A Progressive Line Simplification Algorithm

An application of line simplification considering spatial knowledge is described.A method for identifying potential conflict regions,in order to avoid the self_intersection of generalized lines,is also discussed.Furthermore,a new progressive line simplification algorithm is presented.From the view point of spatial cognition,a spatial hierarchical structure is proposed,and its application to construction of spatial knowledge related to a line is explained.

AN APPLICATION OF TOPOLOGICAL ANALYSIS TO STUDYING THE THREE-DIMENSIONAL FLOW IN CASCADES;PART I—TOPOLOGICAL RULES FOR SKIN-FRICTION LINES AND SECTION STREAMLINES

Based on the working of Lighthill and Hunt et al., in the present paper the author has established the topological rules adapting to analysing the skin-friction lines and the section streamlines in cascades. These rules are (1) for a rotor cascade without shroud band, the total number of nodal points equals that the saddle points on the skin-friction line vector fields in eachpitch range; (2) for an annular or straight cascade with no-clearances at blade ends, the total number of saddle points is two more than that of nodal points on the skin-friction line fields in a pitch; (3) the total number of saddles in the secondary flow fields on cross-sections in cascade is one less than that of nodes; (4) in the section streamline vector fields on a meridian surface penetrating a flow passage, and on leading and trailing edge sections, the total number of nodes is equal to that of saddles; (5) on the streamline vector fields of a blade-to-blade surface, the total number of nodes is one less than that of saddles.

Three-dimensional Model Analysis of Electric Field Excited by Multi-circuit Intersecting Overhead Transmission Lines

This work is carried out to predict the special distribution of electric field induced by multi-circuit intersecting overhead high-voltage (HV) transmission lines (TLs) within a large range without any expensive and time-consuming computation. The two main parts of the presented methodology are 1) setting up a three-dimensional (3D) model to calculate the electric field based on combining ca- tenary equations with charge simulation method and 2) calculating the hybrid electric field excited by multi-circuit intersecting TLs using coordinate transformation and superposition technique. Examples of different TLs configurations, including a 220 kV single-circuit hori- zontally configured TLs, a 500 kV single-circuit triangularly configured TLs and a combination of the 220 kV TLs and the 550 kV TLs, are illustrated to verify the validity of this methodology. A more complicatal configurations, including a 500 kV double-circuit TLs and two 220 kV single-circuit horizontally configured TLs, are also calculated. Conclusions were drawn from the simulation: 1) The presented 3D model outperforms 2D models in describing the electric field distribution generated by practical HV TLs with sag and span. 2) Coordinate trans- formation and superposition technique considerably simplify the electric field computation for multi-circuit TLs configurations, which makes it possible to deal with complex engineering problems. 3) The electric field in the area covered by multiple intersecting overhead TLs is distorted and the hybrid electric field strength in some partial region increases so sharply that it might exceed the admissible value. 4) The configuration parameters of the TLs and the spatial configuration of multi-circuit TLs, for instance, the height of TLs, the length of span and the intersection angle of multiple circuits, influence the strength and the distribution of hybrid electric field. The influence regularities sum- marized in this paper can be referred by future TL designs to meet the electromagnetic environmental protection regulations.

The Spatial Characteristics of a Line and Their Application to Line Simplification

This paper discusses the spatial knowledge related to a line ,and the characteristic points of lines is detected.According to the requirements of line generalization,new algorithms for identifying characteristic line points are presented.These characteristic points are used to improve the algorithms of line generalization.An algorithm for identifying bends is shown.In this paper,improved algorithms based on those by Douglas_Peucker,Visvalingam and Whyatt are shown.In this test,the progressive process of line generalization is emphasized.

A fast and precise three-dimensional measurement system based on multiple parallel line lasers

This paper conducts a trade-off between efficiency and accuracy of three-dimensional(3 D)shape measurement based on the triangulation principle,and introduces a flying and precise 3 D shape measurement method based on multiple parallel line lasers.Firstly,we establish the measurement model of the multiple parallel line lasers system,and introduce the concept that multiple base planes can help to deduce the unified formula of the measurement system and are used in simplifying the process of the calibration.Then,the constraint of the line spatial frequency,which maximizes the measurement efficiency while ensuring accuracy,is determined according to the height distribution of the object.Secondly,the simulation analyzing the variation of the systemic resolution quantitatively under the circumstance of a set of specific parameters is performed,which provides a fundamental thesis for option of the four system parameters.Thirdly,for the application of the precision measurement in the industrial field,additional profiles are acquired to improve the lateral resolution by applying a motor to scan the 3 D surface.Finally,compared with the line laser,the experimental study shows that the present method of obtaining 41220 points per frame improves the measurement efficiency.Furthermore,the accuracy and the process of the calibration are advanced in comparison with the existing multiple-line laser and the structured light makes an accuracy better than 0.22 mm at a distance of 956.02 mm.

Development of an In-Situ Laser Machining System Using a Three-Dimensional Galvanometer Scanner

In this study, a three-dimensional (3D) in-situ laser machining system integrating laser measurement and machining was built using a 3D galvanometer scanner equipped with a side-axis industrial camera. A line structured light measurement model based on a galvanometer scanner was proposed to obtain the 3D information of the workpiece. A height calibration method was proposed to further ensure measurement accuracy, so as to achieve accurate laser focusing. In-situ machining software was developed to realize time-saving and labor-saving 3D laser processing. The feasibility and practicability of this in-situ laser machining system were verified using specific cases. In comparison with the conventional line structured light measurement method, the proposed methods do not require light plane calibration, and do not need additional motion axes for 3D reconstruction;thus they provide technical and cost advantages. The insitu laser machining system realizes a simple operation process by integrating measurement and machining,which greatly reduces labor and time costs.

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

城市实景模型结构化线面特征重构方法

为了改善城市实景模型边缘模糊,提出了一种曲率引导的结构化线面特征重构方法。根据曲率特征将网格分割为平面、可展凹、可展凸以及不可展曲面4类,在平面分割结果内提取平面,在可展凹和可展凸分割结果内提取直线,对过度弯曲的不可展区域进行保留,最终形成包含几何特征的复合网格模型。结果表明,结合曲率信息预先设置几何特征的潜在范围,使得结构化线面特征更可靠,同时保证城市实景中复杂的树结构不被错误地提取为平面。

一种基于地面激光雷达点云的建筑物外轮廓自动提取方法

本文针对基于地面点云数据的建筑物轮廓自动提取,设计了一种由粗到精的提取方法。首先,将点云降维,在图像中进行轮廓优化和粗提取;然后,将欧式距离聚类和全局最小二乘方法与RANSAC方法结合,对提取出的粗轮廓进行更精细地拟合,得到原始的线要素;最后,采用平面几何拓扑约束和经验模型的方法,对得到的线要素进行简化和连接,完成轮廓的提取。试验结果表明,本文方法能够有效提取出建筑物轮廓,与传统方法实测相比,轮廓顶点处的位置精度总体小于5 cm,能够满足大多数城市测量应用场景。

大地导电率在特高压线路工程中的应用

本文以某特高压线路工程为案例,通过对称四极电测深采集野外数据,内业采用了量板法、简化法、计算法、测算量板法进行大地导电率的解译,并对比解译成果。通过对比分析,建议采用量板法与简化法两种方法同时处理,并对比成果的有效性。在采用量板法时,建议使用一维瑞典电阻率反演软件获得地下电阻率和岩土厚度来代替人工对比标准电测深曲线,以降低人为误差,提高内业资料处理效率。

Evaluation of Two Momentum Control Variable Schemes and Their Impact on the Variational Assimilation of Radar Wind Data:Case Study of a Squall Line

Different choices of control variables in variational assimilation can bring about different influences on the analyzed atmospheric state. Based on the WRF model＇s three-dimensional variational assimilation system, this study compares the be- havior of two momentum control variable options-streamfunction velocity potential （ψ-χ） and horizontal wind components （U-V）-in radar wind data assimilation for a squall line case that occurred in Jiangsu Province on 24 August 2014. The wind increment from the single observation test shows that the ψ-χ control variable scheme produces negative increments in the neighborhood around the observation point because streamfunction and velocity potential preserve integrals of velocity. On the contrary, the U-V control variable scheme objectively reflects the information of the observation itself. Furthermore, radial velocity data from 17 Doppler radars in eastern China are assimilated. As compared to the impact of conventional observation, the assimilation of radar radial velocity based on the U-V control variable scheme significantly improves the mesoscale dynamic field in the initial condition. The enhanced low-level jet stream, water vapor convergence and low-level wind shear result in better squall line forecasting. However, the ψ-χ control variable scheme generates a discontinuous wind field and unrealistic convergence/divergence in the analyzed field, which lead to a degraded precipitation forecast.

Evaluation of earthquake impact on magnitude of the minimum principal stress along a shotcrete lined pressure tunnel in Nepal

In situ stress condition in rock mass is influenced by both tectonic activity and geological environment such as faulting and shearing in the rock mass.This influence is of significance in the Himalayan region,where the tectonic movement is active,resulting in periodic dynamic earthquakes.Each large-scale earthquake causes both accumulation and sudden release of strain energy,instigating changes in the in situ stress environment in the rock mass.This paper first highlights the importance of the magnitude of the minimum principal stress in the design of unlined or shotcrete lined pressure tunnel as water conveyance system used for hydropower schemes.Then we evaluated the influence of local shear faults on the magnitude of the minimum principal stress along the shotcrete lined high pressure tunnel of Upper Tamakoshi Hydroelectric Project(UTHP)in Nepal.A detailed assessment of the in situ stress state is carried out using both measured data and three-dimensional(3D)numerical analyses with FLAC3D.Finally,analysis is carried out on the possible changes in the magnitude of the minimum principal stress in the rock mass caused by seismic movement(dynamic loading).A permanent change in the stress state at and nearby the area of shear zones along the tunnel alignment is found to be an eminent process.

Scaling properties of phase-change line memory

Phase-change line memory cells with different line widths are fabricated using focused-ion-beam deposited C-Pt as a hard mask. The electrical performance of these memory devices was characterized. The current^oltage （I-V） and resistance-voltage （RV） characteristics demonstrate that the power consumption decreases with the width of the phase-change line. A three-dimensional simulation is carried out to further study the scaling properties of the phase- change line memory. The results show that the resistive amorphous （RESET） power consumption is proportional to the cross-sectional area of the phase-change line, but increases as the line length decreases.

顾及面积差的层内等效二段线替代法优化声速剖面

声速剖面是多波束测深系统中至关重要的参数,针对声速剖面简化层内精度不高的问题,本文提出一种顾及层间面积差的声速剖面自适应分层优化方法——层内等效二段线替代法。基于声速最大偏移量方法,构建了一种优化替代声速剖面的最优层内等效二段线计算模型,并利用实测多波束测深数据对该算法进行了验证。通过实例分析发现该方法在多处地形起伏较大的区域,还原效果更好,更有效地保留了声速剖面特征点。统计结果表明,该方法可将整体水深数据和层间水深数据的标准差百分比控制在1%以内,在声速剖面等效面积差较大的深度,其计算的水深值更加接近原始声速剖面的计算结果。该方法可对复杂多层海水声速进行精确简化,在起伏较大的特殊海底地形的高精度测量中具有重要工程应用价值。

Three-dimensional elasticity solution of simple-supported rectangular plate on point supports, line supports and elastic foundation

This paper studies the bending of simple-supported rectangular plate on point supports, line supports and elastic foundation. On the basis of three-dimensional elasticity theory, the exact expressions of the displacement functions, which satisfy the governing differential equations and the simply supported boundary conditions at four edges of the plate, are analytically derived. The reaction forces of the in- termediate supports are regarded as the unknown external forces acting on the lower surface of the plate. The unknown coefficients are then determined by the boundary conditions on the upper and lower surfaces of the plate. Comparing the numerical results obtained from the proposed method to those obtained from Kirchhoff plate theory, Mindlin plate theory and those obtained from the commer- cial finite element software ANSYS, the high accuracy of the present method has been demonstrated.

基于区域候选网络的矢量线要素自动化简方法

针对现有矢量线要素化简算法智能化程度不高的问题,本文提出了一种基于区域候选网络的矢量线要素自动化简方法。首先利用深度可分离卷积神经网络实现矢量线要素栅格化后的卷积特征提取;然后结合线要素的坐标信息改进区域候选网络中候选框的生成方式,以实现候选框与可能的弯曲组合的对应;最后在统一线要素弯曲特征图大小的基础上,根据候选框对应的卷积特征进行二分类判断,完成弯曲单元的自动识别,并通过删除弯曲单元实现线化简。本文在海岸线数据集上进行了模型的训练和测试,并通过不同栅格化参数、不同骨干网络、跨尺度化简,以及不同类型线要素化简等对比试验验证了模型的有效性。试验结果表明,本文方法能够自动学习已有线化简案例中的化简知识,并充分利用线要素的矢量特征及栅格特征,自动完成线要素弯曲特征的准确定位,最终实现可端到端训练的矢量线要素自动化简。

Surveys on line drawing simplification for Chinese cultural computing

In the recent decade,many approaches of rough line drawing simplification were proposed,but they are not well summarized yet,especially from the perspective of Chinese cultural computing.In this paper,a comprehensive review of existing line drawing simplification methods was presented,including their algorithms,advantages/disadvantages,inputs/outputs,datasets and source codes,etc.For raster line drawings,related simplification work was discussed according to four main categories:fitting-based methods,tracing-based methods,field-based methods,and learning-based methods.For vector line drawings,a deep investigation was introduced for two major steps of simplification:stroke grouping and stroke merging.Finally,conclusions were given,key challenges and future directions of line drawing simplification for Chinese traditional art were thoroughly discussed.

一种顾及空间关系约束的线化简算法

线要素化简在制图表达与综合领域一直是研究的热点和难点之一。然而,经典化简算法多针对单独线要素进行处理,缺乏对该线要素与周边线要素之间整体空间关系的考虑,并且,存在计算结果生硬(D-P算法)、局部极值点缺失,特别是在曲度较大之处出现相交异常(L-O算法)等问题。为此,本文提出一种顾及空间关系约束的线化简算法,建立线要素全局化简方法(LGSM)和矢量位移、面积位移等5类评价指标。采用等高线、河流和道路3类线要素实际数据进行了试验,充分检验了本文算法的优越性,其处理结果符合开方根模型规律,降低了曲线复杂度,在保证全局空间关系不变条件下,不仅更好地保持了曲线整体形状特征,而且光滑美观、精度高。

曲线弯曲深度层次结构的二叉树表达

地图综合要顾及目标的几何特征、语义特征和拓扑特征 ,其中地理意义是控制综合算子选择、参量调整的决定性因素。就线状要素而言 ,单从角度、距离、矢高等几何特征出发设计的曲线化简算法只能算作对曲线坐标串的几何压缩 ,不是真正意义上的地图综合。由于曲线的弯曲特征在表达线状地物地理特征上具有重要意义 ,对弯曲特征的识别、结构描述及操作分析成为目前线要素制图综合的研究热点。本文基于约束 Delaunay三角网模型提出一种方法描述曲线弯曲特征在深度上的层次结构 ,对曲线上的矢量点构建三角网 ,在三角网覆盖区域里 ,由外向内进行三角形的“剥皮”操作 ,根据“剥皮”行进过程中遇到的特征三角形构建二叉树 ,实现大弯曲套小弯曲层次结构的表达。该方法基于 Gestalt对称性、连续性原则 ,对二叉树结点进行考察 ,可提取认知意义上的真正弯曲。本文同时给出了弯曲特征二叉树在多边形 (闭合曲线 )

Li-Openshaw算法的改进与评价

Li-Openshaw算法是一种基于客观综合自然规律的自适应线状要素综合算法,使用该算法可得到较合理真实的综合结果。在分析Li-Openshaw算法特点的基础上,依据线化简的原则和目的,对算法进行改进:①首先提出利用点与直线的关系来识别弯曲以找出所有局部极大值点的方法以保持曲线整体形状;②SVO圆形与待综合曲线发生多次相交时按照线的顺序索引找到第一个近似交点,选取与曲线上圆心与交点的中点最接近的原始数据点作为综合后的选取点。在此基础上,给出化简时间、位移标准差和位置误差等评价指标,提出基于分形理论的曲线形状结构特征的评估方法等对两种算法进行比较与评估,实验结果证明,同原算法相比,改进的Li-Openshaw算法在线化简中更好地保持曲线的整体形状,具有较高的位置精度,提高化简效率。