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A fringe projection system, in special application scenarios, is used for three-dimensional (3D) shape measurement through a transparent medium. The light refraction caused by the medium gives rise to erroneous 3D data in conventional fringe projection methods. In this work, we propose ray-tracing-based 3D profilometry using fringe projection. The method uses phase information for seeking the homologous points between camera images and projector images pixel by pixel. Equations of light rays emitted from each point pair are identified with the law of flat refraction. A midpoint of skew lines common perpendicular algorithm is developed for calculating the intersections of these equations, which are 3D shape data without refraction error. For validation, a fringe projection system through a transparent glass was set up and applied for 3D shape measurements. The results verify the effectiveness and accuracy of the proposed ray-tracing-based 3D profilometry. [ABSTRACT FROM AUTHOR]

Cold spray is a material deposition technology with a high deposition rate and attractive material properties that has great interest for additive manufacturing (AM). Successfully cold spraying free-form parts that are close to their intended shape, however, requires knowing the fundamental shape of the sprayed track, so that a spray path can be planned that builds up a part from a progressively overlaid sequence of tracks. Several studies have measured track shape using ex situ or quasi-in situ approaches, but an in situ measurement approach has, to the authors' knowledge, not yet been reported. Furthermore, most studies characterize the track cross section as a symmetric Gaussian probability density function (PDF) with fixed shape parameters. The present study implements a novel in situ track shape measurement technique using a custom-built nozzle-tracking laser profilometry system. The shape of the track is recorded throughout the duration of a spray, allowing a comprehensive investigation of how the track shape evolves as the deposit is built up. A skewed track shape is observed—likely due to the side-injection design of the applicator used—and a skewed Gaussian PDF—a more generalized version of the standard Gaussian PDF—is fit to the track profile. The skewed Gaussian fit parameters are studied across two principal nozzle path parameters: nozzle traverse speed and step size. Empirical relationships between the fit parameters and the nozzle path parameters are derived, and a physics-based inverse relationship between nozzle speed and powder mass deposition rate is obtained. One of the fit parameters is shown to be an effective means of monitoring deposition efficiency during spraying. Overall, the approach presents a promising means of measuring track shape, in situ, as well as modeling it using a more general shape function. [ABSTRACT FROM AUTHOR]

Background: Stereo-DIC is a widely used optical measurement technique that provides a dense full-field 3D measurement of the shape, displacement, and strain of a solid sample. When compared with 2D-DIC, Stereo-DIC provides greater flexibility and expands its use beyond flat, planar specimens. Furthermore, the widespread availability of commercial systems has led to the adoption of the technique throughout industry, academia, and government research labs. Objective: Even though some research has been done to understand the effects of different experimental and stereo-DIC parameters, no reference is available to benchmark and compare the performance of current stereo-DIC algorithms to each other. Methods: This paper provides the description and analysis of a carefully controlled 3D experiment and associated images used to compare the results from five subset based DIC software packages. Both the images and analysis codes used in this paper to compare the results are described here and are available for download and use for continued research. Results: We show that over a very large range of motion, the 3D errors are very small, less than 80 μ m over a travel of ±20 mm out-of-plane and ±20 mm in-plane. While all codes performed similarly, there are important differences noted in the paper. Conclusion: The image sets and results comparison software are hosted by the International DIC Society (www.iDICs.org) and are freely available for download and analysis for comparison with results in this paper. Furthermore, it is hoped that this set of images can be used for future research in improving stereo-DIC by future authors. [ABSTRACT FROM AUTHOR]

This paper proposes a 3D shape measurement method based on Res-Attention-Unet for deep learning, which effectively integrates single-frame fringe phase extraction and temporal phase unwrapping. The Res-Attention-Unet, trained with a large amount of data, is shown to be able to extract phase information directly from deformed fringe patterns with large frequency differences and to achieve high-precision and unambiguous 3D measurement using hierarchical phase unwrapping. We experimentally demonstrate that the method requires only three deformed fringe patterns with different frequencies to achieve accurate and 3D measurement, and Res-Attention-Unet has an absolute advantage over the traditional single-frame fringe phase extraction algorithm in terms of the phase extraction accuracy of low-frequency fringe patterns. Since only three fringe patterns need to be projected, this method is expected to be applied to project single-frame color fringe for dynamic 3D measurement. [ABSTRACT FROM AUTHOR]

It is imperative to achieve the co-phase state for large segmented mirrors of telescopes. This paper proposes a novel method for quantifying the co-phase errors of the segmented mirrors, as well as to detect any residual errors by analyzing the surface shape of segmented mirrors using conformal mapping after the correction of the co-phase errors, aiming to achieve a more precise co-phase state. This method applies a dual-wavelength phase-shifting interferometry based on optical vortex to measure the co-phase errors (i.e., tip, tilt, and piston), and measures the surface shape of segmented mirrors based on conformal mapping phase-shifting interferometry to identify which kind of co-phase errors still exist there, and then adjust the segmented mirrors to achieve a more precise co-phase state. The functional relationships between piston error or tip/tilt error and phase distribution in the image plane are derived, and the mathematical tool of conformal mapping is used for surface shape demodulation. The experiment results indicate that the resolution of the piston error measurements is 1.878 nm, and the resolution of the tip/tilt error measurements is 0.760″. Furthermore, the surface shape measurement after adjustment based on conformal mapping phase-shifting interferometry is 7.503 nm (RMS). [ABSTRACT FROM AUTHOR]

Full-field three-dimensional (3D) measurement technology based on phase information has become an indispensable part of geometric dimension measurement in modern scientific research and engineering applications. This field has been developing and evolving for the study of highly reflective phenomena, diffuse reflections, and specular surfaces, and many novel methods have emerged to increase the speed of measurements, enhance data accuracy, and broaden the robustness of the system. Herein, we will discuss the latest research progress in full-field 3D shape measurement based on phase information systematically and comprehensively. First, the fundamentals of 3D shape measurement based on phase information are introduced, namely, phase-shifting and transform-based methods. Second, recent technological innovations are highlighted, including increases in measurement speed and automation and improvements in robustness in complex environments. In particular, the challenges faced by these technological advances in solving highly dynamic, composite surface measurement problems are presented, i.e., with multiexposure techniques proposed for high dynamics that extend the dynamic range of the camera to reduce the effects of overexposure but increase the cost of time and have high hardware requirements, fringe adaptive techniques that overcome light variations but are computationally complex, and multipolarized camera techniques that reduce the effects of light variations but are sensitive to the light source. Third, the phase-shifting method combined with coding is proposed to improve the measurement speed, but the accuracy is slightly reduced. Deep learning techniques are proposed to cope with measurements in complex environments, but the dataset computation process is cumbersome. Finally, future research directions are suggested, and the challenges are presented. Overall, this work provides a reference for researchers and engineers. Highlights: This paper reviews advancements in technology aimed at the high precision and high speed of measurements, ensuring more efficient and reliable full-field 3D shape measurements. The challenges related to the advancement of error compensation for phase calculations are outlined and discussed in various techniques with their advantages and trade-offs. The examination of future research directions and challenges in the field of full-field 3D measurements based on phase information culminates by providing insightful perspectives. [ABSTRACT FROM AUTHOR]

Aircraft icing can cause severe aerodynamic and flight mechanical effects, thus threatening aircraft flight safety. Understanding of aircraft icing, e.g., geometry shape of the ice accretion, is significant for its aerodynamic analysis, control methodologies, and continued design. In this study, a laser sheet scanning approach is developed to achieve the time-resolved geometry shape measurements of the ice accretion. By using the tridimensional calibration board consisted of two special checkerboard plates, all laser plane coefficients during laser sheet scanning could be obtained in advance. Then, based on the two-stage laser line extraction scheme that combined the Steger method with gradient centroid calculation, accurate positioning of the laser lines projected on the ice accretion surface was realized. The proposed approach is demonstrated in the large-scale icing wind tunnel tests of an airfoil model, conducted at the 3 m × 2 m Icing Wind Tunnel of China Aerodynamics Research and Development Center. Temporal evolution of the rime, mixed, and clear ice accretion shapes on the leading edge of the airfoil model was measured throughout the tests, respectively. The measurement at the end of ice accretion was compared with the results by a commercial 3D laser scanner, which showed highly consistent. [ABSTRACT FROM AUTHOR]

Particle shape variability is a key to understanding the rich behavior of granular materials. Polyhedra are among the most common particle shapes due to their ubiquitous origins in nature such as rock fragmentation and mineral crystallisation. Because of their faceted shape, polyhedral particles tend to assemble in jammed structures in which face-face and face-edge contacts between particles control the packing-level properties. In this paper, we use tri-periodic particle dynamics simulations to derive for the first time a generic analytical expression of the elastic moduli of polyhedral and spherical particle packings subjected to triaxial compression as a function of two contact network variables: (1) a "constraint number" that accounts for the face-face and edge-face contacts between polyhedra and is reduced to the coordination number in the case of spherical particles, and (2) the contact orientation anisotropy induced by compression. This expression accurately predicts the simulated evolution of elastic moduli during compression, revealing thereby the origins of the higher elastic moduli of polyhedral particle packings. We show that particle shape affects the elastic moduli through its impact on the contact network and the level of nonaffine particle displacements is the same for the simulated shapes. Its nearly constant value during compression underlies the constant values of our model parameters. By connecting the elastic moduli to the contact network through parameters that depend on particle shape, our model makes it possible to extract both the connectivity and anisotropy of granular materials from the knowledge of particle shape and measurements of elastic moduli. [ABSTRACT FROM AUTHOR]

We update the full set of B ¯ s → K form factors using light-cone sum rules with an on-shell kaon. Our approach determines the relevant sum rule parameters — the duality thresholds — from a Bayesian fit for the first time. Using a modified version of the Boyd-Grinstein-Lebed parametrisation, we combine our sum rule results at low momentum transfer q2 with more precise lattice QCD results at large q2. We obtain a consistent description of the form factors in the full q2 range. Applying these results to a recent LHCb measurement of branching ratios for the decays B s 0 → {K−, D s − }μ+νμ, we determine the ratio of Cabibbo-Kobayashi-Maskawa elements V ub V cb q 2 < 7 GeV 2 = 0.0681 ± 0.0040 and V ub V cb q 2 > 7 GeV 2 = 0.0801 ± 0.0047 , which are mutually compatible at the 1.9σ level. We further comment on the sensitivity to Beyond the Standard Model effects through measurements of the shape of B s 0 → K−μ+νμ decays, in light of recent limits on such effects from other exclusive b → uℓν processes. [ABSTRACT FROM AUTHOR]

Objective: This study presents an extended evaluation of a numerical approach to simulate artifacts of metallic implants in an MR environment. Methods: The numerical approach is validated by comparing the artifact shape of the simulations and measurements of two metallic orthopedic implants at three different field strengths (1.5 T, 3 T, and 7 T). Furthermore, this study presents three additional use cases of the numerical simulation. The first one shows how numerical simulations can improve the artifact size evaluation according to ASTM F2119. The second use case quantifies the influence of different imaging parameters (TE and bandwidth) on the artifact size. Finally, the third use case shows the potential of performing human model artifact simulations. Results: The numerical simulation approach shows a dice similarity coefficient of 0.74 between simulated and measured artifact sizes of metallic implants. The alternative artifact size calculation method presented in this study shows that the artifact size of the ASTM-based method is up to 50% smaller for complex shaped implants compared to the numerical-based approach. Conclusion: In conclusion, the numerical approach could be used in the future to extend MR safety testing according to a revision of the ASTM F2119 standard and for design optimization during the development process of implants. [ABSTRACT FROM AUTHOR]

Pulmonary fissure segmentation in computed tomography (CT) images can be treated as important ancillary information in the diagnosis and treatment of pulmonary diseases, yet it poses a nontrivial uncertainty for the segmentation task due to complex structures such as indistinguishable pulmonary vessels, blurring pulmonary fissures and unpredictable pathological deformation. To address these challenges, a useful approach based on an oriented derivative of stick (ODoS) filter and shape features is presented for pulmonary fissure segmentation. Here, we adopt an ODoS filter by fusing its orientation and magnitude information to highlight structural features for fissure enhancement, which can effectively distinguish between pulmonary fissures and undesirable clutter. Motivated by the fact that pulmonary fissures appear as linear structures in 2D space and planar structures in 3D space in the orientation field, an orientation curvature criterion and an orientation partition scheme are fused to separate fissure patches and other structures in different orientation partitions, which is expected to achieve more complete fissure detection and suppress other structures. Considering the shape difference between pulmonary fissures and tubular structures in the magnitude field, a shape measurement approach and a 3D skeletonization model are combined to remove clutter for pulmonary fissure segmentation. When applying our scheme to 55 chest CT scans acquired from publicly available LOLA11 datasets, the median F1-score, false discovery rate (FDR), and false negative rate (FNR) were 0.90, 0.11, and 0.10, respectively, which indicates that our scheme has satisfactory pulmonary fissure segmentation performance. [ABSTRACT FROM AUTHOR]

In the absence of gravity, surface tension dominates over the behavior of liquids. While this often poses a challenge in adapting Earth-based technologies to space, it can also provide an opportunity for novel technologies that utilize its advantages. In particular, surface tension drives a liquid body to a constant-mean-curvature shape with extremely smooth surfaces, properties which are highly beneficial for optical components. We here present the design, implementation and analysis of parabolic flight experiments demonstrating the creation and in-situ measurement of optical lenses made entirely by shaping liquids in microgravity. We provide details of the two experimental systems designed to inject the precise amount of liquid within the short microgravity timeframe provided in a parabolic flight, while also measuring the resulting lens' characteristics in real-time using both resolution target-imaging and Shack-Hartmann wavefront sensing. We successfully created more than 20 liquid lenses during the flights. We also present video recordings of the process, from the lenses' creation during microgravity and up until their collapse upon return to gravity. The work thus demonstrates the feasibility of creating and utilizing liquid-based optics in space. [ABSTRACT FROM AUTHOR]

The advance of minimally invasive interventional surgeries has accelerated the iterative upgrading of continuum surgical robots. High compatibility with robotic applications and high precision are key features of sensors for robot navigation. In this paper, a spun multi-core fibre (SMCF) 3D shape sensor for continuum surgical robots is proposed. The sensor is fabricated by ultraviolet (UV) light inscribing fibre Bragg gratings (FBGs) in the SMCF, showing good spectra characteristics. Shape reconstruction is realized by the Frenet–Serret (F–S) frame and sensing characteristics such as twisting, strain and temperature are systematically analyzed. Especially, the twisting characteristics of SMCF and MCF are compared and the feasibility of self-torsional compensation of SMCF is demonstrated. In addition, shape measurement experiments with three known shapes are performed. The mean relative error (MRE) for each shape is 0.49%, 1.90% and 5.13%, respectively. These results show that the proposed sensor can accurately measure 3D shapes with temperature and twisting compensation, enabling its application prospects in the online shape feedback of continuum surgical robots. [ABSTRACT FROM AUTHOR]

Free-form optical elements are more and more broadly used in modern optical systems due to their distinctive characteristics. In order to realize the high-precision manufacturing of free-form optical element, the constraints on parameters of manufacture and measurement were established based on the designing parameters of free-form optical element. Meanwhile, the evaluation system for the machinability and detectability of free-form optical element was obtained by means of the corresponding mathematical model. Furthermore, the White Light Interference (WLI) stitching detection technology, coupled with the least square multi-parameter optimization algorithm, was used to solve shape-error measurement of free-form optical element. Additionally, a free-form surface compensation manufacturing mechanism of asymmetric shape error was established. Based on the above methods, the polynomial free-form optics were processed and measured. According to the surface shape measurement results, the same element was processed with compensation manufacturing twice. The surface shape precision was obviously improved from PV = 2553 nm and RMS = 481 nm to PV = 214 nm and RMS = 19.9 nm, which verified the effectiveness of the method. A significant value was unfolded in the engineering application of this method. [ABSTRACT FROM AUTHOR]

Shape measurements are crucial for evolutionary and developmental biology; however, they present difficulties in the objective and automatic quantification of arbitrary shapes. Conventional approaches are based on anatomically prominent landmarks, which require manual annotations by experts. Here, we develop a machine-learning approach by presenting morphological regulated variational AutoEncoder (Morpho-VAE), an image-based deep learning framework, to conduct landmark-free shape analysis. The proposed architecture combines the unsupervised and supervised learning models to reduce dimensionality by focusing on morphological features that distinguish data with different labels. We applied the method to primate mandible image data. The extracted morphological features reflected the characteristics of the families to which the organisms belonged, despite the absence of correlation between the extracted morphological features and phylogenetic distance. Furthermore, we demonstrated the reconstruction of missing segments from incomplete images. The proposed method provides a flexible and promising tool for analyzing a wide variety of image data of biological shapes even those with missing segments. [ABSTRACT FROM AUTHOR]

Accurate and reliable foot measurements at different stances offer comprehensive geometrical information on foot, thus enabling a more comfortable insole/footwear for practical use and daily activities. However, there lacks investigations on continuous deformation of foot shape during the roll-over process. This study analyses the foot deformation of 19 female diabetic patients during half weight bearing standing and self-selected walking speed by using a novel 4D foot scanning system. The scanning system has good repeatability and accuracy in both static and dynamic scanning situations. Point cloud registration for scanned image reorientation and algorithms to automatically extract foot measurements is developed. During the foot roll-over process, maximum deformation of length and girth dimensions are found at first toe contact. Width dimensions have maximum deformation at heel take off. The findings provide a new understanding of foot shape changes in dynamic situations, thus providing an optimal solution for foot comfort, function and protection. [ABSTRACT FROM AUTHOR]

Metamaterials are frequently employed as sensors in a wide range of applications because of their special qualities that are not present in nature. This study focus on the design, fabrication and measurement of a novel shape metamaterial absorber for moisture-sensing applications. The proposed metamaterial absorber consists of modified cross along with split square resonator shape conductor on top of a 0.6 mm thick substrate. Parametric studies are also performed on the different design parameters, such as the thickness of the substrate and split square resonator etc. to figure out the optimal value of design variables. The simulated results of the proposed absorber illustrate the maximum reflection coefficient at 9.9 GHz. The obtained reflection coefficient value is − 30.5 dB at the resonant frequency The measured results of the absorber also show good agreement with the simulated results. Furthermore, the proposed metamaterial-based absorber utilize as a sensor. The proposed sensor design demonstrates excellent results in terms of resonance shift, sensitivity, linearity, Q factor, and figure of merit, making it a good candidate for moisture-sensing applications. [ABSTRACT FROM AUTHOR]

The authors have recently developed a 3D shape measurement method using a combination line charge-coupled device (CCD) camera that can accurately measure 3D shapes underwater. This method can precisely measure the deformation of flexible composite marine propellers. The authors measured the deformation of a flexible model propeller fabricated with a 3D printer. To utilize the results of the deformation measurement as verification data for fluid–structure interaction calculation, not only the amount of deformation but also the deformed 3D blade shape is necessary. The authors have developed an estimation method for the deformed blade shape of flexible composite marine propellers. The authors focus on a feature that the deformed blade shape can be represented by the position change of the wing section and developed an estimation method for the deformed blade shape by image registration. To verify the system's effectiveness, model experiments were conducted in the NMRI's large cavitation tunnel using the highly skewed propeller (HSP) of a training ship "SEIUN-MARU I". Comparing the results of experiments and numerical simulation, the authors show the effectiveness of the developed estimation method. [ABSTRACT FROM AUTHOR]

The Mexican Hat wavelet (MHW) is strictly derived from the heat kernel by taking its negative first-order derivative with respect to time t. As a solution to the heat equation that the heat kernel has a clear initial condition, the Laplace–Beltrami operator. Although the MHW descriptor can effectively characterize the model information, but it has poor robustness to the model with scale transformation, and the feature description performance is affected to some extent. Following a popular mathematical method, in this paper, we bases on the MHW to study scaling invariance and proposes a new shape descriptor, the scale-invariant Mexican Hat wavelet (SIMHW), which by logarithmic sampling and Fourier transform that obtains the expression of SIMHW in Fourier domain. The experimental results show that SIMHW has finer information description ability and stronger recognition ability, and has better robustness to various non-rigid transformations. It can correctly calculate the similarity between 3D shapes and realize the effective shape retrieval. [ABSTRACT FROM AUTHOR]

Background: the development of additive manufacturing technologies (3D printing) has made it possible to manufacture complex structures such as architected materials. However, traditional inspection methods are not suited to these materials, which require volume inspection to examine their internal structure.the aim is to provide a 3D shape measurement method based on the initial computer-aided design (CAD) model used for 3D printing and X-ray radiographs.the CAD model is deformed until its virtual radiographs obtained by simulating the absorption of X-rays through the solid register with experimental radiographs. This registration is achieved by minimising a cost function with respect to the position of control points using radial basis function interpolation.the method’s performance is first evaluated using synthetic data. Its robustness is assessed with respect to image resolution, number of radiographs and noise level. Subsequently, the geometry of a solid with a tetrahedral architecture was quantified by means of a mere five radiographs. Global variation in shape and local defects in lattice structure can be detected.the method enables the in-volume shape of architected materials to be checked without reconstructing the 3D computed tomography volume, but from just a few radiographs. It is robust and can detect local defects.Objective: the development of additive manufacturing technologies (3D printing) has made it possible to manufacture complex structures such as architected materials. However, traditional inspection methods are not suited to these materials, which require volume inspection to examine their internal structure.the aim is to provide a 3D shape measurement method based on the initial computer-aided design (CAD) model used for 3D printing and X-ray radiographs.the CAD model is deformed until its virtual radiographs obtained by simulating the absorption of X-rays through the solid register with experimental radiographs. This registration is achieved by minimising a cost function with respect to the position of control points using radial basis function interpolation.the method’s performance is first evaluated using synthetic data. Its robustness is assessed with respect to image resolution, number of radiographs and noise level. Subsequently, the geometry of a solid with a tetrahedral architecture was quantified by means of a mere five radiographs. Global variation in shape and local defects in lattice structure can be detected.the method enables the in-volume shape of architected materials to be checked without reconstructing the 3D computed tomography volume, but from just a few radiographs. It is robust and can detect local defects.Method: the development of additive manufacturing technologies (3D printing) has made it possible to manufacture complex structures such as architected materials. However, traditional inspection methods are not suited to these materials, which require volume inspection to examine their internal structure.the aim is to provide a 3D shape measurement method based on the initial computer-aided design (CAD) model used for 3D printing and X-ray radiographs.the CAD model is deformed until its virtual radiographs obtained by simulating the absorption of X-rays through the solid register with experimental radiographs. This registration is achieved by minimising a cost function with respect to the position of control points using radial basis function interpolation.the method’s performance is first evaluated using synthetic data. Its robustness is assessed with respect to image resolution, number of radiographs and noise level. Subsequently, the geometry of a solid with a tetrahedral architecture was quantified by means of a mere five radiographs. Global variation in shape and local defects in lattice structure can be detected.the method enables the in-volume shape of architected materials to be checked without reconstructing the 3D computed tomography volume, but from just a few radiographs. It is robust and can detect local defects.Results: the development of additive manufacturing technologies (3D printing) has made it possible to manufacture complex structures such as architected materials. However, traditional inspection methods are not suited to these materials, which require volume inspection to examine their internal structure.the aim is to provide a 3D shape measurement method based on the initial computer-aided design (CAD) model used for 3D printing and X-ray radiographs.the CAD model is deformed until its virtual radiographs obtained by simulating the absorption of X-rays through the solid register with experimental radiographs. This registration is achieved by minimising a cost function with respect to the position of control points using radial basis function interpolation.the method’s performance is first evaluated using synthetic data. Its robustness is assessed with respect to image resolution, number of radiographs and noise level. Subsequently, the geometry of a solid with a tetrahedral architecture was quantified by means of a mere five radiographs. Global variation in shape and local defects in lattice structure can be detected.the method enables the in-volume shape of architected materials to be checked without reconstructing the 3D computed tomography volume, but from just a few radiographs. It is robust and can detect local defects.Conclusions: the development of additive manufacturing technologies (3D printing) has made it possible to manufacture complex structures such as architected materials. However, traditional inspection methods are not suited to these materials, which require volume inspection to examine their internal structure.the aim is to provide a 3D shape measurement method based on the initial computer-aided design (CAD) model used for 3D printing and X-ray radiographs.the CAD model is deformed until its virtual radiographs obtained by simulating the absorption of X-rays through the solid register with experimental radiographs. This registration is achieved by minimising a cost function with respect to the position of control points using radial basis function interpolation.the method’s performance is first evaluated using synthetic data. Its robustness is assessed with respect to image resolution, number of radiographs and noise level. Subsequently, the geometry of a solid with a tetrahedral architecture was quantified by means of a mere five radiographs. Global variation in shape and local defects in lattice structure can be detected.the method enables the in-volume shape of architected materials to be checked without reconstructing the 3D computed tomography volume, but from just a few radiographs. It is robust and can detect local defects. [ABSTRACT FROM AUTHOR]

Three-Dimensional shape measurement has been confronted with the ambiguity on the steep surface. To address the problem, compressed sensing theory is employed to reconstruct phase shifting images in DMD camera. Specially, every CCD pixel in the region of interest is aligned to N × N DMD mirrors to construct DMD camera. The one-dimensional measurement matrices are chosen to collect the measured values on CCD pixel according to the directional judgement of original gradient image. Due to the enhancement of the spatial sampling frequency and the noise robustness, the reconstructed sinusoidal stripe images are utilized to obtain the three-dimensional model of the steep surface accurately. We measure the planes with various slopes to discuss the measurement capability. The comparative experiments show that our proposed method can correct the deformed phase and repair the defect on the steep surface. [ABSTRACT FROM AUTHOR]

Background: The state-of-the-art holographic displacement measurements can only measure one dimensional displacement with one digital holography (DH) setup. To measure 3D displacements of curved diffuse objects, both 3D shape and displacement measurements are needed which requires additional optical systems and results in complex systems. Objective: In this work, we propose a digital image correlation (DIC)-assisted DH method for 3D shape measurement and 3D displacement measurement of curved diffuse objects with one DH setup. Methods: The proposed approach is based on the combination of two popular optical techniques, DH and DIC. Specfically, 3D shape is measured by tilting the illumination angle of the object wave of DH. Then the in-plane displacement component is measured with the assistance of 2D-DIC from the intensity images of DH which are laser speckle patterns in essence. At last, the out-of-plane displacement component is determined by the displacement along sensitivity vector which is measured from the phase images of DH and a displacement compensation quantity due to 3D shape and the measured in-plane displacements. Results: Hence, with the assistance of 3D shape and 2D-DIC method, 3D displacements of curved diffuse objects are measured. The metrological performance of the proposed scheme is verified by real experiments. Conclusions: The results demonstrate that the proposed DIC-assisted DH method for 3D shape measurement and 3D displacement measurement of curved diffuse objects with high accuracy. [ABSTRACT FROM AUTHOR]

Due to color object surface interference, the distortion of captured sinusoidal fringe patterns in a colorful object measurement using fringe projection profilometry causes significant phase error and therefore shape measurement error. To address the problem, an intensity correction method is proposed to correct the acquired nonsinusoidal fringe of color object and aim to improve three-dimensional (3D) reconstruction accuracy. In this paper, first, the look-up tables (LUTs) and multi-fusion matrices (MFM) are established; secondly, finding the optimal indexing value to correct the color fringe pattern for improving recognition rates and sine; finally, the corrected pattern is separated into three phase-shifting fringe patterns, which can obtain demodulation phase by the three-step phase-shifting algorithm and then recover unwrapping phase. The simulation and experimental results demonstrate that the proposed method effectively reduces the phase error of color objects and achieves complete measurement of different color regions. [ABSTRACT FROM AUTHOR]

Nonuniform sampling with equal arc length intervals can be found in shape measurements with contact sensor arrays. In this study, the conditions of nonuniform spatial sampling with an equal arc length interval are derived from two frame theorems. First, for general nonuniform sampling, the condition is that the equal arc length interval of the sensors should be less than 1 4 Ω . Second, for strictly increasing sampling (the sampling point set is strictly increasing), the condition is that the equal arc length interval of the sensors should be less than 1 2 Ω . The Ω is the maximum frequency of the detected object. For the latter, if the sampling frequency is more than twice the sampling frequency required, the reconstruction error (RRMSE and MRE) is less than 5%. If the sampling frequency is more than 2.5 times, the reconstruction error is less than 3%. The simulation and the application test are carried out, and the results show that a sensor array with equal arc length interval can reconstruct the detected object with high accuracy. [ABSTRACT FROM AUTHOR]

A de Rham p-current can be viewed as a map (the current map) between the set of embeddings of a closed p-dimensional manifold into an ambient n-manifold and the set of linear functionals on differential p-forms. We demonstrate that, for suitably chosen Sobolev topologies on both the space of embeddings and the space of p-forms, the current map is continuously differentiable, with an image that consists of bounded linear functionals on p-forms. Using the Riesz representation theorem, we prove that each p-current can be represented by a unique co-exact differential form that has a particular interpretation depending on p. Embeddings of a manifold can be thought of as shapes with a prescribed topology. Our analysis of the current map provides us with representations of shapes that can be used for the measurement and statistical analysis of collections of shapes. We consider two special cases of our general analysis and prove that: (1) if p = n - 1 then closed, embedded, co-dimension one surfaces are naturally represented by probability distributions on the ambient manifold and (2) if p = 1 then closed, embedded, one-dimensional curves are naturally represented by fluid flows on the ambient manifold. In each case, we outline some statistical applications using an H ˙ 1 and L 2 metric, respectively. [ABSTRACT FROM AUTHOR]

Objective: To evaluate the repeatability of the optical coherence tomography (OCT) retinal shape measurement with and without alignment correction in children and adults. Methods: 62 eyes of the 31 subjects were examined on the OCT with auto-alignment and alignment correction functions. We performed three measurements on each eye, created 2D retinal height maps, and extracted horizontal and vertical profiles for repeatability analysis and Legendre polynomial representation. Repeatability was determined from the average standard deviation. We estimated the refractive errors produced by the observed alignment errors. We also examined the repeatability improvement of the slopes, curvatures, and higher-order coefficients for the subjects using the Student t test. Results: Repeatability was higher in the data with alignment. We observed the average repeatability in the child group with standard deviation (SD) equal 38.20 µm in raw data, and SD = 6.11 µm in the corrected data, in adults SD = 17.04 µm in raw data, and SD = 5.22 µm in the corrected data. The slope repeatability improved in both child [horizontal t (18) = 4.62, p < 0.001 and vertical t (17) = 4.43, p < 0.001] and adult groups [t (18) = 2.73, p = 0.007 and vertical t (26) = 2.14, p = 0.02], while higher-order coefficients were not affected. Conclusions: Alignment correction improved repeatability of the OCT retinal shape measurements, especially for child subjects. Curvature and higher-order distortions were not affected by the alignment error. The refractive errors produced by alignment errors are low, and the model can be used to estimate the peripheral refraction. [ABSTRACT FROM AUTHOR]

Introduction and hypothesis: Urethral closure mechanism dysfunction in female stress urinary incontinence (SUI) is poorly understood. We aimed to quantify these mechanisms through changes in urethral shape and position during squeeze (voluntary closure) and Valsalva (passive closure) via endovaginal ultrasound in women with varying SUI severity. Methods: In this prospective cohort study, 76 women who presented to our tertiary center for urodynamic testing as preoperative assessment were recruited. Urodynamics were performed according to International Continence Society criteria. Urethral pressures were obtained during serial Valsalva maneuvers. Urethral lengths, thicknesses, and angles were measured in the midsagittal plane via dynamic anterior compartment ultrasound. Statistical shape modeling was carried out by a principal component analysis on aligned urethra shapes. Results: Age, parity, and BMI did not vary by SUI group. Ultrasound detected a larger retropubic angle, urethral knee-pubic bone angle (a novel measure developed for this study), and infrapubic urethral length measurements at Valsalva in women with severe SUI (p = 0.016, 0.015, and 0.010). Shape analysis defined increased "c" shape concavity and distal wall pinching during squeeze and increased "s" shape concavity and distal wall thickening during Valsalva (p < 0.001). It also described significant urethral shape differences across SUI severity groups (p < 0.001). Conclusions: Dynamic endovaginal ultrasound can visualize and allow for quantification of voluntary and passive urethral closure and variations with SUI severity. In women with severe SUI, excessive bladder neck and distal urethra swinging during Valsalva longitudinally compressed the urethra, resulting in a proportionally thicker wall at the mid-urethra and urethral knee. [ABSTRACT FROM AUTHOR]

With the rapid development of high-speed image sensors and optical imaging technology, these have effectively promoted the improvement of non-contact 3D shape measurement. Among them, striped structured-light technology has been widely used because of its high measurement accuracy. Compared with classical methods such as Fourier transform profilometry, many deep neural networks are utilized to restore 3D shape from single-shot structured light. In actual engineering deployments, the number of learnable parameters of convolution neural network (CNN) is huge, especially for high-resolution structured-light patterns. To this end, we proposed a dual-path hybrid network based on UNet, which eliminates the deepest convolution layers to reduce the number of learnable parameters, and a swin transformer path is additionally built on the decoder to improve the global perception of this network. The experimental results show that the learnable parameters of the model are reduced by 60% compared with the UNet, and the measurement accuracy is not degraded at the same time. The proposed dual-path hybrid network provides an effective solution for structured-light 3D reconstruction and its practice in engineering. [ABSTRACT FROM AUTHOR]

Fringe projection profilometry (FPP) is a technique used for obtaining the three-dimensional shape of an object in fields such as reverse engineering, cultural heritage, and computer vision. The FPP measurement accuracy significantly depends on the arrangement of the measurement system, measurement space conditions, equipment setting, and object characteristics. However, experimental verification of the measurement conditions is time-consuming and expensive. This study presents a simulator that can set a broader range of measurement conditions. This simulator was developed using Unity, which is an integrated development environment for video games. The proposed simulator can be configured with a graphical user interface for device placement and operation, and it can freely adjust the aperture, exposure time, and depth-of-field of the camera. The measurement simulation results for a CAD model obtained using the proposed simulator are presented. The results indicate that camera defocus or unfit exposure time causes phase measurement errors. [ABSTRACT FROM AUTHOR]

Precision interference measurements of the shape parameters of optical surfaces are one of the most important types of measurements in the field of geometric quantities. In the countries participating in this research, special primary standards are involved in the reproduction and transmission of a unit of length to measuring instruments. To declare and confirm the measuring and calibration capabilities of the national metrological institutes of Belarus, Russia and Ukraine in the field of interference measurements of the parameters of deviation from flatness in the period of 2015–2018, additional comparisons COOMET.L-S15 have been carried out. The article presents the results of these comparisons. In accordance with the current rules, in 2020, the International Bureau of Weights and Measures, based on the data on the examination of the results of comparisons carried out by leading experts from a number of regional metrological organizations, introduced data on the results obtained into the international database CIPM MRA. The results of the comparisons allowed Belarus and Russia to declare, and Ukraine to confirm their measuring and calibration capabilities in the CIPM MRA database. [ABSTRACT FROM AUTHOR]

The aim of this study is to estimate the thermal diffusivity of martensitic and austenitic microstructures of a NiTi SMA. To this end, an experimental apparatus supported on the Angstrom's method was designed, where one face of a cylindrical sample is subjected to a periodic heat flux and the other face is kept at a constant temperature. This apparatus was developed to provide the three fundamental requirements of the applied method: (1) uniformity of the thermal field in any cross section of the medium; (2) complete damping of the heat wave before it reaches the face at a prescribed temperature; (3) thermophysical properties independent of temperature within the adopted measurement range. Fourteen thermocouples are fixed at specific locations on the side of the sample, for measuring the amplitude and phase-lag of the thermal wave supplied from periodic heating at a certain frequency. The measurements of these parameters, carried out on a permanent periodic regime, are replaced into a mathematical model, in order that the thermal diffusivity can be determined by linear regression. The results obtained for the two microstructures showed good agreement with the literature, with absolute deviations below 8.5 %, proving the effectiveness of the experimental arrangement. The estimated thermal diffusivity of austenite is 48.21 % higher than that of martensite. The uncertainty quantification, assessed by the Monte Carlo Method, indicates a low dispersion, below 1.5 %, which delivers high precision and reliability to the estimated thermophysical property. [ABSTRACT FROM AUTHOR]

Autoclave processing is the most common method used for curing thermoset prepregs due to its capability to minimize void content. However, unresolved problems still exist in the prepreg manufacturing process, such as the inconsistent thickness, pores, voids, and resin-rich areas of the laminate panel. Until now, laminate thickness, resin distribution, and fiber wrinkling have been the key issues that have caught the attention of many researchers. In this review paper, defect-related factors involved in the manufacturing of complex laminated composites are identified, starting with the layup process itself and ending with the curing process. The occurrence rate of defects in complex shape laminate is affected by several factors, including mold selection, material characteristics, bagging configuration, and stacking sequence. The vacuum bagging process needs further attention as it has been identified as the most critical process following its high contribution to the issues of void content and resin accumulation. Various methods for quality measurements of complex shape laminate were also described in this review, specifically for the aspects of thickness uniformity, resin distribution, and inter-laminar defects. [ABSTRACT FROM AUTHOR]

A measurement system based on the Scheimpflug principle is designed in this paper to solve the problem of difficulty in clear imaging due to excessively small depth of field in line-structured light close-range photogrammetry. A conversion model from the image coordinate system to the measured object coordinate system is established through the spatial projection relationship. The calibration method of the measurement system under Scheimpflug conditions is investigated and the calibration of the measurement system is completed through nonlinear iterative optimization, and the calibration re-projection error is less than 0.3 pixels. GPU (graphic processing unit) acceleration processing is performed on the center extraction of line-structured light stripe to achieve real-time output at a high frame rate. The processing time for a single 1024 × 1280 image is only 2.14 ms after acceleration. Experimental results showed that the measurement system can realize the three-dimensional measurement of complex shapes and high-reflectivity surfaces with high detection accuracy and output frame rate. [ABSTRACT FROM AUTHOR]

The vital sensing parameter on self-sensing actuation in the spring form of shape memory alloy (SMA) is determined through experimental analysis. A unique measurement technique is adopted that interlinks the electro–thermo–mechano features during the shape memory effect in NiTi, NiTiCu, and NiTiFe springs. The influence of the spring index, the number of active turns, material composition, and transition temperature is assessed. SMA spring's effective functional behavior to be used as an actuator and or a sensor is ensured via the measurement of electrical parameters—the resistance, inductance, and impedance variations revealed during the solid–solid phase change, i.e., displacement. However, the spring form of SMA would exhibit variation in inductance and a variation in electrical resistance, which in turn is considered a variation in the electrical impedance, which may also be appropriate sensing information. The thermo-mechanical and thermo-electrical measurements are synchronized using an impedance analyzer and data acquisition module with a specific programming technique. The active spring is equivalently a series resistance–inductance circuit, since the collective effect of a decrease in resistance and increase in inductance with an increase in temperature offers increased L R and vice versa to support structural health monitoring. [ABSTRACT FROM AUTHOR]

Research regarding the similarity measurements of 3D craniofacial models (including 3D skull and face models) is an important research direction in fields such as archaeology, forensic science, and anthropology and represents a meaningful and challenging task. Its major challenges are the fact that 3D skulls are geometric models with multiple holes and complex topologies, there are facial expression changes on the 3D faces. Therefore, the general 3D shape similarity measurements, which are sensitive to boundaries and expression changes, make it impossible to simultaneously measure skull and face similarity. In this paper, we define a 3D signature to describe the pure intrinsic structure and distinguish the similar basic shape and complex topology of 3D skulls and faces: the harmonic wave kernel signature (HWKS). The HWKS is a point descriptor involving the Laplace–Beltrami operator, which is able to effectively extract geometrical and topological information from 3D skulls and faces. Based on the HWKS, we provide an effective pipeline for 3D skull and face similarity measurement by calculating the cosine distance between the HWKS values of 3D skulls and faces. By making comparisons with the wave kernel signature, the HWKS simultaneously describes both local and global properties of a shape. Results from a number of experiments have already shown that our framework is suitable for both measure 3D skull similarity and face similarity, and more importantly, measuring skull similarity and face similarity are two independent processes although using the same framework. By using the same measurement method for 3D skull similarity and face similarity, we observe an effective craniofacial relationship under unified metrics: The change rate of skull similarity is generally consistent with the corresponding face similarity, indicating the correlation between the shape of the 3D skull and its corresponding 3D face shape. And our experimental results show the rationality and effectiveness of this method, which refers to the previous researchers measure the similarity of the reconstructed face from the original skull to reflect the similarity of the original skull. [ABSTRACT FROM AUTHOR]

A three-dimensional (3D) shape measurement method based on speckle-embedded fringe patterns (composite fringe patterns) and wrapped phase-to-height lookup table (LUT) is proposed. As an auxiliary signal, speckle is embedded into the phase domain of the projected fringes, and the wrapped phase and deformed speckle modulated by the objects are demodulated by phase-shifting algorithm. With the assistance of the LUT established in advance, the candidate heights are directly obtained by the wrapped phase. Subsequently, the speckle correlation is used to eliminate the height ambiguity, and then the absolute spatial height of the measured objects can be reconstructed without projecting any additional pattern. In this paper, the cooperation of embedded speckle and LUT allows the speckle to do correlation operation in some certain smaller area of the candidate heights' location, instead of matching within the whole measurement range, thus it can improve the computational efficiency in the determination of the unique accurate height. Theoretical analysis and experimental results have demonstrated that the proposed method can achieve high-accuracy and robust 3D shape measurement of dynamic and static complex scenes. [ABSTRACT FROM AUTHOR]

Ultra-cold atom experiment in space with microgravity allows for realization of dilute atomic-gas Bose-Einstein condensate (BEC) with macroscopically large occupation number and significantly long condensate lifetime, which allows for a precise measurement on the shape oscillation frequency by calibrating itself over numerous oscillation periods. In this paper, we propose to measure the Newtonian gravitational constant via ultra-cold atom BEC with shape oscillation, although it is experimentally challenging. We also make a preliminary perspective on constraining the modified Newtonian potential such as the power-law potential, Yukawa interaction, and fat graviton. A resolution of frequency measurement of (1 - 100) nHz at most for the occupation number 10 9 , just one order above experimentally achievable number N ∼ 10 6 - 10 8 , is feasible to constrain the modified Newtonian potential with Yukawa interaction greatly beyond the current exclusion limits. [ABSTRACT FROM AUTHOR]

This study aims to investigate the morphological characteristics of mature follicles with clinical value. The five morphological indexes of follicles in 72 natural ovulation cycles were measured. The shoot time of follicle photos was the day before ovulation. Measurement software was the MATLAB Image Processing Toolbox. The measured average area, perimeter, equivalent circle diameter, and roundness were 301.29 ± 8.52 mm2, 62.23 ± 6.82 mm, 20.21 ± 3.08 mm, and 0.89 ± 0.05, respectively; and the maximal diameter was 23.12 ± 3.06 mm. Image Processing Toolbox is a simple and convenient measurement software. The standardization of the reference indexes of follicular morphology has important clinical application value in reproductive medicine. [ABSTRACT FROM AUTHOR]

Shape and attitude of resident space objects directly affect the orbit propagation via drag and solar radiation pressure. Obtaining information beyond an object state is integral to identifying an object, aid in tracing its origin and its capabilities. For objects that have a significant distance to the observer, only non-resolved imaging is available, which does not reveal any details of the object. So-called non-resolved light curve measurements, i.e. brightness measurements over time, can be used to determine the shape of convex space objects using an inversion scheme. The inversion process starts by first determining the Extended Gaussian Image and then solving Minkowski problem to obtain the closed shape result. In this paper, the effect of measurement noise on the shape inversion and the influence of the measurement geometry is investigated. Despite the presence of measurement noise, in a new methodology, expanding upon established inversion techniques, almost perfect inversion results can be obtained in a two-step process: first, an initial light curve is used for shape hypothesis creation, and then, a second (potentially very short) light curve is used for selection of the best hypothesis. Results are shown for two standard shapes of a cuboid and a house shape. [ABSTRACT FROM AUTHOR]

Purposes: The main purpose of this study was to assess the measurements and shape of the sella turcica by using cone beam computed tomography (CBCT) and to associate the data to skeletal class II and class III patients, including correlations with gender, age and measurements of the anterior cranial base. Material and methods: A trained examiner specialist in dental radiology selected and evaluated randomly 95 CBCT images of pre-orthognathic surgery patients, 60 (63.2%) being female and 35 (36.8%) male with age between 16 and 57 years. All images were evaluated to determine the size, shape and volume of the sella turcica. The anterior cranial base, represented by the S–N line (sella–nasion), was also measured. Results: Of these 95 patients, 48 (50.5%) had class III facial skeletal pattern, whereas 47 (49.5%) had class II. No statistically significant differences were found between class II and class III patients in the measurements and shape of the sella turcica (P > 0.05). The diameter and volume of the sella turcica had higher values in female patients, whereas the measurements of the anterior cranial base were higher in males (P < 0.05). Conclusion: Therefore, one can conclude that measurements of the sella turcica are not reliable parameters to evaluate whether a class II or class III patient will or will not need orthognathic surgery. [ABSTRACT FROM AUTHOR]

This work addresses two main contributions for shape measurement: First, a new circularity measure for planar shapes is introduced based on their geometrical properties in the projection space of Radon transform. Second, a general-purpose evaluation criterion, power of discrimination, for assessing the efficiency of a shape measure is proposed. The new measure ranges over the interval [0, 1] and produces the value 1 if and only if the measured shape is a perfect circle. The proposed measure is invariant with respect to translation, rotation and scaling transformations. Moreover, it is also robust against border distortion of shapes. It is theoretically well founded and can be extended to other problems of shape measurement. Our approach can deal with complex shapes composed of connected components that cannot be handled by classical contour-based methods. Several experiments show its good behavior and demonstrate the efficiency and applicability of our proposed measure. Finally, we also consider our proposed evaluation criterion for assessing different circularity measures. [ABSTRACT FROM AUTHOR]

MetroBeta, a recently completed European Metrology Research Project, aimed at the improvement of the knowledge of the shapes of beta spectra, both in terms of theoretical calculation and measurement. The most prominent experimental work package concerned the measurement of the spectrum shapes of several beta decaying radionuclides by means of metallic magnetic calorimeters (MMCs) with the beta emitter embedded in the absorber. New MMC chips were designed and optimized for five different absorber heat capacities, enabling the measurement of beta spectra with Q values ranging from few tens of keV up to ~ 1 MeV. Several beta spectra were measured with high energy resolution and statistics of up to 107 counts. [ABSTRACT FROM AUTHOR]

We propose a process technology that can be applied to a variety of applications by machining existing lenses to create an optical system required for research by modifying commercial glass optical systems. A 1-in. hole was created in an LF5 glass lens by drilling, followed by spiral grinding, and finally, precision spiral grinding. In addition, cracking and chipping were analyzed according to the processing process and optimized process conditions. We fabricated an achromatic doublet lens with a diameter of 50.8 mm, focal fa of 75 mm and fba of 65.7 mm, under optimized processing conditions. The processed lenses were determined by measuring the surface geometry of the lenses using ASI, and the lenses were inspected internally using OCT and dark field measurements to verify the internal sectional cracks and chipping of the lenses. The results confirm that there are no problems with the use of the hole in the existing glass lens as an optics. In addition, the manufactured lens will be available as an integrated optical system that can combine lenses with mirrors or detectors to create small systems and multi-axial views. [ABSTRACT FROM AUTHOR]

We consider problems estimating measurement uncertainty for shape deviations in planar surfaces of large parts using the reference plane method. The sources of uncertainty in the implementation of various measurement schemes by this method are analyzed. The schemes are determined by the methods of realization of the output base – the plane defined by the three reference points of the supporting platform of the measuring system, as well as the methods of obtaining and processing primary measurement information. The results of experimental studies of the accuracy of a multisensor system designed to assess the topography of the flat surfaces of mechanical elements of particle accelerators are presented. [ABSTRACT FROM AUTHOR]

This paper proposes a method of generating 3D building models with precise geospatial information and a photograph-based façade appearance from panoramic image sequences and digital maps. 3D building modeling research is actively being conducted in areas such as geographic information systems, virtual reality, and augmented reality. However, the generation of realistic 3D models from a ground-level viewpoint is still extremely costly in terms of labor of modeling experts, and collection of data. We have developed a method for 3D building modeling with high-resolution photograph-based appearance information using panoramic images captured at ground level with a mobile mapping system, and geospatial information obtained from a digital map. The proposed method includes 1) pre-processing for tilt correction and base 3D model generation, 2) geo-registration of panoramic images with minimal user input, and 3) building height and shape estimation. This paper presents the proposed method and the quantitative performance measure obtained from a developed test modeling system. In addition, modeling results from an experimental dataset are also presented. [ABSTRACT FROM AUTHOR]

Most modern mobile devices are equipped with touchscreens as the main input hardware. Users can write text or draw shapes on the touchscreen to interact with apps. Therefore, accurate recognition of users’ freehand sketches becomes crucial for a device to receive correct instructions from users. This paper proposes a real-time scheme to recognize shapes drawn on the touchscreen. The proposed shape recognition scheme includes preprocessing, feature extraction and shape classification stages. Freehand strokes drawn by users are usually distorted and inaccurate. In preprocessing, this study uses the sampling technique to remove drawing imperfections such as small jagged noise or distorted strokes. In the feature extraction, we use a state machine to extract the length and curvature as the intrinsic features of a shape. In the final shape classification stage, a template-based approach is used to classify the input shape. A fitness score of the input shape to a template is calculated and the template with the highest score is chosen as the most matched shape. Experiment results show that the proposed real-time shape recognition has high accuracy and good performance. [ABSTRACT FROM AUTHOR]

This paper presents a novel base-points-driven shape correspondence (BSC) approach to extract skeletons of articulated objects from 3D mesh shapes. The skeleton extraction based on BSC approach is more accurate than the traditional direct skeleton extraction methods. Since 3D shapes provide more geometric information, BSC offers the consistent information between the source shape and the target shapes. In this paper, we first extract the skeleton from a template shape such as the source shape automatically. Then, the skeletons of the target shapes of different poses are generated based on the correspondence relationship with source shape. The accuracy of the proposed method is demonstrated by presenting a comprehensive performance evaluation on multiple benchmark datasets. The results of the proposed approach can be applied to various applications such as skeleton-driven animation, shape segmentation and human motion analysis. [ABSTRACT FROM AUTHOR]

The modern construction industry makes use of innovative production and assembly technologies, whose purpose is to implement reliable and simple structures. One product of such technologies is an arch-shaped steel sheet section that might be used as a self-supporting covering for general construction and industrial building construction. Considering complex geometry and boundary conditions, the FEM model of this structure is sophisticated and may contain errors. This paper presents numerical approaches for the calculation of sheet metal section elements of such coverings, namely two numerical approaches that differ in detailing of the properties of considered physical object. The first approach is based on a model that is characterized by simplified geometry and boundary conditions. The second scenario concerns a detailed FEM model with actual geometry captured by a laser triangulation method, experimentally determined material stress–strain relationship, and load conditions measured on an experimental stand. The results obtained with the use of computer simulations based on both approaches described above and experimental results are compared. The errors caused by simplification of the first numerical model are discussed. Finally, an acceptable reduction of FEM model complexity is proposed for the analyzed structure. [ABSTRACT FROM AUTHOR]

Binary pattern defocused projection method can overcome the nonlinear gamma of the projector, as well as filter high harmonics and high-frequency noise. However, high-accuracy three-dimensional (3-D) shape measurement of complex surface using it still remains a challenge. Therefore, a novel Gray code plus phase-shifting method based on defocusing is proposed to solve the problem. The edges of Gray code patterns become blurred owing to defocus, which makes the recovery of accurate Gray code patterns difficult. To solve this problem, the positive and inverse Gray code patterns are projected to obtain threshold values, which are used to achieve the binarization of Gray code patterns. This method is robust and suitable for different defocus levels. Compared with the traditional Gray code plus phase-shifting method, the experimental results prove the effectiveness and feasibility of the proposed method. [ABSTRACT FROM AUTHOR]

Recovering the 3D shape of a non-rigid object is a challenging problem. Existing methods make the low-rank assumption and do not scale well with the increased degree of freedom found in complex non-rigid deformations or shape variations. Moreover, in general, the degree of freedom of deformation is assumed to be known in advance, which limits the applicability of non-rigid structure from motion algorithms in a practical situation. In this paper, we propose a method for handling complex shape variations based on the assumption that complex shape variations can be represented probabilistically by a mixture of primitive shape variations. The proposed model is a generative probabilistic model, called a Procrustean normal distribution mixture model, which can model complex shape variations without rank constraints. Experimental results show that the proposed method significantly outperforms existing methods. [ABSTRACT FROM AUTHOR]