3D Measurement Method Research Articles

Three-Dimensional Displacement Measurement of Micro-Milling Tool Based on Fiber Array Encoding

The vibration of the micro-milling tool presents a significant chaotic vibration phenomenon, which has a great influence on the tool life and part machining precision, and is one of the basic problems restricting the improvement of machining efficiency and machining accuracy in micro-milling. To overcome the difficulty of the traditional vibration measurement method with the online measurement of micro-milling tool multi-dimensional vibration, a three-dimensional (3D) measurement method of the micro-milling tool is proposed based on multi-fiber array coding, which converts the tool space motion into a decoding process of the optical coding array employing the tool modulating the multi-fiber array encoding. A 6 × 6 optical fiber array was designed, and a 3D motion platform for micro-milling tools was built to verify the characteristics of the optical fiber measurement system. The measurement results show that the measuring accuracy of the system reached 1 µm, and the maximum linear error in x-, y-, and z-direction are 1.5%, 2.58%, and 2.43%, respectively; the tool space motion position measurement results show that the maximum measurement error of the measuring system was 3.4%. The designed system has unique coding characteristics for the tool position in the space of 100 µm3. It provides a new idea and realization means for the online vibration measurement of micro-milling tools.

Differential confocal over-range determination method based on an information theory.

The existing differential confocal axial three-dimensional (3D) measurement method cannot determine whether the surface height of the sample in the field of view is within its effective measurement range. Therefore, in this paper, we propose a differential confocal over-range determination method (IT-ORDM) based on an information theory to determine whether the surface height information of the sample to be examined is within the effective measurement range of the differential confocal axial measurement. First, the IT-ORDM finds the boundary position of the axial effective measurement range by the differential confocal axial light intensity response curve. Then the effective intensity measurement ranges of the pre-focus axial response curve (ARC) and the post-focus ARC are determined by the correspondence between the boundary position and the ARC. Finally, the intersection operation of the pre-focus image of effective measurement and the post-focus image of effective measurement is used to realize the extraction of the effective measurement area of the differential confocal image. The experimental results show that the IT-ORDM can effectively determine and restore the 3D shape of the measured sample surface at the reference plane position in the multi-stage sample experiments.

In-situ 3D contour measurement for laser powder bed fusion based on phase guidance

In-situ layerwise imaging measurement of laser powder bed fusion (LPBF) provides a wealth of forming and defect data which enables monitoring of components quality and powder bed homogeneity. Using high-resolution camera layerwise imaging and image processing algorithms to monitor fusion area and powder bed geometric defects has been studied by many researchers, which successfully monitored the contours of components and evaluated their accuracy. However, research for the methods of in-situ 3D contour measurement or component edge warping identification is rare. In this study, a 3D contour measurement method combining gray intensity and phase difference is proposed, and its accuracy is verified by designed experiments. The results show that the high-precision of the 3D contours can be achieved by the constructed energy minimization function. This method can detect the deviations of common geometric features as well as warpage at LPBF component edges, and provides fundamental data for in-situ quality monitoring tools.

Real-time and accurate monocular 3D sensor using the reference plane calibration and an optimized SGM based on opencl acceleration

Speckle projection profilometry (SPP), as a promising structured light projection technique, can achieve global unambiguous 3D measurement by projecting a single random speckle pattern. In addition, the projected speckle pattern is usually etched into the microstructure of highly integrated Vertical-Cavity Surface-Emitting Laser (VCSEL), which makes the hardware system compact enough to be mounted on mobile devices such as robots. However, since the stereo matching algorithm used in SPP involves high computational overhead, it usually runs in real-time on specially customized hardware platforms such as ASIC/FPGA, rather than general-purpose mobile platforms. In this paper, we propose a real-time and accurate 3D measurement method using a monocular 3D sensor based on the infrared speckle projection. Similar to Kinect v1, our sensor mainly consists of an IR dot projector and one IR camera for projecting and capturing speckle images synchronously. Low-cost and high-quality speckle projection is achieved by customizing the projection pattern of VCSEL and using the beam copy function of Diffractive Optical Elements (DOE). Based on the 3D imaging principle of monocular 3D sensors, a reference plane calibration method is proposed to obtain a high-quality reference speckle image for improving the monocular matching accuracy. Then, benefited from the local memory mechanism and multiple operating synchronizations on the OpenCL environment, an optimized semi-global matching (SGM) algorithm using GPU is presented to achieve efficient and accurate depth reconstruction dynamically. Within the measurement range of 0.8m (length) ×0.5m (width) ×1m (depth), the proposed method can achieve real-time and single-shot 3D imaging with an accuracy of 1.277 mm at 75 FPS on GTX 1060 and 15 FPS on ARM Mail G52(mobile platform).

Three-dimensional structural displacement measurement using monocular vision and deep learning based pose estimation

Computer vision-based displacement measurement methods have received increasing attention for the structural health monitoring of buildings and infrastructures owing to their advantages over traditional contact sensors. Meanwhile, surveillance cameras widely equipped in urban areas can record a large number of images and videos of buildings and infrastructure, which have the potential to support structural analysis in structural health monitoring or engineering investigations. The three-dimensional (3D) displacement of structures is important for structural analysis. It is challenging for the existing vision-based measurement methods to obtain all the 3D displacement components because they require either multi-view camera systems or additional specially designed targets, which makes it difficult to meet the requirements of measurement applications based on urban surveillance cameras. Therefore, this study proposes a 3D structural displacement measurement method using monocular vision and deep learning based pose estimation. The method uses virtual rendering to synthesize the training set based on the 3D models of the target objects, then trains the deep learning model DPOD (Dense Pose Object Detector) to estimate the poses of the target object, and finally measures the 3D translation of the structures based on the original and destination poses or the original pose and keypoint matching. The effectiveness of the proposed method was validated through static and dynamic experiments. The results showed that the method can meet the needs of obtaining 3D structural displacement and has good accuracy in identifying the principal frequencies of the dynamic responses. The proposed method can support the 3D displacement measurements of buildings and infrastructure based on urban surveillance cameras.

A new method for high dynamic range 3D measurement combining adaptive fringe projection and original-inverse fringe projection

For fringe projection profilometry (FPP), high reflections on metal, plastic, and ceramic surfaces cause intensity saturation, resulting in three dimensional (3D) measurement errors. The measurement efficiency using the multiple exposure method (MEM) is low and the exposure time is difficult to quantify. The original and inverse fringe projection method (OIFPM) suffers from saturation of the opposite fringes on highly reflective surfaces. The adaptive fringe projection method (AFPM) is still limited by image dynamic range and pixel mapping accuracy. To this end, this paper proposes a new scheme combining OIFPM and AFPM, called the original and inverse adaptive fringe projection method (OIAFPM). Firstly, an adaptive intensity template in the camera coordinate system is generated. Secondly, a pixel mapping between the camera and projector images is established. Thirdly, original and inverse adaptive fringes are generated and projected. Finally, 72 wrapped phase calculation equations are given in detail. Experiments confirm that the 3D measurement employing the proposed OIAFPM is much better than that employing AFPM and OIFPM. Although the 3D measurement employing MEM is similar to that employing OIAFPM, the measurement efficiency employing OIAFPM is much higher than that employing MEM.

Research on highly dynamic 3D measurement method based on RGB color fringe projection

Metal parts with highly dynamic areas often appear in industrial production measurements. However, if the traditional fringe projection technique is used to project fringe onto the surface of these metal parts, the light energy will be excessively concentrated and the image will be saturated, resulting thus in the loss of fringe information. To effectively address the high reflectivity problem of the object under test in fringe projection, background normalized Fourier transform contouring was combined with adaptive fringe projection in this work and a new method for performing highly dynamic 3D measurements was proposed. To reduce the number of the acquired images by the camera, a monochromatic fringe of different frequencies was put into the RGB channel to make color composite fringe, and then a color camera was used to acquire the deformed color composite fringe map. The images acquired by the color camera were then separated into three channels to obtain three deformed stripe maps. The crosstalk was also removed from these three images, and the 3D shape of the object was reconstructed by carrying out Fourier transform contouring with background normalization. From our experiments, it was demonstrated that the root mean square error of the proposed method can reach 0.191 mm, whereas, unlike the traditional methods, the developed method requires four images.

Three-dimensional shape measurement method based on composite cyclic phase coding.

Phase coding is widely used in 3D measurement due to its good anti-interference and robustness. However, the measurement accuracy is affected by the limitation of the number of codewords. To solve this problem, we propose a 3D shape measurement method based on composite cyclic phase coding. The traditional phase coding is quantized cyclic without adding extra patterns, further adopting composite coding, using the composite cyclic phase coding grayscale values to distinguish the same cyclic codewords, and finally integrating them into a new fringe order sequentially for phase unwrapping to achieve effective expansion of codewords. The related experimental results show that the proposed method stably achieves high accuracy 3D reconstruction, which overcomes the misjudgment of codewords caused by traditional phase coding under high-frequency fringes due to system nonlinearity and noise. Meanwhile, compared with the improved phase coding method of temporal domain combined with spatial domain information, such as the method of quantized phase coding and connected region labeling, it can effectively avoid the phenomenon of error propagation, with high robustness and low algorithm complexity.

Orthogonal dual-channel single-camera spectral imaging for online measurement of three-dimensional space–time evolution of temperature field in laser melt pool

Current temperature measurement technology in laser manufacturing cannot obtain the internal three-dimensional (3D) temperature distribution of the melt pool. Necessary information for laser-manufacturing process optimization is lacking, including the melt pool depth and depth-to-width ratio. We propose a method for 3D temperature measurement based on orthogonal dual-channel single-camera spectral imaging. The 3D temperature field distribution of the melt pool can be obtained by collecting projected radiation data from two perpendicular angles. Use of a single monochrome camera for spectral imaging at three wavelengths ensures excellent spatial and temporal consistency during measurements. To verify the feasibility of the method, we measured the 3D temperature field in a melt pool of 304 stainless steel irradiated by a Gaussian laser beam (continuous laser, 500 W) with different irradiation times. The results indicate that the temperature field exhibits an approximately axisymmetric distribution on each cross-section at different depths. The temperature is highest in the center and gradually decreases around it. As the depth increases, the high-temperature area (>1730 K) gradually becomes smaller, and the temperature of each cross-section decreases. The maximum temperature, depth, width, and depth-to-width ratio of the melt pool at different times were obtained from the measured 3D temperature distributions. With an irradiation time of 0–80 s, the maximum temperature of the melt pool exhibited three stages: rapid increase (20–2230 K), slow increase (2230–2280 K), and stabilization. The growth of the width and depth of the melt pool indicated a similar process, increasing rapidly at first and gradually slowing. The depth-to-width ratio decreased rapidly at first and gradually stabilized. The proposed method for 3D temperature measurement has potential use in laser manufacturing for process control and quality improvement.

A Continuous Motion Shape-from-Focus Method for Geometry Measurement during 3D Printing.

In 3D printing, as in other manufacturing processes, there is a push for zero-defect manufacturing, mainly to avoid waste. To evaluate the quality of the printed parts during the printing process, an accurate 3D measurement method is required. By scanning the part during the buildup, potential nonconformities to tolerances can be detected early on and the printing process could be adjusted to avoid scrapping the part. Out of many, shape-from-focus, is an accurate method for recovering 3D shapes from objects. However, the state-of-the-art implementation of the method requires the object to be stationary during a measurement. This does not reconcile with the nature of 3D printing, where continuous motion is required for the manufacturing process. This research presents a novel methodology that allows shape-from-focus to be used in a continuous scanning motion, thus making it possible to apply it to the 3D manufacturing process. By controlling the camera trigger and a tunable lens with synchronous signals, a stack of images can be created while the camera or the object is in motion. These images can be re-aligned and then used to create a 3D depth image. The impact on the quality of the 3D measurement was tested by analytically comparing the quality of a scan using the traditional stationary method and of the proposed method to a known reference. The results demonstrate a 1.22% degradation in the measurement error.

Quantification of prostate tumour diameter and volume from MR images using 3D ellipsoid model and its impact on PI-RADS v2.1 assessment

Maximum diameter and volume of the tumour provide important clinical information and are decision-making parameters for patients suspected with prostate cancer (PCa). The objectives of this study were to develop an automated method for 3D tumour measurement and compare it with the radiologist’s manual assessment, as well as to investigate the impact of 3D tumour measurement on Prostate Imaging-Reporting and Data System version-2.1 (PI-RADS v2.1) scoring of prostate cancer. Tumour maximum diameter and volume were calculated using automated ellipsoid-fit method. For all PI-RADS scores, mean ± standard deviation range of tumour maximum diameter and volume measured using ellipsoid-fit method were 1.36 ± 0.28 to 1.97 ± 0.67 cm and 0.49 ± 0.31 to 1.05 ± 0.78 cc and manual assessment were in range of 0.73 ± 0.12 to 1.14 ± 0.25 cm and 0.36 ± 0.21 to 0.93 ± 0.39 cc, respectively. Ellipsoid-fit method showed significantly (p < 0.05) higher values for maximum diameter and volume than manual assessment. 3D measurement of tumour using ellipsoid-fit method was found to have higher maximum diameter and volume values (in 40–61% patients) compared to conventional assessment by radiologist, which may have an impact on PI-RADS v2.1 scoring system.

3D reconstruction method based on the optimal projection intensity of a polarization system.

The measurement of shiny objects is a major challenge for structured light 3D measurement. Polarization systems can be used to measure shiny objects. However, the polarizer may attenuate the light intensity of the captured image, reducing the SNR of the image, and the measurement accuracy will be affected. To improve the measurement accuracy and efficiency, this paper proposes a 3D measurement method based on polarization optimal projection intensity. By establishing the camera response function under the polarization system, the desired optimal projection intensity can be directly estimated and used to compensate for the image light intensity attenuated by the additional polarizer. This method does not require rotating polarizers and multiple exposure times. In addition, the optimal fringe images are obtained by applying image fusion algorithms. The experimental results show that the method improves pixels in the image that are too dark, while significantly reducing the saturated pixels on the shiny surface. This method can effectively improve the image contrast, get better fringe images, extract more effective information, and reconstruct a more complete 3D point cloud.

Reconceptualization of Trochlear Dysplasia in Patients With Recurrent Patellar Dislocation Using 3-Dimensional Models.

Common classification schemes, measurements, and surgical planning for trochlear dysplasia are predicated on 2-dimensional imaging views. To investigate patellofemoral joint osseous anatomy using 3-dimensional (3D) printed models to describe osseous anatomic trochlear variations in patients with recurrent patellar dislocation. Cross-sectional study; Level of evidence, 3. Computed tomography scans were obtained from 20 patients with recurrent patellar dislocation and 10 healthy control knees, and 3D prints generated from these computed tomography scans were studied with respect to mediolateral positioning of the proximal trochlear groove and groove obliquity as well as changes in the appearance, height, and orientation of the medial and lateral trochlear ridges. Each trochlea was centered with respect to a vertical line perpendicular to the distal femoral condyles and through the central intercondylar notch roof, with the 3D models resting on their posterior femoral condyles. A novel 3D measurement method was devised to assess groove obliquity, termed the entry point-transition point (EP-TP) angle. The EP was defined as the midpoint of the flattened region of the proximal trochlea where the lateral and medial ridges of the proximal trochlea meet, and the TP was the point along the trochlear groove at which the groove shape changes from an oblique orientation proximally to one more vertical distally. Measurements were obtained by 3 reviewers, and reliability analyses were performed. With the dysplastic knees arranged according to flattening of the trochleas, increased obliquity of the trochlear grooves was observed, as reflected by increased EP-TP angles as well as more lateral patellar EPs into the proximal trochleas of these recurrent patellar dislocation knees when compared with the control knees. The degree of trochlear dysplasia (according to the Dejour classification and trochlear flatness in the frontal and axial planes) was associated with diminished prominence of the lateral trochlear convexity, increasingly lateralized proximal trochlear EPs, increased trochlear groove obliquity, lateral trochlear curvature, and progressive medial ridge deformity. The 3D reproductions enabled unique conceptualization of trochlear deformity associated with recurrent patellar dislocation.

Littrow 3D measurement based on 2D grating dual-channel equal-optical path interference.

We propose a 3D measurement method based on 2D grating dual-channel and Littrow equal-optical path incidence to detect the 3D displacement of a 2D grating in the X-, Y-, and Z-directions. The 2D grating is combined with the Littrow incidence method and a turning element to cause the Littrow diffracted light with frequency f1 to interfere with the reference light at frequency f2, and the displacement data in the X-, Y-, and Z-directions are obtained using the separation-dual-channel phase decoupling algorithm. A corresponding test experimental platform is constructed, and linear error evaluation and step error evaluation experiments are performed to determine the displacements in the X-, Y-, and Z-directions. The results obtained show that all linearity errors are within ±60 nm in the 10 mm measurement ranges in the X-, Y-, and Z-directions, and the test resolution is within ±5 nm. The proposed method can thus realize nanoscale synchronous measurement of X-, Y-, and Z-direction 3D displacements.

3D assessment of initial fracture displacement of tibial plateau fractures is predictive for risk on conversion to total knee arthroplasty at long-term follow-up

PurposeCurrently used classification systems and measurement methods are insufficient to assess fracture displacement. In this study, a novel 3D measure for fracture displacement is introduced and associated with risk on conversion to total knee arthroplasty (TKA).MethodsA multicenter cross-sectional study was performed including 997 patients treated for a tibial plateau fracture between 2003 and 2018. All patients were contacted for follow-up and 534 (54%) responded. For all patients, the 3D gap area was determined in order to quantify the degree of initial fracture displacement. A cut-off value was determined using ROC curves. Multivariate analysis was performed to assess the association of 3D gap area with conversion to TKA. Subgroups with increasing levels of 3D gap area were identified, and Kaplan–Meier survival curves were plotted to assess survivorship of the knee free from conversion to TKA.ResultsA total of 58 (11%) patients underwent conversation to TKA. An initial 3D gap area ≥ 550 mm2 was independently associated with conversion to TKA (HR 8.4; p = 0.001). Four prognostic groups with different ranges of the 3D gap area were identified: excellent (0–150 mm2), good (151–550 mm2), moderate (551–1000 mm2), and poor (> 1000 mm2). Native knee survival at 10-years follow-up was 96%, 95%, 76%, and 59%, respectively, in the excellent, good, moderate, and poor group.ConclusionA novel 3D measurement method was developed to quantify initial fracture displacement of tibial plateau fractures. 3D fracture assessment adds to current classification methods, identifies patients at risk for conversion to TKA at follow-up, and could be used for patient counselling about prognosis.Level of evidencePrognostic Level III.

Efficient 3D measurement of a HDR surface basedon adaptive fringe projection.

3D measurement methods of a high-dynamic-range (HDR) surface based on adaptive fringe projection have aroused extensive research interest. They tend to pixel-wise adjust the fringe projection intensity to ensure full-field phase quality in light or dark regions, which has two problems: (1)traditional image intensity-based temporal phase unwrapping (TPU) is susceptible to noise in dark regions, and (2)it is time-consuming to project orthogonal fringe patterns for coordinate mapping and 3D reconstruction. Aiming to address these issues, we present an efficient adaptive fringe projection method where misaligned Gray code patterns are adopted to remove the phase error induced by low-frequency fringe patterns. Compared with traditional image intensity-based TPU, misaligned Gray-code-based TPU provides a better noise-suppression effect in dark regions, as Gray codes are generally better preserved than image intensity. Moreover, the images captured in the coordinate mapping process are shared for optimal projection intensity calculation and 3D reconstruction to reduce the number of total projection patterns, thus improving measurement efficiency. Extensive contrast experiments are conducted to demonstrate that the proposed method retrieves the 3D shapes of micro-scale HDR surfaces with high accuracy and a minimum number of projection patterns on the premise of high measurement integrity.

A 3D measurement method of bubbles based on edge gradient segmentation of light field images

Based on the light field imaging technology, a three-dimensional(3D) measurement method of bubbles through the use of edge gradient segmentation (TMBEGS) is proposed in this paper. From the characteristic that the bubble edge image has great gray gradient, the coordinates of the bubble edge pixels are determined. The depths of the edge pixels are further derived by evaluating the sharpness of the edge pixels in the refocused light field images. On this basis, the depth coordinate of the bubble is calculated by averaging the depths of all edge pixels, and the 3D measurement of the bubble is then achieved by combining the centroid coordinate and equivalent diameter of the bubble. Finally, experiments are carried out to evaluate TMBEGS on a calibration setup and a bubbling bed experimental device. Results indicated that the relative errors of the bubble diameter and depth by TMBEGS are less than 1.18 % and 5.93 %, which are better than 2.99 % and 17.51 % by the existing method, respectively. On the bubbling bed experimental device, the equivalent diameter of bubbles is increased by 5.69 % compared with the existing method, and the standard deviation of the bubble depth is less than 1.78 mm, which is 21.3 % lower than the existing method. With the increase of the bubble equivalent diameter, the bubble surface deformation intensifies under the effects of the bubble surface tension, viscous force, and inertia force, which affects the imaging quality of the bubble, and reduces the measurement accuracy of the bubble edge and depth. These results illustrated that TMBEGS has high measurement accuracy of the bubbles and is capable of charactering the bubbles in the gas–liquid two-phase flow system.

Research on the layout of primary control network and new measurement method for the HIAF survey and alignment

HIAF (High Intensity heavy ion Accelerator Facility) is one of the major national science and technology infrastructure projects in the “12th Five-Year Plan” undertaken by the Institute of Modern Physics, CAS. The primary control network, as the basic framework of the local coordinate system control of the particle accelerator, is the basis for calculating the coordinates in the process of accelerator construction and implementation, and plays a very important role in the survey and alignment during the construction period and the maintenance and monitoring during the operation period. Based on the multi-dissimilar design structure of HIAF and the unique geological conditions of the construction area, a new high-density layout method of the primary control network and a high-precision 3D(three-dimensional) measurement method were studied, and were successfully applied to the survey and alignment of HIAF. Inside and outside the accelerator tunnel, a high-density 3D primary control network that can form a full envelope for the accelerator beam is respectively laid out. All primary control networks are embedded in the bedrock layer with stainless steel reference inner cylinder and outer protective cylinder, and special waterproof filling layer is set up. All primary control network points in the accelerator tunnel are equipped with measuring intervisible holes and measurement platforms that can directly perform 3D measurements on the ground. By setting up the laser tracker on the horizontal attitude of the measurement platform, the 3D coordinates of the primary control network points inside and outside the accelerator tunnel can be measured directly and with high precision, and the simultaneous adjustment of the measurement data can be completed. The HIAF primary control network layout and measurement method proposed in this paper overcomes the problems of heavy pile foundation, poor crack resistance and poor water seepage resistance of the primary control network laid by the traditional method and solves the problem that the traditional primary control network must separate the plane network and the elevation network for independent measurement. The traditional method of tunnel point and forced centering measurement is avoided. By using a laser tracker to directly measure the 3D coordinates of the primary control network points inside and outside the tunnel, the measurement efficiency and measurement accuracy of the primary control network are improved, and the reliability of primary control network measurements is increased. The feasibility and correctness of the HIAF primary control network layout and measurement method are verified by comparing the actual multi-system measurement results in the field. This method has a certain reference value for the layout of the primary control network of the same type of accelerator.

A new quantitative 3D gap area measurement of fracture displacement of intra-articular distal radius fractures: Reliability and clinical applicability.

IntroductionGap and step-off measurements are generally used in the surgical decision-making process of distal radius fractures. Unfortunately, there is no consensus on treatment choice as these measurements are prone to inter- and intraobserver variability. In this study, we aim to introduce a new 3D fracture quantification method and compare it to conventional fracture analysis.MethodsForty patients with a minimally displaced intra-articular distal radius fracture that was treated nonoperatively between 2008–2015 were included. 2D-CT images were reassessed by three orthopedic trauma surgeons who performed gap and step-off measurements. Subsequently, 3D models were created and a 3D measurement method for fracture displacement was developed. For each fracture, the ‘3D gap area’ (3D surface between all fracture fragments) was determined by three observers. Interobserver agreements were calculated for all measurements, and the intraobserver agreement was calculated for the new 3D measurement. All patients completed two questionnaires in order to link our measurements to functional outcome.ResultsThe interobserver agreement of the 2D measurements was fair (ICC = 0.54) for the gap and poor (ICC = 0.21) for the step-off. The median gap was 2.8 (IQR: 1.9–3.5) mm and step-off was 0.9 (IQR: 0.0–1.6) mm. Interobserver agreement on 3D gap area measurements was excellent (ICC = 0.81), with a median difference between measurements of 6.0 (IQR: 2.0–19.0) mm2, which indicates reliable assessment of 3D fracture displacement. Intraobserver agreement was also excellent (ICC = 0.98), with a median difference of 4.0 (IQR: 1.5–5.5) mm2. No significant differences in clinical outcome were found between the above and below 2mm displacement groups. The score of the DASH was 3.4 (IQR: 0.4–8.8) versus 4.2 (IQR: 0.0–11.6) respectively. Results from the PRWE questionnaire shows a similar result of 3.5 (IQR: 0.0–12.6) versus 5.0 (IQR: 0.0–25.5).Conclusion3D gap area is a more objective measurement method compared to the conventional gap and step-off measurements to quantify the level of fracture displacement of distal radius fractures. 3D fracture assessment can be used in addition to the currently used classification systems of distal radius fractures.

Three-dimensional measurement for specular reflection surface based on deep learning and phase measuring profilometry

ObjectivePhase measuring profilometry (PMP) is a non-contact 3D measurement method. However，it is still a very challenging task when it is applied to an object with a specular reflection surface. In this paper, a 3D measurement method for specular reflection surface based on a deep learning framework is proposed to reduce the measurement error caused by highlights. MethodsFirstly, a dual-channel U-Net network (DC-UNet) is used to identify the highlight areas in the fringe image. Secondly, the dilated residual networks (DRN) combined with the features of the neighborhood of the highlight pixels are used to correct the highlight pixels, and the predicted fringe image without highlight can be obtained. Thirdly, the predicted fringe image is blended with the original image, regarded as the final result of the highlight removal. Fourthly, phase unwrapping is implemented using the fringe image of highlight removal, and the 3D coordinates values can be obtained by combining the calibrated parameters with the phase values unwrapped. ResultsSimulated results show that the absolute maximum deviation, absolute mean error and standard deviation of reconstructed 3D height coordinates are reduced by 98.27 %, 68.70 %, and 91.11 %, respectively. The real experiment results show that the maximum error of the absolute phase is reduced by more than 87.00 %, and the mean error of the absolute phase is reduced by more than 92.72 %. Finally, more than 99.14 % of the pixels with intensity saturated caused by highlights can be corrected by the proposed method.