Light Plane Research Articles

Research on calibration method for line-structured light sensor based on spatial quadratic surface fitting

Abstract The calibration of the light plane serves as the fundamental prerequisite for accurate three-dimensional (3D) measurement using line-structured light sensor (LSLS). Aiming at the problem that the light plane projected by the line laser is not an ideal plane, this paper proposes an LSLS calibration method based on spatial quadratic surface fitting. In the LSLS measurement model, the standard conical quadratic surface equation is used to replace the plane equation in the traditional measurement model to solve the 3D coordinates of the light stripe. In the LSLS calibration process, the spatial standard conical quadratic surface fitting algorithm is also used to replace the traditional plane equation fitting method to achieve structural parameter calibration. The calibration experiment results based on general LSLS show that the calibration method described in this paper improves the fitting accuracy by 15.38% and the 3D measurement accuracy by 13.33% compared with the traditional calibration method based on light plane fitting. This not only provides a high-precision measurement solution for low-cost LSLS, but also enables its application in 3D measurements in the presence of lens refraction, where the improvement in accuracy may be even more significant.

Research on the visual measurement algorithm of cam base circle radius based on virtual structured light plane

Abstract Using line structured light vision measurement technology, it is possible to perform non-contact measurement of the cam's base circle radius. To address the issue of the structured light plane not being perpendicular to the axis of the cam being measured, this paper obtains the axis equation of the cam being measured through calibration, and based on the axis equation, it obtains the spatial equation of a virtual light plane that is perpendicular to the axis. The point cloud on the surface of the cam is projected onto the virtual plane, and the base circle radius of the cam is obtained using the coordinates of the projected points. To improve the measurement accuracy of the cam's base circle radius, this paper designs a base revision model to address measurement errors caused by the non-coincidence of bases. The measurement results of the base circle radii of four cams on the engine camshaft show that the line structured light vision measurement technology meets the measurement requirements and is feasible for non-contact measurement.The innovation presented herein lies in the development of a cloud acquisition model predicated on line structured light vision technology, which effectively converts a complex spatial curve fitting challenge into a simpler planar curve fitting problem.This transformation not only streamlines the measurement process for the cam base circle radius but also significantly enhances the measurement precision of engine camshafts.

Complexes of Hexacoordinated Ni(II) Based on Diacetyl <i>bis</i>-hetarylhydrazones: Structures and Magnetic Properties

Mononuclear nickel complexes [NiL1(NCS)2] ⋅ 2DMSO (I), [NiL1(NCS)2] ⋅ DMF (II), and [NiL2(NCS)2] ⋅ 0,5CH3OH ⋅ 1,5H2O (III) with the distorted octahedral coordination node, where L1 and L2 are the tetradentate ligand systems derived from the products of the condensation of diacetyl with 2-hydrazinoquinoline and 2-hydrazino-4,6-dimethylpyrimidine, respectively, are synthesized. The structures of the compounds are determined by IR pectroscopy and XRD (CIF files ССDС nos. 2219793 (I), 2142035 (II), and 2219794 (III)). The quantum chemical modeling of the axial parameter of magnetic anisotropy in the zero field (D) is performed for the synthesized compounds in the framework of the SA-CASSCF+NEVPT2 method. The complexes are shown to be characterized by three-axis magnetic anisotropy close to the light magnetization plane with positive D. The axial parameter of magnetic anisotropy (Dexp = 8.79 cm–1) determined by the approximation of the magnetometry data on complex [NiL2(NCS)2] ⋅ 0,5CH3OH ⋅ 1,5H2O is consistent with the calculated value (Dcalc = 11.5 cm–1).

Photochemistry with Plane-Polarized Light: Controlling Selectivity of a Photochemical Rearrangement.

Over the past 50 years, a principal approach to controlling conventional photochemical reactions has relied on imposing geometric constraints on reactant or transition state via conducting photochemistry in the organized or constraining media. Herein, we describe a fundamentally different approach to affect the course of photochemical reactions (photochemical rearrangements) by utilizing spatially selective excitation of specific electronic transitions with plane-polarized light in the reactant molecules uniformly aligned in the nematic liquid crystal phase. In particular, we focused on the Type B enone rearrangement of 4,4-diarylcyclohexenones - one of the most common photochemical rearrangements. We demonstrated that the aryl migratory aptitude in this reaction was attenuated in response to changing an angle between the polarization plane of the incident light and the alignment direction of the nematic liquid crystal, with the enhanced aryl migration achieved when the polarization plane coincided with the transition dipole moment leading to the excited state responsible for this migration. The spatially-selective initial excitation therefore was overruling the electronic factors responsible for the relative ratio of the two alternative photoproducts. The experimental findings were further supported by the results of a computational study. This work showcases a new fundamental paradigm in controlling photochemical reactivity and selectivity of photoreactions.

Single-Shot, Monochrome, Spatial Pixel-Encoded, Structured Light System for Determining Surface Orientations

This study introduces a technique for determining surface orientations by projecting a monochrome, spatial pixel-encoded pattern and calculating the surface normals from single-shot measurement. Our method differs from traditional methods, such as shape from shading and shape from texture, in that it does not require relating the local surface orientations of adjacent points. We propose a multi-resolution system incorporating symbols varying in sizes from 8 × 8, 10 × 10, 12 × 12, 14 × 14, and 16 × 16 pixels. Compared to previous methods, we have achieved a denser reconstruction and obtained a 5.2 mm resolution using an 8 × 8 pattern at a depth of 110 cm. Unlike previous methods, which used local point orientations of grid intersection and multiple colors, we have used the monochrome pattern and deterministic centroid positions to compute the unit vector or direction vector between the neighboring symbols. The light plane intersections are used to calculate the tangent vectors on the surface. Surface normals are determined by the cross-product of two tangent vectors on the surface. A real experiment was conducted to measure simple plane surfaces, circular surfaces, and complex sculptures. The results show that the process of calculating surface normals is fast and reliable, and we have computed 1654 surface normals in 29.4 milliseconds for complex surfaces such as sculptures.

Method of automatic calibration and measurement of the light polarisation plane rotation with tilted fibre Bragg grating and discrete wavelet transform usage

Method of automatic calibration and measurement of the light polarisation plane rotation with tilted fibre Bragg grating and discrete wavelet transform usage

Multi-line laser 3D reconstruction method based on spatial quadric surface and geometric estimation

The traditional multi-line laser 3D reconstruction is based on binocular epipolar constraints and the equation of the laser optical plane. Firstly, matching points are identified based on the epipolar constraints. Then, the correct matching points are selected based on the optical plane equation of the multi-line laser. Finally, 3D reconstruction is performed using the selected matching points. In actual production processes involving multi-line lasers, noticeable distortion occurs due to the projection of Diffractive Optical Elements (DOE) at a large angle. This results in curved laser light planes and curved reflections on the measured objects. Under such circumstances, efficiently screening matching points using the traditional method based on the laser plane equation becomes challenging. Additionally, inherent noise in multi-line laser systems introduces errors in extracted laser center coordinates, making it impossible to directly obtain high-precision 3D data. To address these issues, this paper proposes a method that utilizes spatial quadric surfaces and geometric estimation for completing multi-line laser 3D reconstructions. By analyzing the distortion principle of DOE and the positional relationship after optical diffraction, the multi-line laser manifests as a quadric surface on the optical output plane. Consequently, by calibrating the equations of the quadric surface and applying binocular polar constraints, suitable matching points for the multi-line laser can be chosen. Once an accurate matching point is identified, a minimum geometric distance estimation can be established based on the distance constraint between the point and its corresponding epipolar line. This distance represents the separation between the left and right camera’s laser center points and their respective epipolar lines. Utilizing this estimate of the minimum geometric distance, a refined calculation can be performed to better satisfy epipolar constraints and obtain new matching points. Ultimately, utilizing these new matching points enables the completion of 3D reconstruction for multi-line lasers. In comparison with methods relying on spatial plane and epipolar constraints, our algorithm exhibits a superior degree of matchability and accuracy.According to multiple groups of test data, the average error before optimization is 0.3126 mm, and can be increased to 0.0336 mm after optimization.

The shading isophotes: Model and methods for Lambertian planes and a point light

Structure-from-Motion (SfM) and Shape-from-Shading (SfS) are complementary classical approaches to 3D vision. Broadly speaking, SfM exploits geometric primitives from textured surfaces and SfS exploits pixel intensity from the shading image. We propose an approach that exploits virtual geometric primitives extracted from the shading image, namely the level-sets, which we name shading isophotes. Our approach thus combines the strength of geometric reasoning with the rich shading information. We focus on the case of untextured Lambertian planes of unknown albedo lit by an unknown Point Light Source (PLS) of unknown intensity. We derive a comprehensive geometric model showing that the unknown scene parameters are in general all recoverable from a single image of at least two planes. We propose computational methods to detect the isophotes, to reconstruct the scene parameters in closed-form and to refine the results densely using pixel intensity. Our methods thus estimate light source, plane pose and camera pose parameters for untextured planes, which cannot be achieved by the existing approaches. We evaluate our model and methods on synthetic and real images.

Flexible technique for global calibration of multi-view stereo vision with a non-overlapping FOV using linear structured light projector.

A flexible global calibration method for multi-view stereo vision with non-overlapping field of view (FOV) using linear structured light projector is presented in this paper. At least three groups of linear structured light plane equations are utilized to calculate the rotation between any pair of cameras with non-overlapping FOV, and then the closed solution of the translation is determined based on the constraint that the normal vector is perpendicular to the lines on linear structured light plane. Once the rotation and translation between all pairs of cameras with non-overlapping FOV are obtained, the rotation and translation of each camera relative to the reference position is eventually computed through global optimization. The experimental data reflects that the calibration accuracy is improved by 35.2% after global optimization, and the global calibration results of the proposed method deviates less from that of Zhang's method.

Tunnel excavation slag volume measurement using triple-line structured-light vision: Rectification and optimization

The precise measurement of excavated tunnel slag volume is crucial for tunnel boring machine construction security and optimizing. Structured-light vision measurement method is a widely employed method for volume measurement of convey belt, comprising a camera and laser projector. However, maintaining alignment between the structured light plane and the belt is challenging, especially with machine vibrations, leading to significant errors in slag volume measurement. To address this problem, we propose an innovative excavated tunnel slag volume measurement method based on triple-line structured light vision. After capturing images with multiline structured light, our approach encompasses extracting centerlines, profile three-dimensional conversion, calibrating profile distortions with arbitrary structured light layouts, and registering to obtain the area of the structured light section. Finally, integral calculations along the movement speed of conveyor belt yield accurate, real-time measurements of tunnel slag volume. Extensive experiments in factory and construction site settings confirm the real-time capabilities, accuracy, and universal applicability of our approach.

A calibration method of line-structured light system for measuring outer circle dimension during machining

The line-structured light system is widely utilized for various 3D profile measurements due to its convenience and high efficiency. However, the existing calibration methods primarily focus on establishing the relationship between object points and image points, which imposes stringent requirements on the calibration target. To address this issue, a practical calibration method based on interpolation function is proposed in order to measure a specific 3D profile - namely, the diameter of a rotating workpiece during machining. Firstly, the light stripe projected onto an ordinary machined workpiece by a light plane is captured using a Charge-Coupled Device (CCD) camera and subsequently fitted to a quadratic elliptic curve after undergoing image processing. Subsequently, the cubic spline interpolation function is selected to directly establish a mapping relationship between geometric characteristics of the elliptic curve and the diameter measurement. Several experiments are conducted to evaluate the proposed methods. The experimental results demonstrate that compared with two comparison methods, our approach reduces the calibration error of linear structured light systems by 69 % and 51 %, respectively; furthermore, it enables restoration of smooth and detailed 3D models through parallel movement of the system. Moreover, our entire calibration process proves practicable in simplifying experimental procedures while remaining suitable for industrial inspection applications.

Quantum effects in the interaction of low-energy electrons with light.

The interaction between free electrons and optical fields constitutes a unique platform to investigate ultrafast processes in matter and explore fundamental quantum phenomena. Specifically, optically modulated electrons in ultrafast electron microscopy act as noninvasive probes that push space-time-energy resolution to the picometer-attosecond-microelectronvolt range. Electron energies well above the involved photon energies are commonly used, rendering a low electron-light coupling and, thus, only providing limited access to the wealth of quantum nonlinear phenomena underlying the dynamical response of nanostructures. Here, we theoretically investigate electron-light interactions between photons and electrons of comparable energies, revealing quantum and recoil effects that include a nonvanishing coupling of surface-scattered electrons to light plane waves, inelastic electron backscattering from confined optical fields, and strong electron-light coupling under grazing electron diffraction by an illuminated crystal surface. Our exploration of electron-light-matter interactions holds potential for applications in ultrafast electron microscopy.

Dead-zone-free atomic magnetometer based on hybrid Poincaré beams

In this paper, we present the experiment and the theory scheme of light-atom interaction in atomic magnetometers by using a hybrid Poincaré beam (HPB) to solve an annoying problem, named “dead zone.” This kind of magnetometer can be sensitive to arbitrary directions of external magnetic fields. The HPB has a complex polarization distribution, consisting of a vector radially polarized beam and a scalar circularly polarized beam in our experiment. These two kinds of beams have different directions of dead zones of external magnetic fields; thereby, the atomic magnetometer with an HPB can avoid the non-signal area when the direction of the external magnetic field is in the plane perpendicular to the light polarization plane. Furthermore, the optical magnetic resonance (OMR) signal using an HPB still has no dead zones even when the direction of the external magnetic field is in the plane parallel to the polarization plane in our scheme. Our work has the potential to simplify and optimize dead-zone-free atomic magnetometers.

Line structure light calibration based on a freely placed single cylindrical object

The traditional Zhang calibration method takes multiple checkerboard images at different positions, but in practical applications, surface measurement is usually required, in which case the planar target is not suitable. Thus, a calibration method is needed, using curved surface targets. In this paper, a line-structured light calibration method is presented based on a freely placed cylindrical object. The calibration process is as follows: the cylindrical target is placed freely and irradiated with a laser; The camera captures the target image and then the light strips of the cylindrical target and its two bus bars are extracted; The translation relation between the cylinder and the images is calculated according to the imaging principle and geometric relation; The center points of the light strip are converted to 3D coordinates according to the internal parameters of the camera for fitting the light plane. Two experiments are designed to verify the advantages of the method. The needle gauge experiment shows that 0.001 mm accuracy can be achieved in a single frame measurement, and the ring gauge experiment shows that the measurement accuracy of the system is increased by 20 %. This method is more applicable and more suitable than the traditional method for high-precision industrial 3D measurement.

Interactive calculation of light refraction and caustics using a graphics processor

While modern rendering systems are effective at modeling complex light paths in complex environments, rendering refractive caustics still takes a long time. Caustics are light patterns that occur when light is refracted and reflected from a surface. Due to the sharp density distribution of these mirror events, rendering algorithms mainly rely on direct sampling of the bidirectional scattering distribution function on these surfaces to plot trajectories. This requires many calculations. Photonic maps are also used. However, there are problems limiting the applicability of caustic maps. Since each photon in the photon buffer must be processed, therefore, one has to choose between a strongly underestimated caustic sampling and a large decrease in speed in order to use a sufficient number of photons for caustics in order to obtain high-quality images. Complex mirror interactions cause oversampling in bright focal areas, while other areas of the caustic map remain under-selected and noisy. At the same time, speed takes precedence over realism in most interactive applications. However, the desire to improve the quality of graphics prompted the development of various fast approximations for realistic lighting. This paper presents a combined method for visualizing refraction of light and caustics using reverse integration for illumination and direct integration for viewing rays. An approach is used for simultaneous propagation of light and for tracking rays in volume and, therefore, it does not require storing data of an intermediate volume of illumination. In the implementation of the method, the distance between the light planes is set to one voxel, which provides at least one sample per voxel for all orientations. The method does not use preliminary calculations; all rendering parameters can be changed interactively. As a result, using the proposed method, it is possible to create plausible approximations of complex phenomena such as refractions and caustics. The effect of refraction on the shadow is shown. Complex light patterns are demonstrated due to the curved geometry of the objects. The visualization results show the importance of refraction for the appearance of transparent objects. For example, distortions caused by refraction and refraction at the interface between media. The difference in refractive indices between individual media causes a complex interaction between light and shadow areas. It is shown how refraction and caustics improve the visualization of functionally defined objects by providing additional information about shape and location.

A Non-Contact Measurement of Animal Body Size Based on Structured Light

To improve the accuracy of non-contact measurements of animal body size and reduce costs, a new monocular camera scanning equipment based on structured light was built with a matched point cloud generation algorithm. Firstly, using the structured light 3D measurement model, the camera intrinsic matrix and extrinsic matrix could be calculated. Secondly, the least square method and the improved segment–facet intersection method were used to implement and optimize the calibration of the light plane. Then, a new algorithm was proposed to extract gray- centers as well as a denoising and matching algorithm, both of which alleviate the astigmatism of light on animal fur and the distortion or fracture of light stripes caused by the irregular shape of an animal’s body. Thirdly, the point cloud was generated via the line–plane intersection method from which animal body sizes could be measured. Finally, an experiment on live animals such as rabbits and animal specimens such as fox and the goat was conducted in order to compare our equipment with a depth camera and a 3D scanner. The result shows that the error of our equipment is approximately 5%, which is much smaller than the error of the other two pieces of equipment. This equipment provides a practicable option for measuring animal body size.

From Constantinople to the South Caucasus: Deciphering the urban landscape in John Dos Passos’s travel memoir “Orient Express”

This article examines a highly-regarded but little-studied work of the major American novelist John Dos Passos, the travel memoir Orient Express (1927), the account of a 1922 journey from Constantinople, through the South Caucasus and through Iran and Iraq to the Levant. Situating Orient Express within the development of Dos Passos’s distinctive brand of experimental, modernist prose culminating in the U.S.A. trilogy (1930–1937), attention is drawn to the visual and auditory landscapes of the text. Dos Passos’s use of various modernist devices in his portrayal of Near Eastern cities — including the use of overlapping perspectives, interacting planes of light and color, the observer-in-motion and the superimposition of real and imagined city landscapes — approach what has been termed the “proto-cubist” or “proto-expressionist” effect typical of his urban American novels. Orient Express is also characterized by its unique auditory landscape, a patchwork of overheard speech which prefigures Dos Passos’s mature conception of a fragmentary, “objective” art in which authorial agency consists primarily in ordering various strands of external discourse. These verbal and material planes, image and history, intersect in a crucial meditation on material artifacts abandoned by their owners in the wake of the Red Army’s invasion of Georgia, which reflects a conception of the “the writer’s vital role in opposing the dehumanizing impact of mechanization,” and provides important context for the much remarked-upon transition in Dos Passos’s political views toward the end of the 1930s.

High accuracy calibration method for multi-line structured light three-dimensional scanning measurement system based on grating diffraction.

Multi-line structured light three-dimensional (3D) scanning measurement system enables to obtain the richer 3D profile data of the object simultaneously during one frame, ensuring high accuracy while structured light is deformed for the modulation by the object. Nevertheless, current calibration methods cannot fully take advantage of its high precision. In this paper, a fast and high-accuracy 3D measurement system based on multi-line lasers with a spatially precise structure via integrating a diffraction grating was proposed. This helps achieve precise calibration results of the light planes by introducing spatial constraint relations of the diffractive light, thus improving measurement accuracy. The operating principle and the workflow of the proposed system were described in detail. The measurement accuracy of the developed prototype was verified through contrastive experiments. At a working distance of 400 mm, the results show that the root mean square error (RMSE) of the proposed system is 0.083 mm, which is improved by 37.6% compared to the traditional calibration method of light planes for the ranging system. The system utilizing a grating that facilitates the integration of the device has great application value.

Development of a novel multi-line laser triangulation scanning system based on the rotary diffraction grating

The laser triangulation scanning system (LTSS) is widely employed in three-dimensional (3D) measurement fields owing to its high measurement accuracy. However, due to the limitations of the exploited motion, the traditional LTSS fails to be satisfactory for certain precise and efficient industrial applications. In this paper, a new multi-line laser triangulation scanning system (MLTSS) via integrating a rotary diffraction grating was proposed to address this problem. The image sequence of the divergent laser lines with variable angles on the object can be captured as the grating rotates. This enables to obtain the multiple profiles simultaneously during one frame. A novel method to distinguish laser lines in a single frame which enhances the measurement range was described. The measurement principle and workflow of the proposed system are explained in detail. The calibration algorithm of light planes of the proposed system utilizing the equivalent grating equation is simplified compared to the traditional algorithm. The developed setup and the measured object remain stationary throughout the whole scanning, which relieves the mechanical error caused by the motion. Moreover, the utilized grating facilitates to miniaturize the device. The experiments demonstrate the validity of the proposed system.

Facilitating light utilization and electron transfer of TiO2 nanotube arrays for catalyzing photoelectrochemical water reduction via acid etching and copper doping

Photoelectrochemical catalytic capability mainly relies on light absorption and charge transfer efficiency. TiO2 nanotube array (TNA) having suitable band edges and one-dimensional hollow structure is regarded as one of efficient photoelectrocatalysts toward water reduction. In this study, two strategies are firstly applied to modify TNA as the photocatalyst of water reduction. Ti foils are etched by acid to produce multiple light reflections planes for improving light absorption, and Cu is doped in TNA to enhance charge transfer efficiency. The optimal Cu-doped TNA electrode on the acid-etched Ti foil presents a much smaller overpotential of 91 mV at 10 mA/cm2 compared with that of the undoped TNA (524 mV). A smaller Tafel slope of 134 mV/dec is obtained for the optimal Cu-doped TNA electrode than that of the undoped TNA (167 mV/dec). After measuring the photoelectrochemical performance for 1000 cycles, overpotential and charge-transfer resistance of modified TNA are largely reduced owing to activation. Current retention of 96.7% is achieved after continuously illuminating for 10 h. Highly improved photoelectrochemical catalytic ability of TNA modified by acid etching and Cu doping provides new pages for material modifications on substrate and active material.