法向量约束下的蝶形细分曲面方法

文章提出一种以原网格的顶点的法向量为约束条件，通过对初始三角形控制网格迭代插值的非静态细分的几何造型方法。新方法的主要优点是插值点的计算是依据网格的局部几何特征而不是网格的入度。实例显示新的细分方法可以很好继承原始网格的形状特征。     

基于半边结构细分曲面的研究与实现

作为CAD和计算机辅助几何设计的重要技术之一,细分曲面为实体造型提供了新的离散造型方法.在阐述细分曲面主要思想基础上,采用Catmull-Clark四边形模式介绍细分曲面生成算法;并用半边结构表示和存储实体的面、边和点之间的拓扑关系.以Catmull-Clark模式为例基于半边数据结构演示细分曲面的生成.结果表明,细分曲面具有规则简单、易于实现、且在适当数据结构支持下仅需较少初始控制网格信息就可得到极限曲面的优点,因而细分曲面技术成为三维实体造型的一种有效途径.     

应用于ISAR大转角下的沿视线插值算法

极坐标格式算法(PFA)在逆合成孔径雷达(ISAR)成像算法中主要运用插值算法来解决目标散射点越距离徙动问题,其插值方法的选择决定了成像效率和运算速度。提出了一种沿雷达视线插值的方法,建立了ISAR大转角目标几何模型,对其进行理论推导得到方位向的精确插值形式,并对因非均匀采样造成的形变进行方位重采样。仿真实验表明,相较于传统插值算法,该算法有着运算速度更快、聚焦性更好的优点。     

自由曲线曲面造型理论发展综述

自由曲线曲面造型是研究在计算机中表达物体模型形状的技术。基于其理论的实用化系统在航空航天、汽车、造船、机械、建筑和电子等行业建模中得到了广泛的应用。自上世纪60年代Bezier曲线曲面面世至今,其领域发展了逼近、插值、空间分解、细分技术、多分辨率分析等理论及应用。文中论述了曲线曲面建模理论的产生、发展和应用过程,以及当前的研究状况和发展趋势。     

电信市场细分浅析

随着电信市场竞争的日趋激烈,市场细分工作已越来越受到企业的重视。本文首先简要介绍了市场细分的概念和目的,然后分析和探讨了针对电信行业应如何开展市场细分工作,最后总结了市场细分对电信市场营销的三点启示。     

LTE系统中基于改进样条插值的信道估计方法

上行控制信道(PUCCH)格式1/1a/1b在长期演进(LTE)系统中承载重要的控制信令,其信道估计对系统性能有着重要影响.普通循环前缀(CP)时,PUCCH格式1/1a/1b要利用时隙内3个连续排放的导频进行插值需要考虑二阶插值或者三次样条插值.为了使其在TD-LTE测试仪表系统中得到高效实现,分析了两种插值算法,并...     

四频激光陀螺脉冲细分技术

文章对传统的激光陀螺整脉冲计数方法的误差进行了分析,提出了一种能精确测量陀螺输出脉冲尾数的脉冲细分方法,并对该方法进行了误差分析.在此基础上,利用脉冲细分方法采集了某型四频激光陀螺的数据.理论分析和实验表明,脉冲细分方法的角分辨率优于0.1角秒.     

提升格式:多项式拟合的预测方法

本文研究提升格式中预测算子的设计问题,目前大多数预测算子,就其本质而言,属于插值预测的范畴,比数据的插值曲线更能代表数据包络线的低频成分,因此在某个局部,数据减去它的拟合预测值（而不是插值预测值）,更能体现提升格式的预测过程应该是局域高通滤波的设计原则,本文提供了四点二次,六点二次和六点三次多项式拟合的计算实例。     

空间细分插值的多色打印机分色算法

研究多色打印机的反向光谱特征化,提出了一种空间细分插值的分色算法,提高了打印机颜色转换模型的精度。该算法结合颜色分区理论和胞元划分的方法,首先搜索目标颜色所属胞元空间,然后利用光谱纽介堡方程对胞元进行空间细分插值,并将满足阈值要求的插值点的通道信号值作为最终输出值。检测颜色样本的实验数据表明算法的分色精度高,平均色差达到1.013NBS。新算法能够实现多色打印机从光谱数据到通道信号值的准确转换。     

聚束模式双基地SAR极坐标格式成像算法研究

 对于任意几何配置下的聚束模式双基地合成孔径雷达,本文在信号模型分析的基础上提出了一种可实现有效聚焦的极坐标格式成像算法.根据对聚束模式双基地SAR原始数据域空间频率采样特点的分析,算法在实现由极坐标到直角坐标的插值转换时,采用非线性插值采样方法,保持了PFA算法中将二维插值分解为两个一维插值的特点,因此计算流程、效率及性能和常规单基地聚束SAR的PFA成像算法相同.最后通过点目标仿真验证了算法的有效性.     

Geometric Correction for Uneven Quadric Projection Surfaces Using Recursive Subdivision of Bézier Patches

This paper presents a scheme for geometric correction of projected content for planar and quadratic projection surfaces. The scheme does not require the projection surface to be perfectly quadratic or planar and is therefore suitable for uneven low‐cost commercial and home projection surfaces. An approach based on the recursive subdivision of second‐order Bézier patches is proposed for the estimation of projection distortion owing to surface imperfections. Unlike existing schemes, the proposed scheme is completely automatic, requires no prior knowledge of the projection surface, and uses a single uncalibrated camera without requiring any physical markers on the projection surface. Furthermore, the scheme is scalable for geometric calibration of multiprojector setups. The efficacy of the proposed scheme is demonstrated using simulations and via practical experiments on various surfaces. A relative distortion error metric is also introduced that provides a quantitative measure of the suppression of geometric distortions, which occurs as the result of an imperfect projection surface.     

Improvement of Chang-Wu broadcasting cryptosystem using geometricproperties of lines

In 1991, Chang and Wu proposed a broadcasting cryptosystem using interpolating polynomials and geometric properties of circles. The Chang-Wu scheme can be further enforced by using a time-variant parameter and a one-way function to protect legal receivers' secrets from being disclosed. The authors present an improvement of the Chang-Wu scheme using geometric properties of lines. This improvement repairs the security flaws inherent in the original Chang-Wu scheme, while requiring fewer public parameters and less computing time     

基于椭圆曲线的限制代理签名方案

基于椭圆曲线提出了一个限制代谢签名者的代理签名次数和代理签名期限的代理签名方案。原始签名者在代理签名有效期内，能限制代理签名者的代理签名次数，当代理签名有效期过后，能收回代理签名权。该方案克服了通常的代理签名方案中一旦原始签名者将答名权委托给代理签名者，就无法控制代理签名者的代理签名次数，无法收回代理签名权的缺点，该方案是基于椭圆曲线，采用一次一密签名构造的，具有安全性高，速度快，密钥量小，便于实现等优点。     

实时地形渲染的细节增强算法研究

浏览多分辨率细节层次地形,当视点距离地面非常近,达到最高分辨率时,地形无法继续细化,影响浏览的连续性和视觉效果。针对这一问题,文中在应用Chunked LOD算法构建地形的基础上,以规则格网为处理单元,结合并改进了Kobbelt细分算法和分形技术,提出了实时细节增强的改进方案。该方案可以实时地添加富有真实感的高分辨率网格,避免了因过多细节增强引起的计算负荷。根据这一改进所做的实验结果表明,该方法在保持帧速连续的基础上,能实时有效地增加细节,满足逼真视效的需求。     

Plane curve matching under affine transformations

It is common to use an affine transformation to approximate the plane curve matching problem under a projective transformation. The plane curve itself can be used as an identity to solve the parameters of an affine transformation. The objective of the paper is to obtain a closed form solution to the transformation parameters using lower order derivatives of a plane curve. A unique solution to the parameters of an affine transformation with up to second order derivatives is presented using differential invariants as well as the available global information. In discrete space, derivatives are obtained by numerical means. Achieving accurate numerical derivatives is always a crucial application issue. Different differentiation filters were experimented with in calculating derivatives of discrete plane curves. The ICP (iterative closest point) method was employed to improve the results obtained by the proposed invariant scheme, which was believed to be an important step towards the practical use of differential invariant schemes.     

Derivation of an analytical expression for a physical process from an experimental curve with kinks

A technique for deriving an analytical expression describing an experimental curve with one or several kinks is proposed. Depending on the pattern of the partial processes involved in the resulting process, derivation is based on calculating either their sum or geometric mean. “Participation functions” of the processes, whose run is determined by the coordinate of the intersection point of the processes and the “accuracy parameter,” are introduced into these expressions in order to increase the approximation accuracy. The choice of these parameters provides a correspondence between the approximation accuracy and the accuracy of measuring the experimental curve. Application of this technique in analytical calculations consisting of a combination of several processes and in the derivation of an analytical expression for an experimental curve with kinks is demonstrated. The thus obtained approximating expression, characterized by clarity, a high approximation accuracy, and physical simplicity, may be used to calculate other characteristics of a semiconductor device.     

三维扫描系统细分驱动电路研究

以863课题“三维扫描仪”的高分辨率扫描为应用背景,提出了3种细分驱动电路系统方案：利用集成芯片UC3717AN的方案,利用IXMS150的方案以及利用分离电子元件组成的驱动电路方案.介绍了3种方案的实现方法并给出了电路图.试验证明这些方案能满足三维测量系统对扫描细分电路的要求.     

Optimization and FROC analysis of rule-based detection schemes using a multiobjective approach

Computerized detection schemes have the potential of increasing diagnostic accuracy in medical imaging by alerting radiologists to lesions that they initially overlooked. These schemes typically employ multiple parameters such as threshold values or filter weights to arrive at a detection decision. In order for the system to have high performance, the values of these parameters need to be set optimally. Conventional optimization techniques are designed to optimize a scalar objective function. The task of optimizing the performance of a computerized detection scheme, however, is clearly a multiobjective problem: we wish to simultaneously improve the sensitivity and false-positive rate of the system. In this work we investigate a multiobjective approach to optimizing computerized rule-based detection schemes. In a multiobjective optimization, multiple objectives are simultaneously optimized, with the objective now being a vector-valued function. The multiobjective optimization problem admits a set of solutions, known as the Pareto-optimal set, which are equivalent in the absence of any information regarding the preferences of the objectives. The performances of the Pareto-optimal solutions can be interpreted as operating points on an optimal free-response receiver operating characteristic (FROC) curve, greater than or equal to the points on any possible FROC curve for a given dataset and detection scheme. It is demonstrated that generating FROC curves in this manner eliminates several known problems with conventional FROC curve generation techniques for rule-based detection schemes. We employ the multiobjective approach to optimize a rule-based scheme for clustered microcalcification detection that has been developed in our laboratory.     

光电位移信号新型细分方法及系统设计

为提高光电轴角编码器的分辨力,提出一种新型莫尔条纹信号细分方法并建立基于FPGA的光电位移信号倍频系统.根据理想莫尔条纹光电信号的数学模型,利用多倍角正余弦信号的函数性质,将原始莫尔条纹信号推导为n倍频的高阶信号;由幅值细分理论,离线建立基于高阶正余弦信号的高分辨力幅值细分查找表;根据增量式、绝对式光电编码器的不同功能,分别阐述了应用该幅值细分查找表实现编码器高分辨力的倍频技术;同时又指出本文细分方法应用的约束条件.最后,以直径为40mm,分辨率为2500P/R的欧姆龙E6B2-CWZ6C增量式光电编码器为实验对象,在转速范围200~3000rpm的同步电机驱动下,编码器输出波形频率范围约为8.3kHz~125kHz,在基于频率为10kHz的模拟输入信号下,采用本文细分方案设置四倍频设计实验,该系统可以快速将频率增加到原来频率的4倍;同时,基于4倍频原理设计了128倍频实验,并进行实验验证,同样得到该系统可以快速增加到输入频率的128倍.该设计方法及系统与传统细分方法相比较,具有开发周期短、集成度高、模块化、速率快等特点.     

Landmark-based elastic registration using approximating thin-platesplines

We consider elastic image registration based on a set of corresponding anatomical point landmarks and approximating thin-plate splines. This approach is an extension of the original interpolating thin-plate spline approach and allows to take into account landmark localization errors. The extension is important for clinical applications since landmark extraction is always prone to error. Our approach is based on a minimizing functional and can cope with isotropic as well as anisotropic landmark errors. In particular, in the latter case it is possible to include different types of landmarks, e.g., unique point landmarks as well as arbitrary edge points. Also, the scheme is general with respect to the image dimension and the order of smoothness of the underlying functional. Optimal affine transformations as well as interpolating thin-plate splines are special cases of this scheme. To localize landmarks we use a semi-automatic approach which is based on three-dimensional (3-D) differential operators. Experimental results are presented for two-dimensional as well as 3-D tomographic images of the human brain.