Spherical harmonic transforms for discrete multiresolution applications

On the sphere, global Fourier transforms are non Abelian and usually called Spherical Harmonic Transforms (SHTs). Discrete SHTs are defined for various grids of data but most applications have requirements in terms of preferred grids and polar considerations. Chebychev quadrature has proven most appropriate in discrete analysis and synthesis to very high degrees and orders. Multiresolution analysis and synthesis that involve convolutions, dilations and decimations are efficiently carried out using SHTs. The high-resolution global datasets becoming available from satellite systems require very high degree and order SHTs for proper representation of the fields. The implied computational efforts in terms of efficiency and reliability are very challenging. The efforts made to compute SHTs and their inverses to degrees and orders 3600 and higher are discussed with special emphasis on numerical stability and information preservation. Parallel and grid computations are imperative for a number of geodetic, geophysical and related applications where near kilometre resolution is required. Parallel computations have been investigated and preliminary results confirm the expectations in terms of efficiency. Further work is continuing on optimizing the computations.     

3D数字颅骨生物特征的球面调和分析

三维物体的识别关键问题是找到能准确描述三维形状特征的描述子。利用球面调和级数的空间正交分解特性,计算三维颅骨的空间分解特征向量,继而构造三维特征描述子。提出了判断特征描述子形似性的准则,试验验证对于重建和扫描的3D颅骨进行了有效的识别。     

用于3D模型检索的扩展距离球面调和表达

使用光线投射方法对3D模型定义了一个对应的球函数--扩展距离球函数,然后引入了球面调和分析方法,构造了一种对于平移、缩放和旋转变换具有不变性的特征向量,并用于基于形状的3D模型检索中.与基于向径方法结合,提高了检索的效果,扩大了应用范围.     

基于球面调和函数的漫反射表面快速光照技术的研究

基于图像的光照是计算机图形学中一个新的研究领域。本文研究了一种基于球面调和函数理论的快速光照技术,此方法采用三阶球面调和函数近似估计理想漫反射物体表面的光亮度,以此实现物体表面光亮度的计算。实验结果表明,本算法能够实现真实感图像的实时绘制。     

基于能量控制的球面谐波函数光照演示方法

目前在光照模型中常用球面谐波函数(SH)来表示不同的光特性,该函数可通过控制它的基函数因子数量得到不同的光照效果,而传统的方法存在过程复杂、抗干扰能力差的缺点,为此研究并提出了基于能量控制光照模型中球面谐波函数因子的理论,新方法考虑到图像压缩对SH的因子带来噪音,提出对量化过程进行建模,分析施加的能量约束条件,求解出最恰当的因子数.实验结果表明新方法在光照模型中能有效地控制球面谐波函数因子,其对应的图像效果也较好.     

一种球形机器人运动轨迹规划与控制

阐述一种非完整欠驱动系统的控制设计和运动规划策略 ,研制出一种全新的全方位行走机器人 ,由于其具有特殊的灵活性 ,可应用于各种不同的场合 .     

一种球形滚动机器人的路径跟踪控制器设计

对一种球形滚动机器人的路径跟踪问题进行研究,设计一种基于自适应滑模控制策略的路径跟踪控制器。所设计的路径跟踪控制器采用鲁棒滑模自适应增益控制律,能够有效实现带有扰动和不确定性的实际球形滚动机器人的路径跟踪。推导球壳纯滚动和无自转非完整约束下球形滚动机器人的运动方程,并在此基础上设计自适应滑模路径跟踪控制器。对于给定的参考几何路径,所设计的路径跟踪控制器能够确保路径跟踪误差在有限时间内收敛至很小的零邻域内。基于Lyapunov稳定性理论证明了闭环控制系统的稳定性,数值仿真与样机实验结果进一步验证了所设计的路径跟踪控制器的有效性。     

Workspace Atlases for the Design of Spherical 3-DOF Serial Wrists

In this paper, the physical model of the solution space of spherical 3-DOF serial wrists is established. The reachable workspaces are classified. The dexterous workspaces for such wrists are investigated based on the rotatability conditions for the spherical 4-bar mechanism. Using the theory of conformal transformation, we obtain plane figures of the reachable and dexterous workspaces. The atlases of the workspaces in the physical model of the solution space are plotted. These results are useful not only for designer overall to understand the relationship between the workspaces and link lengths of spherical 3-DOF serial wrists, but also for the design of the wrists.     

三维球形传感器电场强度测量仪

本文介绍高压下工频电场强度测量仪。它是用一个三维的球形传感器采集高压下的模拟电场强度信号，通过光导纤维传送到低压接收机进行解调和自动测量的一种仪表。     

一种基于球面调和函数的柔性体建模方法实现

给出了球面调和函数表达柔性体模型的原理,重点探讨了一种新的基于球面调和函数多尺度性的虚拟柔性体建模方法的实现机理。实验结果表明,该方法可以实现柔性物体的精确建模和实时表达,适合应用于虚拟现实的柔性物体碰撞检测、虚拟手术等对场景实时性要求较高的领域。     

A harmonic potential field approach for joint planning and control of a rigid,separable nonholonomic,mobile robot

The main objective of this paper is to provide a tool for performing path planning at the servo-level of a mobile robot. The ability to perform, in a provably-correct manner, such a complex task at the servo-level can lead to a large increase in the speed of operation, low energy consumption and high quality of response. Planning has been traditionally limited to the high level controller of a robot. The guidance velocity signal from this stage is usually converted to a control signal using what is known as an electronic speed controller (ESC). This paper demonstrates the ability of the harmonic potential field (HPF) approach to generate a provably-correct, constrained, well-behaved trajectory and control signal for a rigid, nonholonomic robot in a stationary, cluttered environment. It is shown that the HPF-based, servo-level planner can address a large number of challenges facing planning in a realistic situation. The suggested approach migrates the rich and provably-correct properties of the solution trajectories from an HPF planner to those of the robot. This is achieved using a synchronizing control signal whose aim is to align the velocity of the robot in its local coordinates, with that of the gradient of the HPF. The link between the two is made possible by representing the robot using what the paper terms “separable form”. The context-sensitive and goal-oriented control signal used to steer the robot is demonstrated to be well-behaved and robust in the presence of actuator noise, saturation and uncertainty in the parameters. The approach is developed, proofs of correctness are provided and the capabilities of the scheme are demonstrated using simulation results.     

一种球形机器人的非线性滑模运动控制

基于非线性滑模控制方法,对一种欠驱动的球形机器人的运动控制问题进行了研究．球形机器人的输入由两个相互正交的力矩组成．在非完整约束的条件下,分别建立球形机器人的运动学和动力学模型,并通过输入变换将动力学模型变换为一个两输入的二阶系统．基于非线性滑模控制方法分别设计了横向姿态控制器和纵向速度控制器,可以保证被控的运动状态收敛到期望的邻域内．仿真和实验结果验证了所建立的动力学模型和控制方法的有效性．     

基于MATLAB的球谐函数M函数库

以MATLAB为设计语言,开发了系列用于原子轨道球谐函数Y_(1m)(θ,φ)如s、p、d、f原子轨道及sp~3和d~2sp~3杂化轨道角度函数可视化的精确、快速、简便的m函数库。根据球坐标的自变量定义域:φ∈[0,2π]、θ∈[0,π],设定离散的自变量值T,P,对球谐函数Y_(1m)(θ,φ)及杂化轨道角度函数的解析式进行计算机程序化,根据解析式计算对应的R值,然后由MATLAB矩阵变换命令[X,Y,Z]=sph2cart(T,P,R)和绘图命令mesh(X,Y,Z)实现球谐函数Y_(1m)(θ,φ)及杂化轨道角度函数的可视化。详细介绍了程序设计思路、编写方法,给出了球谐函数Y_(1m)(θ,φ)及杂化轨道角度函数的解析式数组算法表达式、m-file绘图程序和运行结果。     

变化光照目标图像合成的球调和方法

光照是真实感绘制技术中的一个关键因素。研究了朗伯反射的球调和表示，提出了一种基于球调和函数的任意光照目标图像生成方法。该方法在给定目标基图像及其对应光照属性的基础上，通过基图像数据矩阵的奇异值分解（SVD）分离场景环境光分量、反演计算场景反射率和表面法向量等。新光照条件下绘制图像时，采用四阶球调和函数拟合入射光和朗伯反射核计算直接光照；间接光照采用分离出的基图像环境光分量拟合。实验表明：该方法能够保证绘制精确度，适合复杂光照条件下的目标图像生成。     

一种球形移动机器人爬坡运动的自适应滑模控制

针对一种球形机器人爬坡运动的位置控制问题,提出了一种自适应滑模控制方法.基于对实际系统的合理简化,利用拉格朗日方法建立了球形机器人爬坡运动的动力学模型,并将动力学模型表示为状态空间形式.基于系统的状态空间模型,将整个系统划分为两个子系统,并分别定义各子系统的滑动面.将其中一个子系统的滑动面引入到另一个子系统的控制设计中,采用李亚普诺夫稳定性理论设计了滑模控制律,并通过自适应律在线调节其切换增益.从理论上分析了闭环控制系统的稳定性,并通过数值仿真和样机实验验证了所提控制方法的有效性.     

Lighting Estimation of a Convex Lambertian Object Using Redundant Spherical Harmonic Frames

An explicit lighting estimation from a single image of Lambertian objects is influenced by two factors: data incompletion and noise contamination. Measurement of lighting consistency purely using the orthogonal spherical harmonic basis cannot achieve an accurate estimation. We present a novel signal-processing framework to represent the lighting field. We construct a redundant spherical harmonic frame with geometric symmetry on the sphere S ². Spherical harmonic frames are defined over the generating rotation matrices about symmetry axes of finite symmetry subgroups of SO(3), and the generating functions are spherical harmonic basis functions. Compared with the orthogonal spherical harmonic basis, the redundant spherical harmonic frames not only describe the multidirectional lighting distribution intuitively, but also resist the noise theoretically. Subsequently, we analyze the relationship of the irradiance to the incoming radiance in terms of spherical harmonic frames, and reconstruct the lighting function filtered by the Lambertian BRDF (bidirectional reflectance distribution function). The experiments show that the frame coefficients of spherical harmonic frames can better characterize the complex lighting environments finely and robustly.     

球形移动机器人基于神经网络的反馈线性化运动控制研究与实验

实现了一种对球形移动机器人的滚动速度进行控制的方法.球形移动机器人的控制输入和状态输出间存在难以精确数学描述的非线性关系,本文采用径向基函数神经网络,以在线训练的方式建立了球形机器人输入与输出的非线性映射;然后采用反馈线性化方法,设计了球形机器人的速度控制器,该控制器由反馈线性化控制器和减小神经网络逼近误差的补偿控制器构成;给出了该控制器的实现步骤.多次实验结果表明,该方法可以实现球形移动机器人稳定的速度控制.     

球团矿强度微机测试系统

介绍微机、智能模块、PLC构成的控制系统在氧化球团强度测试机中的应用 ,阐述了控制系统的设计思想和工作原理 ,给出了具体的控制线路图 ,系统性能稳定可靠 ,测量精确快速 ,具有一定的推广价值。     

用球面向量法解机械手逆运动学问题

本文首先介绍球面向量理论。在以点O为原点的所有右手坐标系的集合与以O为中心的单位球面上的所有球面向量的集合之间存在一一对应的关系。从而坐标系的旋转变换等价于球面向量在单位球面上的运动。通过解球面向量三角形即可达到研究坐标系旋转变换的目的。球面向量法是与“旋转矩阵法”和“旋转向量法” (即,四元数法)完全不同的一种新方法,不仅可以用来建立机械手运动学方程,而且特别适用于解逆运动学问题。本文介绍了如何用球面向量法解机械手运动学问题,并给出了几种适于常见机械手的具体解法。     

Extracting a polyhedron from a single-view sketch: Topological construction of a wireframe sketch with minimal hidden elements

An essential prerequisite to construct a manifold trihedral polyhedron from a given natural (or partial-view) sketch is solution of the “wireframe sketch from a single natural sketch (WSS)” problem, which is the subject of this paper. Published solutions view WSS as an “image-processing”/“computer vision” problem where emphasis is placed on analyzing the given input (natural sketch) using various heuristics. This paper proposes a new WSS method based on robust tools from graph theory, solid modeling and Euclidean geometry. Focus is placed on producing a minimal wireframe sketch that corresponds to a topologically correct polyhedron.