Calibration Method for Line-Structured Light Three-Dimensional Measurements Based on a Single Circular Target

Single circular targets are widely used as calibration objects during line-structured light three-dimensional (3D) measurements because they are versatile and easy to manufacture. This paper proposes a new calibration method for line-structured light 3D measurements based on a single circular target. First, the target is placed in several positions and illuminated by a light beam emitted from a laser projector. A camera captures the resulting images and extracts an elliptic fitting profile of the target and the laser stripe. Second, an elliptical cone equation defined by the elliptic fitting profile and optical center of the camera is established based on the projective geometry. By combining the obtained elliptical cone and the known diameter of the circular target, two possible positions and orientations of the circular target are determined and two groups of 3D intersection points between the light plane and the circular target are identified. Finally, the correct group of 3D intersection points is filtered and the light plane is progressively fitted. The accuracy and effectiveness of the proposed method are verified both theoretically and experimentally. The obtained results indicate that a calibration accuracy of 0.05 mm can be achieved for an 80 mm × 80 mm planar target.

Characterization of the Propagation Route of Light Passing Through Convex Lens

Existing optical theory states that the light directed to the optical center of the convex lens will travel in a straight line. Does the theory hold? If this is true, then why the images formed by the camera lens tends to be distorted? To answer the question, this paper studied the propagation mode of light passing through convex lens. Specifically, assuming the propagation medium on both sides of convex lens is homogeneous, we propose an angular affine transformation (AAT) theory. Based on the proposed theory, we first derive the refractive index of convex lens as well as the method of calculating the normal direction of each point within the radius of convex lens radius and then derive the refraction direction of each point within the radius of convex lens, thus completely characterizing the path diagram of light directed to the optical center. The correctness of the proposed theory has been verified using two sets of experiments: characterization of the route of light passing through the convex lens as well as camera imaging experiment. From the results, it can be concluded that the light directed to the optical center of convex lens does not travel in a straight line, but in a refraction line.

Visual Tracking with Object Center Displacement and CenterNet

Modern artificial intelligence systems have revolutionized approaches to scientific and technological challenges in a variety of fields, thus remarkable improvements in the quality of state-of-the-art computer vision and other techniques are observed; object tracking in video frames is a vital field of research that provides information about objects and their trajectories. This paper presents an object tracking method basing on optical flow generated between frames and a ConvNet method. Initially, optical center displacement is employed to detect possible the bounding box center of the tracked object. Then, CenterNet is used for object position correction. Given the initial set of points (i.e., bounding box) in first frame, the tracker tries to follow the motion of center of these points by looking at its direction of change in calculated optical flow with next frame, a correction mechanism takes place and waits for motions that surpass a correction threshold to launch position corrections.

Three-dimensional mapping of the optical centers in the bulk of natural diamond by photoluminescent spectroscopy

Optically active defects in natural diamonds form specific spectral bands in the optical absorption and luminescence spectra and are called optical centers. Optical centers in the visible spectral range and their corresponding defects are called color centers. Spectral absorption and luminescence bands usually occupy several tens of nanometers in the spectral range and often have a complex structure. This spectral structure is unique to each optical center. The stationary broadband UV-MIR characterization of the set of optically active defects in the bulk of natural diamond with a widely varying concentration of impurities was carried out in this work. Comparison of the initial and modified impurity-defect structures of near-surface diamond layers was carried out by the method of cathodoluminescence and cathodoluminescence topography.

Development of 3D environmental laser scanner using pinhole projection

Three-dimensional (3D) information of capturing and reconstructing an object existing in its environment is a big challenge. In this work, we discuss the 3D laser scanning techniques, which can obtain a high density of data points by an accurate and fast method. This work considers the previous developments in this area to propose a developed cost-effective system based on pinhole projection concept and commercial hardware components taking into account the current achieved accuracy. A laser line auto-scanning system was designed to perform close-range 3D reconstructions for home/office objects with high accuracy and resolution. The system changes the laser plane direction with a microcontroller to perform automatic scanning and obtain continuous laser strips for objects’ 3D reconstruction. The system parameters were calibrated with Matlab’s built-in camera calibration toolbox to find camera focal length and optical center constraints. The pinhole projection equation was defined to optimize the prototype rotating axis equation. The developed 3D environmental laser scanner with pinhole projection proved the system’s effectiveness on close-range stationary objects with high resolution and accuracy with a measurement error in the range (0.05–0.25) mm. The 3D point cloud processing of the Matlab computer vision toolbox has been employed to show the 3D object reconstruction and to perform the camera calibration, which improves efficiency and highly simplifies the calibration method. The calibration error is the main error source in the measurements, and the errors of the actual measurement are found to be influenced by several environmental parameters. The presented platform can be equipped with a system of lower power consumption, and compact smaller size

Detailed Calibration of the Off-Axis Optical Characteristics for the X-Ray Telescope onboard Hinode

<p>The X-Ray Telescope (XRT) onboard the Hinode satellite has a specially designed Wolter type grazing-incidence (GI) optics with a paraboloid-hyperboloid mirror assembly to measure the solar coronal plasma of temperatures up to 10 MK with a resolution of about one arc sec. One of the main purposes of this scientific mission is to investigate the detailed mechanism of energy transfer processes from the photosphere to the upper coronal region leading to its heating and the solar wind acceleration. An astronomical telescope is in general designed such that the best-focused image of an object is achieved at or very close to the optical axis, and inevitably the optical performance deteriorates away from the on-axis position. The Sun is, however, a large astronomical object and thus targets near the limb of full-disk images are placed at the outskirt of the field of view. The design of a solar telescope should thus consider the uniformity of imaging quality over a wide FOV, and it is particularly so for X-ray telescopes whose targets can be in the corona high above the limb.</p><p> </p><p>We will explain in this presentation the importance of detailed calibration of the off-axis optical characteristics for Hinode/XRT. It have been revealed that the scattered light caused by the GI mirror surface has a power-law distribution and shows an energy dependence. We will also introduce the basic scheme of how the level of scattering wing is determined and connected to the core from the analysis of highly saturated in-flight data. Vignetting is another important optical characteristics for describing the telescope's performance, which reflects the ability to collect incoming light at different locations and photon energies. We have evaluated the vignetting effect in Hinode/XRT by analyzing the ground experimental data and found that the degree of vignetting varies linearly from the optical center and its pattern shows an energy dependence. Many interesting results on the calibration of Hinode/XRT optical characteristics will be introduced and discussed thoroughly. </p>

Profile of cytokines in aqueous humor and trabecular meshwork cell culture in patients with pseudoexfoliation glaucoma

Glaucoma is one of the leading causes of irreversible blindness worldwide, being an age-related disease. Its pathogenesis still is not fully understood. A particular interest is attracted to evaluation of the cytokine concentrations in the trabecular meshwork cell culture, and in the aqueous humor (AH) taken from the same patient, since such data may allow to describe more completely the glaucomatous trabecular changes and to clarify the mechanisms of intercellular interactions in pseudoexfoliative (PEX) glaucoma. The purpose of this study was a comparative analysis of cytokine contents in AH and in trabecular tissue (TT) supernatants in the patients with PEX glaucoma. The study included 23 eyes of patients with PEX glaucoma. The material studied was AH and supernatant of TT cell culture. The cytokine concentration was measured using a flow cytofluorimeter FacsCantoII (BD, USA) using the CBA method. SPSS version 19 software (IBM, USA) was used for the statistical data processing. Concentrations of cytokines (TNFα, IFNγ, IL-1β, IL-6, IL-8, IL- 10, VEGF, GM-CSF) were determined in AH and in the TT supernatant for each of the patients with PEX glaucoma. Only IL-6 and VEGF concentrations in AH were higher than those in the TT supernatant in patients with PEX glaucoma. The IL-6 concentration positively correlated with the VEGF and IL-8 concentrations in the TT supernatant. Correlations between other cytokines in the TT supernatant and AH were also identified and analyzed. Multiple regression analysis revealed that the duration of glaucoma and the IFNγ and TNFα concentrations in AH may have a significant influence on the corneal endothelial cells, being associated with density reduction in patients with PEX glaucoma. The correlation analysis did not reveal any links between other clinical data (corneal thickness in the optical center, IOP level, age) and the cytokine concentrations in the studied tissues. The obtained results suggest that only simultaneous analysis of the cytokine concentrations in the TT supernatant and AH taken from the same patient may provide a more complete description of the cytokine imbalance and pathological processes occurring in the trabecular meshwork in PEX glaucoma patients. It has been shown that the changing cytokine ratios observed in PEX glaucoma may be associated with development of uniform structural and functional changes in all tissues of the anterior eye segment.

A Model of Diameter Measurement Based on the Machine Vision

If the shaft diameter can be measured in-situ during the finishing process, the closed-loop control of the shaft diameter processing process can be realized and the machining accuracy can be improved. Present work studies the measurement of shaft diameter with the structured light system composed of a laser linear light source and a camera. The shaft is a kind of part with rotationally symmetric structure. When the linear structured light irradiates the surface of the shaft, a light stripe will be formed, and the light stripe is a part of the ellipse. Therefore, the in-situ measurement of the shaft diameter can be realized by the light stripe and the rotational symmetry of the shaft. The measurement model of shaft diameter is established by the ellipse formed by the intersection of the light plane and the measured shaft surface. Firstly, in the camera coordinate system, normal vector of the light plane and the coordinates of the ellipse center are obtained by the calibration; then, the equation of oblique elliptic cone is established by taking the ellipse as the bottom and the optical center of the camera as the top. Next, the measurement model of shaft diameter is obtained by the established oblique elliptic cone equation and theoretical image plane equation. Finally, the accuracy of the measurement model of shaft diameter is tested by the checkerboard calibration plate and a lathe. The test results show that the measurement model of shaft diameter is correct, and when the shaft diameter is 36.162mm, the speed is 1250r/min, the maximum average measurement error is 0.019mm. The measurement accuracy meets the engineering requirement.