Three-dimensional(3D)parametric measurements of individual gravels in the Gobi region using point cloud technique

Gobi spans a large area of China,surpassing the combined expanse of mobile dunes and semi-fixed dunes.Its presence significantly influences the movement of sand and dust.However,the complex origins and diverse materials constituting the Gobi result in notable differences in saltation processes across various Gobi surfaces.It is challenging to describe these processes according to a uniform morphology.Therefore,it becomes imperative to articulate surface characteristics through parameters such as the three-dimensional(3D)size and shape of gravel.Collecting morphology information for Gobi gravels is essential for studying its genesis and sand saltation.To enhance the efficiency and information yield of gravel parameter measurements,this study conducted field experiments in the Gobi region across Dunhuang City,Guazhou County,and Yumen City(administrated by Jiuquan City),Gansu Province,China in March 2023.A research framework and methodology for measuring 3D parameters of gravel using point cloud were developed,alongside improved calculation formulas for 3D parameters including gravel grain size,volume,flatness,roundness,sphericity,and equivalent grain size.Leveraging multi-view geometry technology for 3D reconstruction allowed for establishing an optimal data acquisition scheme characterized by high point cloud reconstruction efficiency and clear quality.Additionally,the proposed methodology incorporated point cloud clustering,segmentation,and filtering techniques to isolate individual gravel point clouds.Advanced point cloud algorithms,including the Oriented Bounding Box(OBB),point cloud slicing method,and point cloud triangulation,were then deployed to calculate the 3D parameters of individual gravels.These systematic processes allow precise and detailed characterization of individual gravels.For gravel grain size and volume,the correlation coefficients between point cloud and manual measurements all exceeded 0.9000,confirming the feasibility of the proposed methodology for measuring 3D parameters of individual gravels.The proposed workflow yields accurate calculations of relevant parameters for Gobi gravels,providing essential data support for subsequent studies on Gobi environments.

Three-dimensional mixed convection stagnation-point fow past a vertical surface with second-order slip velocity

This study is concerned with the three-dimensional(3D)stagnation-point for the mixed convection flow past a vertical surface considering the first-order and secondorder velocity slips.To the authors’knowledge,this is the first study presenting this very interesting analysis.Nonlinear partial differential equations for the flow problem are transformed into nonlinear ordinary differential equations(ODEs)by using appropriate similarity transformation.These ODEs with the corresponding boundary conditions are numerically solved by utilizing the bvp4c solver in MATLAB programming language.The effects of the governing parameters on the non-dimensional velocity profiles,temperature profiles,skin friction coefficients,and the local Nusselt number are presented in detail through a series of graphs and tables.Interestingly,it is reported that the reduced skin friction coefficient decreases for the assisting flow situation and increases for the opposing flow situation.The numerical computations of the present work are compared with those from other research available in specific situations,and an excellent consensus is observed.Another exciting feature for this work is the existence of dual solutions.An important remark is that the dual solutions exist for both assisting and opposing flows.A linear stability analysis is performed showing that one solution is stable and the other solution is not stable.We notice that the mixed convection and velocity slip parameters have strong effects on the flow characteristics.These effects are depicted in graphs and discussed in this paper.The obtained results show that the first-order and second-order slip parameters have a considerable effect on the flow,as well as on the heat transfer characteristics.

A modified method of discontinuity trace mapping using three-dimensional point clouds of rock mass surfaces

This paper presents an automated method for discontinuity trace mapping using three-dimensional point clouds of rock mass surfaces.Specifically,the method consists of five steps:(1)detection of trace feature points by normal tensor voting theory,(2)co ntraction of trace feature points,(3)connection of trace feature points,(4)linearization of trace segments,and(5)connection of trace segments.A sensitivity analysis was then conducted to identify the optimal parameters of the proposed method.Three field cases,a natural rock mass outcrop and two excavated rock tunnel surfaces,were analyzed using the proposed method to evaluate its validity and efficiency.The results show that the proposed method is more efficient and accurate than the traditional trace mapping method,and the efficiency enhancement is more robust as the number of feature points increases.

Single exposure passive three-dimensional information reconstruction based on an ordinary imaging system

Existing three-dimensional(3D) imaging technologies have issues such as requiring active illumination, multiple exposures, or coding modulation. We propose a passive single 3D imaging method based on an ordinary imaging system.Using the point spread function of the imaging system to realize the non-coding measurement on the target, the full-focus images and depth information of the 3D target can be extracted from a single two-dimensional(2D) image through the compressed sensing algorithm. Simulation and experiments show that this approach can complete passive 3D imaging based on an ordinary imaging system without any coding operations. This method can achieve millimeter-level vertical resolution under single exposure conditions and has the potential for real-time dynamic 3D imaging. It improves the efficiency of 3D information detection, reduces the complexity of the imaging system, and may be of considerable value to the field of computer vision and other related applications.

The Shengli I Point Bar on the Yellow River Delta: Three-Dimensional Structures and Their Evolution

Point bars are well developed on the Yellow River delta, an~ which theShengli I point bar is the most typical. The point bar, being about 4 km in length and several tensto more than 100 meters in width, is located on the south side of the Shengli Bridge in KenliCounty, Dongying, Shandong. It is a typical fine-grained point bar with silt, which is predominant,some clay and minor plant debris and clay boulders. The Shengli I Point bar has complicated 3-Dstructures. Firstly, in a plane view, it comprises mainly eight sedimentary units, bar edge, baredge, bar platform, bar plain, bar channel, bar gully, bar pond and bar bay, developing side by sideand superimposed one by one m a complex way. Secondly, its vertical structures are very complex dueto the partial superimposition of the 8 sedimentary units. Besides hydatogenesis, very intensivewind erosion, eolian, ice and meltwater actions are also visible on the Shengli I point bar. Thecomplex form is made even more complicated because of the above co-actions.

Generation of countless embedded trumpet-shaped chaotic attractors in two opposite directions from a new three-dimensional system with no equilibrium point

A new three-dimensional （3D） continuous autonomous system with one parameter and three quadratic terms is presented firstly in this paper. Countless embedded trumpet-shaped chaotic attractors in two opposite directions are generated from the system as time goes on. The basic dynamical behaviors of the strange chaotic system are investigated. Another more complex 3D system with the same capability of generating countless embedded trumpet-shaped chaotic attractors is also put forward.

Three-dimensional nonlinear H_2/H_∞ guidance law based upon approach of solving the state feedback Nash balance point

Based upon the theory of the nonlinear quadric two-person nonzero-sum differential game,the fact that the time-limited mixed H2/H∞ control problem can be turned into the problem of solving the state feedback Nash balance point is mentioned. Upon this,a theorem about the solution of the state feedback control is given,the Lyapunov stabilization of the nonlinear system under this control is proved,too. At the same time,this solution is used to design the nonlinear H2/H∞ guidance law of the relative motion between the missile and the target in three-dimensional(3D) space. By solving two coupled Hamilton-Jacobi partial differential inequalities(HJPDI),a control with more robust stabilities and more robust performances is obtained. With different H∞ performance indexes,the correlative weighting factors of the control are analytically designed. At last,simulations under different robust performance indexes and under different initial conditions and under the cases of intercepting different maneuvering targets are carried out. All results indicate that the designed law is valid.

Three-dimensional analysis of pedicle screw channel,screw entry point and lateral surface of cervical vertebral body

Objective To explore three-dimensional relations of pedicle screw channel (PSC) ,screw entry point and lateral surface of cervical vertebral body by digital techniques. Methods CT scan images of cervical

Integration system research and development for three-dimensional laser scanning information visualization in goaf

An integration processing system of three-dimensional laser scanning information visualization in goaf was developed. It is provided with multiple functions, such as laser scanning information management for goaf, cloud data de-noising optimization, construction, display and operation of three-dimensional model, model editing, profile generation, calculation of goaf volume and roof area, Boolean calculation among models and interaction with the third party soft ware. Concerning this system with a concise interface, plentiful data input/output interfaces, it is featured with high integration, simple and convenient operations of applications. According to practice, in addition to being well-adapted, this system is favorably reliable and stable.

An unmanned ground vehicle phenotyping-based method to generate three-dimensional multispectral point clouds for deciphering spatial heterogeneity in plant traits

Fusing three-dimensional(3D)and multispectral(MS)imaging data holds promise for high-throughput and comprehensive plant phenotyping to decipher genome-to-phenome knowledge.Acquiring high-quality 3D MS point clouds(3DMPCs)of plants remains challenging because of poor 3D data quality and limited radiometric calibration methods for plants with a complex canopy structure.Here,we present a novel 3D spatial–spectral data fusion approach to collect high-quality 3DMPCs of plants by integrating the next-best-view planning for adaptive data acquisition and neural reference field(NeREF)for radiometric calibration.This approach was used to acquire 3DMPCs of perilla,tomato,and rapeseed plants with diverse plant architecture and leaf morphological features evaluated by the accuracy of chlorophyll content and equivalent water thickness(EWT)estimation.The results showed that the completeness of plant point clouds collected by this approach was improved by an average of 23.6%compared with the fixed viewpoints alone.The NeREF-based radiometric calibration with the hemispherical reference outperformed the conventional calibration method by reducing the root mean square error(RMSE)of 58.93%for extracted reflectance spectra.The RMSE for chlorophyll content and EWT predictions decreased by 21.25%and 14.13%using partial least squares regression with the generated 3DMPCs.Collectively,our study provides an effective and efficient way to collect high-quality 3DMPCs of plants under natural light conditions,which improves the accuracy and comprehensiveness of phenotyping plant morphological and physiological traits,and thus will facilitate plant biology and genetic studies as well as crop breeding.

Automatic three-dimensional reconstruction based on four-view stereo vision using checkerboard pattern

An automatic three-dimensional(3D) reconstruction method based on four-view stereo vision using checkerboard pattern is presented. Mismatches easily exist in traditional binocular stereo matching due to the repeatable or similar features of binocular images. In order to reduce the probability of mismatching and improve the measure precision, a four-camera measurement system which can add extra matching constraints and offer multiple measurements is applied in this work. Moreover, a series of different checkerboard patterns are projected onto the object to obtain dense feature points and remove mismatched points. Finally, the 3D model is generated by performing Delaunay triangulation and texture mapping on the point cloud obtained by four-view matching. This method was tested on the 3D reconstruction of a terracotta soldier sculpture and the Buddhas in the Mogao Grottoes. Their point clouds without mismatched points were obtained and less processing time was consumed in most cases relative to binocular matching. These good reconstructed models show the effectiveness of the method.

A state-of-the-art review of automated extraction of rock mass discontinuity characteristics using three-dimensional surface models

In the last two decades,significant research has been conducted in the field of automated extraction of rock mass discontinuity characteristics from three-dimensional(3D)models.This provides several methodologies for acquiring discontinuity measurements from 3D models,such as point clouds generated using laser scanning or photogrammetry.However,even with numerous automated and semiautomated methods presented in the literature,there is not one single method that can automatically characterize discontinuities accurately in a minimum of time.In this paper,we critically review all the existing methods proposed in the literature for the extraction of discontinuity characteristics such as joint sets and orientations,persistence,joint spacing,roughness and block size using point clouds,digital elevation maps,or meshes.As a result of this review,we identify the strengths and drawbacks of each method used for extracting those characteristics.We found that the approaches based on voxels and region growing are superior in extracting joint planes from 3D point clouds.Normal tensor voting with trace growth algorithm is a robust method for measuring joint trace length from 3D meshes.Spacing is estimated by calculating the perpendicular distance between joint planes.Several independent roughness indices are presented to quantify roughness from 3D surface models,but there is a need to incorporate these indices into automated methodologies.There is a lack of efficient algorithms for direct computation of block size from 3D rock mass surface models.

Methodology for Definition of the Three-Dimensional Geodesic Structures in the Olinda＇s Historical Site

It is shown to be a relevant study involving terrestrial methods of measurement, such as： forward and backward intersections, geometric leveling, trigonometric leveling with short distance targeted and spatial positioning GNSS methods, for the definition of field reference points and field-object points located in rough terrain. The geodesic structures were implemented in the Historic Site of Olinda employing GNSS （global navigation satellite system） receivers, total stations and digital level. The historical site of Olinda was recorded by UNESCO as Historical and Cultural Heritage of Humanity. The study area is located in the center of the busiest site with a quite roughly relief. This area has been studied since 2007 involving Research of Scientific Initiation and Pos-Graduation Course. This paper aims to present the realized experiments for the implementation and definition of geodesic structures in environments with very rough relief, including large old houses and historic monuments.

改进萤火虫群算法协同差分隐私的干扰轨迹发布

针对历史轨迹加噪发布干扰轨迹时数据集的冗余问题和轨迹形状相似带来的隐私泄露风险,提出轨迹数据先约简后泛化再进行差分隐私加噪的基于改进萤火虫群优化求解的干扰轨迹发布保护机制(IGSO-SDTP)。首先,基于位置显著点约简历史轨迹数据集;其次,结合k⁃匿名和差分隐私对简化后的轨迹数据集分别进行泛化和加噪;最后,设计了兼顾距离误差和轨迹相似性的加权距离,并以加权距离为评价指标,基于改进萤火虫群优化(IGSO)算法求解加权距离小的干扰轨迹。在多个数据集上的实验结果表明,与RD(Differential privacy for Raw trajectory data)、SDTP(Trajectory Protection of Simplification and Differential privacy)、LIC(Linear Index Clustering algorithm)、DPKTS(Differential Privacy based on K-means Trajectory shape Similarity)相比,IGSO-SDTP方法得到的加权距离分别降低了21.94%、9.15%、14.25%、10.55%,说明所提方法发布的干扰轨迹可用性和稳定性更好。

高密度芯片激光钎焊温度场及应力场数值模拟研究

旨在探讨激光钎焊工艺参数对高密度芯片制造中凸点焊点质量的影响。通过有限元方法建立了三维瞬态热耦合数值模型,并利用高斯体热源模型和iSoldering软件模拟了SnAgCu钎料凸点激光钎焊的温度场和应力场,研究不同功率10 W、15 W、20 W和不同光斑半径0.09 mm、0.3 mm、0.5 mm下SnAgCu钎料钎焊焊点的变化规律。研究发现,激光功率和光斑半径是影响焊点质量的关键参数。在部分参数不变的情况下,随着激光功率的增大,钎料熔化更完全,润湿性更好,但也会产生更大的等效应力。增大光斑半径会导致焊点温度和等效应力降低。经过数值模拟和实际钎焊焊点的对比,结果表明:当激光功率为15 W、光斑半径为0.09 mm、焊接速度为0.1 mm/s时,SnAgCu凸点激光钎焊的焊点质量最佳,模拟凸点钎焊的焊点与实际钎焊结果吻合度达到85%,验证了模拟结果的准确性和可靠性。同时探讨了钎料与焊盘之间生成的金属间化合物厚度对焊点质量的影响,为提高焊点连接强度提供了理论依据。

基于励磁电流控制的DESG风电机组MPPT控制

根据风力发电系统的要求研究了两种基于励磁电流控制的电励磁双凸极风力发电机(DSEG)系统最大风能跟踪(MPPT)控制策略。与传统MPPT方法不同,在此提出方法是利用DSEG的励磁电流来控制电磁转矩,从而间接控制发电机转速,实现最大风能跟踪控制。搭建了低速直驱电励磁双凸极风力发电机系统的仿真模型,对系统的工作特性进行了仿真对比研究。并以一台10 kW,48/32极低速DSEG为例,对提出的最大风能跟踪控制策略进了实验研究,仿真和实验结果表明所提MPPT控制策略的可行性与有效性。

基于RD-YOLO的毫米波雷达和视觉融合显著性目标检测

为了解决单传感器在复杂环境下目标检测精度低问题,提出了一种基于RD-YOLO的毫米波雷达和视觉融合的显著性目标检测方法。首先设计了能够将毫米波雷达点云转换为图像的方法,使毫米波雷达和视觉数据在模型输入时实现特征融合;然后通过动态互补注意力机制,对两个图像分支生成特征设置空间和通道动态注意力权重;最后采用YOLOv8检测融合后特征,引入改进损失函数Focal Loss以解决样本不均衡问题。在数据集nuScenes上开展的相关实验表明,与YOLOv5、YOLOv7、YOLOv8、Faster R-CNN和FCOS相比,所提方法目标检测综合性能良好,均值平均精度比原始YOLOv8提升了9.19%。

A Precise Calibration Method on Phase Center of Uplink Antenna Array Considering Its Actual Pointing

With regard to the inferior techniques and low accuracy of phase center calibration of an antenna array, this paper proposes a new calibration method considering the actual antenna pointing by introducing a precise engineering surveying technique to measure the real state of antennas. First, an industrial photogrammetric system is utilized to obtain the coordinates of points on antenna panels in different postures, and the actual pointing of the mechanical axis is obtained via least-squares fitting. Then, based on this, the coordinates of antenna rotation center are obtained by seeking the intersection of mechanical axes via using the matrix method. Finally, the mechanical axis in arbitrary postures is estimated based on the inverse-angle weighting interpolation method, and the reliable phase center is obtained by moving a fixed length from the projective center along the mechanical axis. An uplink antenna array including three ? 3 m antennas is taken as experimental object, and all photogrammetric coordinate systems are unified by the engineering control network, with each antenna phase center precisely calibrated via the proposed method. The results of electrical signal synthesis indicate that this method can effectively overcome the influence of gravity deformation and mechanical installation error, and enhance the synthetic signal magnitude of the uplink antenna array.

A High Speed Detection Scheme for Point Targets in a Multitarget Environment

The purpose of this paper is to develop a high speed detection scheme for moving and / or stationary point targets in a multitarget environment as registered in an IR image sequence. An iterative approximate 3-D line searching algorithm based upon the geometric representation of lines (for non-maneuvering targets in space) in a 3-D space is derived. The convergency of the algorithm is proved. An analysis is performed of the theoretical detection performance of the algorithm. The statistical experiment results show high effectiveness and computational efficiency of the algorithm in the case of low SNR. The idea may be employed to satisfy the real-time processing requirement of an IR system.

Overview of 3D Scene Viewpoints evaluation method

The research on 3D scene viewpoints has been a frontier problem in computer graphics and virtual reality technology.In a pioneering study,it had been extensively used in virtual scene understanding,image-based modeling,and visualization computing.With the development of computer graphics and the human-computer interaction,the viewpoint evaluation becomes more significant for the comprehensive understanding of complex scenes.The high-quality viewpoints could navigate observers to the region of interest,help subjects to seek the hidden relations of hierarchical structure,and improve the efficiency of virtual exploration.These studies later contributed to research such as robot vision,dynamic scene planning,virtual driving and artificial intelligence navigation.The introduction of visual perception had The introduction of visual perception had contributed to the inspiration of viewpoints research,and the combination with machine learning made significant progress in the viewpoints selection.The viewpoints research also has been significant in the optimization of global lighting,visualization calculation,3D supervising rendering,and reconstruction of a virtual scene.Additionally,it has a huge potential in novel fields such as 3D model retrieval,virtual tactile analysis,human visual perception research,salient point calculation,ray tracing optimization,molecular visualization,and intelligent scene computing.