Virtual Plane Research Articles

Theoretical Aspects of Remote Learning in Grades I–III of the Primary School

Early childhood education is an essential stage in the life of every child. Thanks to participation in lessons and school life, the child not only gains knowledge and various skills, but also shapes his personality, establishes bonds, and learns how to function in a social group. At the beginning of March 2020, the current order, also in the field of education, was disrupted by the outbreak of the Covid-19 pandemic. By decision of the state authorities, schools and many other public facilities were closed. Education has changed its current form by moving completely on the virtual plane, which has never happened before. The extremely fast turn of events caused huge chaos in both the pedagogical environment and among parents and their children. This has become a contribution to the theoretical and research considerations of many people.

Image Dynamics-Based Visual Servo Control for Unmanned Aerial Manipulatorl With a Virtual Camera

This article proposes a visual servo control method based on image dynamics for an unmanned aerial manipulator (UAM) combining an unmanned aerial vehicle (UAV) with a multidegree-of-freedom onboard manipulator. First, taking into account the dynamic characteristics of the coupled UAM, the dynamic model of the coupled system is derived. Then, based on the perspective projection model, the appropriate image features are defined on the virtual image plane to obtain decoupled image feature dynamics. Combining image features dynamics and UAM dynamics, the position and attitude controller of the UAM flying platform with the center of gravity compensation is derived. Furthermore, the image feature motion is further applied to the positioning control of the end-effector of the onboard manipulator. In addition, the UAM motion distribution strategy is designed to coordinate the movement between the UAM flying platform and the onboard manipulator. The simulation results illustrate the performance of the proposed visual servo control based on image dynamics. As a result, the trajectories of the feature points are smooth in the real image plane, which means the UAM movement is stable. Finally, the experimental results in an outdoor environment verify the practicability and effectiveness of the proposed visual servo control method for autonomous operations. The proposed control method manages the UAM from an unknown initial position to the desired position, which can be applied to various types of aerial operations missions such as object transmission.

Image-based finite-time visual servoing of a quadrotor for tracking a moving target

This paper proposes an image-based visual servoing control method for a moving target of a quadrotor UAV (QUAV). Firstly, the dynamic image model with moving target parameters is established based on the image moment features in the virtual camera plane. For the unpredictability of the moving target in space, we use a high-order differentiator to estimate the state parameters of the moving target. In order to solve the problem of image depth information caused by a monocular camera, we derive a nonlinear finite-time linear velocity observer from the virtual image plane, which can not only estimate the linear velocity information of QUAV but also avoid the measurement of image depth. Based on the above information, we design the global finite-time controller and use Lyapunov theory to prove the finite-time stability of the system. Finally, the numerical simulations verify the convergence of the proposed control scheme, and the ROS gazebo simulations demonstrate the improved performance of the proposed control scheme in tracking error.

Research on a Visual Servoing Control Method Based on Perspective Transformation under Spatial Constraint

Visual servoing has been widely employed in robotic control to increase the flexibility and precision of a robotic arm. When the end-effector of the robotic arm needs to be moved to a spatial point without a coordinate, the conventional visual servoing control method has difficulty performing the task. The present work describes space constraint challenges in a visual servoing system by introducing an assembly node and then presents a two-stage visual servoing control approach based on perspective transformation. A virtual image plane is constructed using a calibration-derived homography matrix. The assembly node, as well as other objects, are projected into the plane after that. Second, the controller drives the robotic arm by tracking the projections in the virtual image plane and adjusting the position and attitude of the workpiece accordingly. Three simple image features are combined into a composite image feature, and an active disturbance rejection controller (ADRC) is established to improve the robotic arm’s motion sensitivity. Real-time simulations and experiments employing a robotic vision system with an eye-to-hand configuration are used to validate the effectiveness of the presented method. The results show that the robotic arm can move the workpiece to the desired position without using coordinates.

Reconstruction and analysis of a non-stationary sound field in a uniformly flow medium

A multistep time domain plane wave superposition method (M-TPWM) is expanded into a new environment that the medium is fluid, and an M-TPWM with flow medium (FM-TPWM) is proposed to reconstruct the non-stationary sound field in a uniformly flow medium. In the FM-TPWM, two situations that the flow directions of the medium are parallel to and perpendicular to the hologram plane are researched. The time-varying pressures on the hologram plane in these two situations are expressed as a superposition of time convolutions between the pressure time-wavenumber spectra of a virtual source plane and the corresponding new time domain propagation kernel derived in the flow medium. Subsequently, the discrete solving equations in the parallel and perpendicular situations at one time are established. The pressure time-wavenumber spectra at only this time can be solved by once solving inverse calculation. Then, these discrete solving equations in the flow medium at several times are combined for forming the larger solving matrix equations in the parallel and perpendicular situations, and by once multistep calculation, the pressure spectra at these times are acquired concurrently. Consequently, the time-varying pressures on the reconstruction plane in the flow medium are calculated by the corresponding acquired pressure time-wavenumber spectra. Numerical simulations with parallel and perpendicular situations are applied to examine the performance of the proposed FM-TPWM, in which two monopole sources in the flow medium are used to engender the non-stationary sound field. The simulation results prove that the proposed FM-TPWM can reconstruct the non-stationary sound field very well when the flow directions of the medium are parallel to and perpendicular to the hologram plane, respectively. Besides, several meaningful parameters are discussed in detail to prove the adaptability and robustness of the proposed FM-TPWM in the flow medium, and its reconstruction advantages are protruded in comparison to the real-time nearfield acoustic holography with the flow medium.

Explosive dispersal of particles in high speed environments

In this paper, we present the results of the explosive dispersal of particles in high-speed environments. We carry out Euler–Lagrange numerical simulations of a source at quiescent ambient conditions as well as moving at Mach numbers of 3 and 6. Particle volume fractions of 0%, 1%, and 4.5% are presented. The detonation profile is computed with the Jones–Wilkins–Lee equation of state using a reactive burn model. Non-static cases provide a framework to consider the effect of a bow shock and pre-existing high-speed flow conditions on the dispersal process. We also compute averages of both static and dynamic pressures, as well as impulse density histories on virtual probe planes to characterize the momentum of the flow and particles that would deposit on a target. Results suggest that the presence of the particles can have a substantial effect on the pressure average of the virtual target planes.

Autonomous ship deck landing of a quadrotor UAV using feed-forward image-based visual servoing

Autonomous takeoff and landing are crucial for unmanned aerial vehicles (UAVs) to perform various missions automatically. However, navigation sensors with low accuracy such as global positioning system (GPS) are limited in autonomous takeoff and landing for marine applications when ships are moving fast and oscillating by sea waves. In this study, an image-based visual servoing (IBVS) technique, which was originally used to land a UAV on a static target, is extended for a moving target. In particular, the ship velocity is estimated and used as a feed-forward term in the IBVS controller. To accurately estimate the velocity of the ship, velocity data from the GPS on the ship, image information obtained from the camera in the UAV, and dynamic model of the ship are combined using the Kalman filter framework. Besides, considering the under-actuated nature of the UAV and oscillation of the ship, a virtual plane concept, adaptive IBVS gain and feature shape compensation are introduced. Lastly, to apply the IBVS controller to the moving ship deck landing, a robust and safe autonomous landing procedure, starting from the approach to the touchdown phase, is also developed. The proposed autonomous landing system is validated via simulations and various real-world flight experiments simulating situations in which the ship is moving fast and oscillated by sea waves. In the flight experiments, the UAV lands successfully on the landing pad with the average touchdown error of 0.2m while the ship is oscillating at the Sea State 4 and is moving faster than 5m/s.

Design and Implementation of Print Advertisement Based on Computer Image Interactive Virtualization

This study aimed to further enhance and enrich users’ visual experience, provide users with a more infectious image sense, and further promote the development of multidimensional, virtualized, and interactive graphic advertising design applications. This study presents a design idea of print advertisement based on computer image interactive virtual technology. Based on the in-depth analysis of the multidimensional expression of plane image interactive virtualization, this idea carries out interactive virtual design with the help of interactive virtual image segmentation algorithm and plane advertising image element optimization technology. Through the test of image interactive edge extraction function on MATLAB platform, the simulation results show that the edge width of single side extraction results with different gray levels of the same width and different widths of the same gray level are 9 pixels, the gray values are 5a0, 110, and 200, respectively, and the edge width corresponds to 3, 9, and 15 pixels, respectively. The results show that the system can effectively enhance the image definition and obtain better print advertising design effect.

Seamless holographic image generation for a multi-vision system

This paper investigates the optical seamlessness of a holographic multi-vision display. The purpose of the multi-vision approach is to scale up the resolution of a holographic display without requiring a single extremely high-resolution spatial light modulator. Optical experiments reveal that a holographic multi-vision system with 16M pixel resolution successfully generates a seamless virtual reference plane with the essential optical characteristics of a holographic display, such as the accommodation effect and binocular parallax. It is realized from a matrix of eight (42) high-resolution transmission-type liquid crystal displays. Theoretical analysis and numerical simulations are presented for the proposed seamless holographic multi-vision system.

Virtual camera-based visual servoing for rotorcraft using monocular camera and gyroscopic feedback

In this paper, an image-based visual servoing (IBVS) control strategy with a virtual camera frame is proposed for multirotor vehicles. Compared to previous works, the proposed IBVS controller requires minimal sensors in the position loop: a monocular camera and gyroscope. To achieve this, the visual feature projected onto the virtual image plane is associated with the plane’s normal instead of relying on an additional attitude estimator and prior knowledge of the plane’s inclination. Furthermore, we show that the ratio velocity, when scaled by the image moment, exhibits a similar dynamics to the linear velocity. The finding allows the quantity to be recovered and used for control with a monocular camera without other metric cues. To provide feedback for the controller, an Extended Kalman filter for estimating the ratio velocity, target plane’s inclination, and relative rotation between the current and reference camera frame is developed using only monocular vision and gyroscopic measurements. To validate the proposed controller and estimation strategy, both simulation and real-world flight experiments were carried out. The quadrotor smoothly and robustly tracked both dynamic horizontal and static inclined targets, without prior knowledge of the target’s inclination. Overall, the proposed regime offers a lightweight and robust alternative IBVS solution for rotorcraft.

Vision occlusion solution for line-structured light measurement system based on a plane mirror

To solve the problem of the measurement information loss caused by occlusion of the field of view in line-structured light measurement, a vision occlusion solution of the line-structured light measurement system based on a plane mirror is proposed in this work. In the system, a symmetrical structure between real and virtual images was created by the mirror. A checkerboard with a light stripe and its mirror image were captured by the camera in an image. The centers of the light stripe and its mirror image were corrected by the vanishing point constraint, and a calibration method of the free plane target was used to calibrate the real and virtual light planes. The real and virtual point clouds of the object were obtained by scanning with a linear guide. According to the ideal reflection model of the mirror, the real and virtual point clouds of the object were transformed into a common coordinate system, and an iterative closest point (ICP) algorithm was used to realize fine registration. As a result, the occluded parts can be compensated for each other. Compared with a standard ball, the mean/maximum absolute error of the measurement was 0.2553/0.3276 mm. The experimental results revealed that the proposed method can obtain the complete surface of the object, thus effectively solving the occlusion problem in the line-structured light measurement, and reducing the loss of the measurement information, which can meet the industrial measurement requirements.

B-spline surface based 3D reconstruction method for deflectometry.

In the field of optical three-dimension (3-D) measurement, reconstruction usually is completed by the integration of a two-dimensional (2-D) gradient data set. Position and posture of camera and shape of the surface under test determine the location of gradient data which usually is on quadrilateral grids. This paper proposes a B-spline surface-based 3D reconstruction method for deflectometry, which reconstructs the surface under test with its 2-D gradient data set. The 2-D gradient data set consists of gradient data and the 2-D location of the gradient data in the camera coordinate system. The 2-D gradient data set is first transferred to the cameras' virtual image plane, so it locates on rectangular grids. Then, based on the properties of the B-spline basis function and characteristics of the camera, linear equations are derived to solve control points along the virtual image plane. The solved control points reconstruct the surface under test in the camera coordinate system. The property of the B-spline basis function determines the relationship between the depth of the surface and its derivative. The characteristic of the camera determines the relationship between the depth of the surface and the 2-D location of the gradient data. Meanwhile, the accuracy of the 2-D location can also be improved by the linear equations. Finally, simulated and actual experiments show that the proposed method is accurate and efficient at reconstructing surfaces in deflectometry.

Design of a dual focal-plane near-eye display using diffractive waveguides and multiple lenses.

We propose a method to construct a compact dual focal-plane optical see-through near-eye display using diffractive waveguides and multiple lenses. A virtual image from a display device is projected into a three-grating waveguide using an objective lens, and a virtual image can be shown at a far distance with an extended eye box. One negative lens is employed to reduce the focus distance of the virtual image, and a corresponding positive lens is used to compensate for the distortion and accommodation errors. Thus, not only can a virtual image with a near distance be achieved, but also a virtual plane with a further distance can be generated by introducing another projection module and waveguide. Only two waveguides and two pieces of lenses are used in front of one eye to obtain a lightweight outlook. To verify the proposed method, a proof-of-concept prototype was developed to provide vivid virtual images at different depths in front of the human eye.

Field-of-view correction in a VR HMD display with varifocal optics

Nowadays, we observe a progressive increase amount of virtual technologies application. VR devices, i.e. HMDs, are still struggling with the VAC. It is possible to “implement” the accommodation mechanism in HMDs using a varifocal system. By using focus tuneable lenses, we achieve high speed and smoothness of displacement of the virtual image plane. This solution involves also unfavourable changes of geometrical parameters of the projected image i.e. change in magnification. This can be solved by software modification parameters of the virtual camera. In this paper, the developed construction of varifocal HMD is presented, including the method of maintaining the constancy magnification. Full Text: PDF ReferencesY-J. Wang , Y-H. Lin, "Liquid crystal technology for vergenceaccommodation conflicts in augmented reality and virtual reality systems: a review", Liq. Cryst. Rev. 9. 35 (2021). CrossRef P.P. Monticone, M. Menozzi, M. Schlup, "Instrument for high-speed recording of accommodation of the human eye", Biomed. Tech. 55: 83 (2010). CrossRef G. Kramida, "Resolving the vergence-accommodation confict in headmounted displays", IEEE Trans. Vis. Comput. Graph. 22, 1912 (2016). CrossRef S. Shiwa, K. Omura, and F. Kishino, "Proposal for a 3-D display with accommodative compensation: 3DDAC," J. Soc. Inf. Disp. 4, 255 (1996). CrossRef K. Rathinavel, G. Wetzstein, H. Fuchs, "Varifocal Occlusion-Capable Optical See-through Augmented Reality Display based on Focus-tunable Optics," IEEE Trans. Vis. Comput. Graph. 25, 3125 (2019). CrossRef

Application of an artificial neural network in the recognition of geometric figures

The objective was to implement an artificial neural network to improve the recognition of geometric figures that later allow making estimates about shapes in a real context to create virtual planes. A Matlab program was developed to create the neural network and two knowledge bases containing fifteen different geometric figures that were developed for the training stage and for the recognition stage. The results of the training phase were carried out in three processes, obtaining a percentage of 11.35%, 3.55%, and 2% error margin respectively, later came the recognition stage with three processes, obtaining 40%, 100%, and 100% figures recognized respectively. It is concluded that the implemented neural network performed the recognition of fifteen geometric figures correctly (100%), requiring three training processes and three recognition processes to verify their learning.
 Keywords: Image recognition, Machine learning, artificial neural networks, artificial intelligence.

GPU-Accelerated Target Strength Prediction Based on Multiresolution Shooting and Bouncing Ray Method

The application of the traditional planar acoustics method is limited due to the low accuracy when computing the echo characteristics of underwater targets. Based on the concept of the shooting and bouncing ray which considers multiple reflections on the basic of the geometrics optics principle, this paper presents a more efficient GPU-accelerated multiresolution grid algorithm in the shooting and bouncing ray method (SBR) to quickly predict the target strength value of complex underwater targets. The procedure of the virtual aperture plane generation, ray tracing, scattered sound field integral and subdividing the divergent ray tubes are all implemented on the GPU. Particularly, stackless KD-tree traversal is adopted to effectively improve the ray-tracing efficiency. Experiments on the rigid sphere, cylinder and corner reflector model verify the accuracy of GPU-based multiresolution SBR. Besides, the GPU-based SBR is more than 750 times faster than the CPU version because of its tremendous computing capability. Further, the proposed accelerated GPU-based multiresolution SBR improves runtime performance at least 2.4 times that of the single resolution GPU-based SBR.

Nonlinear Instability Behavior and Buckling of Shallow Arches Under Gradient Thermo-Mechanical Loads

This paper investigates the nonlinear behavior and buckling of shallow arches under gradient thermal and mechanical loading. The gradient temperature varies continuously along the thickness of the cross section of the arch but uniformly distributes over the entire length of the arch. The principle of virtual work and mid-plane plane formulations are employed to derive analytical solutions for the structural responses, internal force and critical buckling loads of the arch. Subsequently, the phenomenon of the buckling mode switching are also identified and discussed. It is found that the fixed arch under gradient thermo-mechanical loading can buckle in a symmetric instability mode or an anti-symmetric instability mode, namely limit point buckling or bifurcation buckling, which depend on its geometric parameter and the gradient temperature. The effects of the gradient temperature change on the radial displacement, axial displacement, axial compressive force and bending moment as well as critical buckling loads of the arch are investigated through parametric studies comprehensively.

Analysis of popliteal artery location for high tibial and distal tuberosity osteotomy using contrast-enhanced computed tomography

BackgroundOur objective was to evaluate the location of popliteal artery (PA) in osteotomy planes during high tibial osteotomy (HTO) and to determine a safer angle for screw drilling to the tibial tuberosity during distal tuberosity osteotomy (DTO).MethodsTwenty knees in 20 patients who underwent contrast-enhanced computed tomography for cardiovascular diseases were examined. Osteotomy planes for open-wedge HTO (OWHTO) and hybrid closed-wedge HTO (hybrid CWHTO) were created using three-dimensional bone models. The distance from the posterior cortex of the tibia to the PA (dPC-PA) in the osteotomy planes was measured in the virtual osteotomy planes. The dangerous point (Point D1) was defined as the point 17.5 mm away from PA, setting the working length of the bone saw as 35 mm. The distance between the most medial point of the tibial cortex (Point M) and Point D1 in OWHTO and the most lateral point (Point L) and Point D1 in hybrid CWHTO were examined (dM-D1 and dL-D1, respectively). The location of Point D1 to the osteotomy line (%D1) was expressed as percentage, setting the start and end of the osteotomy line as 0% and 100%, respectively. To determine the safe angle for screw drilling in DTO, the angle between the line tangential to the medial cortex of the tibia and that passing through the center of the tibial tuberosity and PA were measured.ResultsIn OWHTO and hybrid CWHTO, the mean dPC-PA was 10.6 mm (6.9–16.5 mm) and 10.2 mm (7.3–15.4 mm), respectively. The mean dM-D1 in OWHTO was 25.9 mm (24.6–27.2 mm) and dL-D1 in hybrid CWHTO was 5.1 mm (2.9–7.4 mm). The mean %D1 was 47.6 ± 3.7% in OWHTO and 9.3 ± 4.1% in hybrid CWHTO, respectively. The minimal angle between the two lines in DTO was 35.2°.ConclusionPAs could run within 10 mm from the posterior cortex in the osteotomy planes of HTO. Therefore, proper posterior protection is necessary when cutting posterior cortex. An angle of less than 35° against the medial cortex line would be safe for screw fixation to avoid vascular injury in DTO.

Kalman-filter-based time-domain plane wave superposition method for reconstructing an instantaneous sound field

A Kalman-filter-based time-domain plane wave superposition method (KF-TDPWSM) is proposed for reconstructing the instantaneous sound field generated by a source. In the KF-TDPWSM, a discrete state formulation is first acquired using the superposition formula of time-varying pressure on a hologram plane, which forms a multiple-input and multiple-output acoustical system. Then, an eigensystem realization algorithm is implemented to obtain the minimum realization of this system. The process and measurement equations of the KF-TDPWSM are established by combining the equation of the first-order smoothness condition with the minimum realization. Finally, the forward iteration calculation of the Kalman filter is used to estimate the state vector, including the pressure time–wavenumber spectra on a virtual source plane. The spectra estimated at all times are employed to calculate the time-varying pressure on a reconstruction plane. The KF-TDPWSM utilizes a forward iteration calculation and does not use the inverse calculation with the time-marching characteristic to improve the reconstruction stability of the instantaneous sound field. A numerical simulation is designed to investigate the reconstruction performance of the KF-TDPWSM. Simulation results confirm that the KF-TDPWSM effectively reconstructs the instantaneous sound field of a source in the time and space domains. The effects of certain parameters of the KF-TDPWSM are examined through simulations, and it is shown that its reconstruction accuracy is superior to that of the time-domain plane wave superposition method. An experiment is conducted to further validate the KF-TDPWSM.

Computer simulation to predict size distribution of track-etched nanopores

Track-etched nanoporous membranes prepared by swift heavy ion irradiation are promising for separation processes such as water purification. However, one drawback is that multiple pores are undesirably formed by pore overlapping to reduce separation performance. The techniques for predicting the size and amount of multiple pores in detail are still underdeveloped, which hinders the precise membrane design. In this study, a computer simulation program was developed to predict the size distribution of the track-etched pores. The program generates a number of single pores on the virtual grid plane to simulate random ion bombardment, finds multiple pores containing several single pores, and determines the multiple pore size by counting the inside grid points. All the multiple pores are categorized into different size classes, and the areal percentage occupied by the pores belonging to each size class is estimated. The simulation algorithm and the results of a model case simulation were described.