with Different Surface Properties.

Nowadays, the optical measuring approach is widely used in the precision machining industry due to high measurement efficiency. In the industry, measuring devices play a crucial role in the field of quality assurance. In practical engineering, the green measurement approach indeed plays an important role in the industry currently. In this study, a state-of-the-art green technique for three-dimensional (3D) optical measurements without environmental pollution is demonstrated, which is an environmentally friendly optical measurement method. This method can perform precise optical measurement without matte coatings. This work dealt with the possibility of measuring four metal components that were not sprayed with anything. The differences in the optical measurement results between with and without matte coatings were investigated and analyzed. It was found that the research result has practical value in the precision machining industry because average size errors of the four measurement objects with different surface properties can be controlled at about 3 µm, 0.1 µm, 0.5 µm, and 9 µm. A technical database with industrial value was established for optical measurements of metal components with different surface properties without matte coatings, which can serve as an alternative to the conventional 3D optical measurement.

Fringe projection profilometry method with high efficiency, precision, and convenience: theoretical analysis and development.

Fringe projector profilometry (FPP) is an important three-dimensional (3D) measurement technique, especially when high precision and speed are required. Thus, theoretical interrogation is critical to provide deep understanding and possible improvement of FPP. By dividing an FPP measurement process into four steps (system calibration, phase measurement, pixel correspondence, and 3D reconstruction), we give theoretical analysis on the entire process except for the extensively studied calibration step. Our study indeed reveals a series of important system properties, to the best of our knowledge, for the first time: (i) in phase measurement, the optimal and worst fringe angles are proven perpendicular and parallel to epipolar line, respectively, and can be considered as system parameters and can be directly made available during traditional calibration, highlighting the significance of the epipolar line; (ii) in correspondence, when two sets of fringes with different fringe orientations are projected, the highest correspondence precision can be achieved with arbitrary orientations as long as these two orientations are perpendicular to each other; (iii) in reconstruction, a higher reconstruction precision is given by the 4-equation methods, while we notice that the 3-equation methods are almost dominatingly used in literature. Based on these theoretical results, we propose a novel FPP measurement method which (i) only projects one set of fringes with optimal fringe angle to explicitly work together with the epipolar line for precise pixel correspondence; (ii) for the first time, the optimal fringe angle is determined directly from the calibration parameters, instead of being measured; (iii) uses 4 equations for precise 3D reconstruction but we can remove one equation which is equivalent to an epipolar line, making it the first algorithm that can use 3-equation solution to achieve 4-equation precision. Our method is efficient (only one set of fringe patterns is required in projection and the speed is doubled in reconstruction), precise (in both pixel correspondence and 3D reconstruction), and convenient (the computable optimal fringe angle and a closed-form 3-equation solution). We also believe that our work is insightful in revealing fundamental FPP properties, provides a more reasonable measurement for practice, and thus is beneficial to further FPP studies.