线框造型技术的再认识

本文讨论了利用三维线框作为骨架蒙上NURBS曲面后,产生与裁剪曲面和实体模型等价效果的产品建模技术。建立线框模型时采用离散的数据结构,各条边相互独立,便于设计修改。完成线框设计后,利用交互指点和自动搜索相结合的方法生成封闭的边环,然后蒙面。本法的优点是编程简便可靠,容易构造复杂度高的产品模型。     

由物体线框模型构建表面模型研究综述

三维重建过程中线框模型往往作为中间模型出现,由于线框模型的二义性以及过于简单的信息制约了它的应用,通常都要将其转换为表面模型或实体模型.该文主要围绕三维重建中线框模型的表面构建问题,分析其中所面临的难点.根据三维重建源对象的不同,对直接从线框模型提取特征构建表面模型、面向线框模型从单幅线图构建表面模型以及基于多面投影图构建表面模型三个方面,综述了当前对线框模型进行表面构建的方法.在此基础上指出研究中尚存在的问题并展望未来的发展趋势.     

基于直线检测的条码图像几何校正研究

CCD相机采集的图像会产生一定程度的几何变形,需要进行几何校正。常用的图像几何校正方法不适合条码图像的校正,因此,结合已有的边缘检测算法和直线提取算法,提出了基于直线检测的条码图像的几何校正算法。基于直线检测的条码图像校正方法是在已除去背景的图像中,寻找目标的条形码边缘对应的直线,以此确定其偏移角度,并进行扭转校正。实验结果表明,有偏转角度的条码图像运用了所提方法校正后,都得到了有效的几何校正。     

三维直线的表示及其约束

三维直线的表示是计算机图形学和计算机视觉中最基本的问题之一。在介绍了直线的表示原则以及分析了二维和三维直线的各种表示方法的基础上,选择并提出了适合三维重建的二维和三维直线表示方法：用法线式表示法表示二维直线;基于法线式表示法用垂直相交两平面表示法表示三维直线。提出了二维和三维直线的坐标概念,给出了正轴测投影和透视投影下三维直线之间的一些基本约束关系及其证明。     

双斜角度测量的计算公式

图纸上与基本投影面不平行的直线(可以为杆件、孔的轴线等的几何抽象)以及与基本投影面不垂直的平面,需用两个角度来限制其方向,故这些直线或平面称之为双斜直线或双斜平面。在实际测量中,由于图纸给定条件不同或基准面的变动,有时不能直接利用图上所标注的角度,而须进行角度换算。为使计算过程简便,本文推导出一套公式以供查用。一、双斜直线角度计算公式 (一)双斜直线方向双斜直线论其方向,仅有图1所示的直线AB、     

用R目镜测量圆锥螺纹中径

前言圆锥螺纹外径、内径、中径等几何参数均定义在给定基准面上；推度和基准距定义均与光滑圆锥相同；圆锥螺纹中径是一圆锥面，螺距是相邻两牙全尖牙顶间的距离，参见图1所示。本文只叙述牙形角平分线与螺纹轴线相垂直的圆锥外螺纹中径的测量，其它种类螺纹测量方法类同，仅仅是得出的中径计算公式不同而已。图1中，t：螺纹螺距；2吵：螺纹圆锥角8a／2：螺纹牙形半角。图1中，圆O的直径d0＝t’／2cos（a／2），d0即为最佳直径，与常说的最佳针径相对应。圆O与螺纹两牙例相切，M点为其切点，根据图示各几何参数之间的关系，易推知：△AMB…     

三维体素拼合及其在制图中的应用

本文介绍了一个小型三维造型系统，着重叙述了作者独立完成的物体拼合以及显示输出子模块中的三维线框模型输出，同时介绍了该软件在制图课教学中的应用。     

基于几何法立体图像校正的研究

立体视觉图像校正是加速立体匹配简单而常用的技术之一。采用几何法对使用棱镜的单镜头立体视觉系统图像进行校正,根据成像原理,从图像平面像素点反推到三维实体点的分析运算,利用成像光线几何关系求解虚拟相机外部参数,实现极线的校正,避免了复杂相机标定过程。同时,该算法可以从双棱镜应用推广到多面棱镜的单棱镜立体视觉系统图像校正。实验结果表明,基于几何法对使用棱镜的单镜头立体视觉系统图像校正是有效的。     

经纬仪几何关系的校正

1　前言经纬仪是一种测定目标的水平角和竖直角的大地测量仪器 ,不管是什么精度等级 ,不管是什么结构形式的经纬仪都有几条基本轴线 ,如竖轴、横轴、长水准器轴、望远镜视准轴等。轴线之间必须互相垂直或互相平行 ,这种轴线之间的关系在测量上就是仪器的几何关系。一台经纬仪如果几何关系校正不好 ,即使仪器很精密 ,也是测不出好结果的。特别是修理后或使用前一定要对几何关系进行校正 ,以保证经纬仪的准确可靠。下面就对各轴线的校正分述如下 :图 1　VV :仪器竖轴 ,HH :仪器横轴 ,CC :望远镜视准轴 ;LL :照准部长水准器轴2　照准部长水…     

基于贴近度的机械设备技术状态综合评估方法

讨论了模糊逻辑方法应用于技术状态综合评估的问题，提出了基于贴近度概念的技术状态综合评估方法；介绍了专家系统开发时，基准状态集的建立、基准状态中特征参数的选择、特征参数归一化处理模型等关键技术；讨论了专家系统的运行方式和知识库扩充的基本步骤。     

Estimation of Parameters of Universal Distribution of Moments of Failure of Products

A method is proposed for estimating the parameters of a mixture of exponential and Weibull distributions for which the accuracy of preliminary estimates obtained by graphical analysis is refined in accordance with the criterion of maximum likelihood. The efficiency of the proposed method is supported by the results of statistical modeling.     

Assessment of intakes of mixtures of radionuclides

Australia has several uranium mines and a large number of mineral sand mines, with associated processing facilities. Exposures resulting from these mining and processing operations usually involve intakes of mixtures of radionuclides. This work describes the development of a suite of first order, linear compartment models, based on the ICRP Publication 66 respiratory tract model, and an analytical solution to the decay equations, for assessing the consequences of such intakes. The computer programs based on these models directly compute excretion, organ retention and organ and whole-body doses for intakes of either single radionuclides or any mixture of radionuclides belonging to the same radioactive decay chain. The intake can be via inhalation, ingestion or injection, and can be acute, chronic or of limited duration. The starting concentration and degree of secular (dis)equilibrium can be specified for each radionuclide. No assumptions need to be made about the relative magnitudes of the radioactive half-lives of the different nuclides.     

Analysis of the rate of propagation of the wave of change of boiling modes

An approximate analytical expression is derived for the velocity of the front of the wave of change of boiling modes on a rod and on a plate. The impact of the Thomson effect and of the heater orientation in the gravity field is included. Adequate agreement is demonstrated between the derived relations and experimental data.     

Evaluation of optical properties of highly scattering media by moments of distributions of times of flight of photons

A novel method for the determination of the optical properties of tissue from time-domain measurements is presented. The data analysis is based on the evaluation of the first moment and the second centralized moment, i.e., the mean time of flight and the variance of the measured distribution of times of flight (DTOF) of photons injected by short (picosecond) laser pulses. Analytical expressions are derived for calculation of absorption and of reduced scattering coefficients from these moments by application of diffusion theory for infinite and semi-infinite homogeneous media. The proposed method was tested on experimental data obtained with phantoms, and results for absorption and reduced scattering coefficients obtained by the proposed method are compared with those obtained by fitting of the same data with analytical solutions of the diffusion equation. Furthermore, the accuracy of the moment analysis was investigated for a range of integration limits of the DTOF. The moment analysis may serve as a comparatively fast method for evaluating optical properties with sufficient accuracy and can be used, e.g., for on-line monitoring of optical properties of biological tissue.     

Analysis of anisotropy of properties on the basis of studies of texture of coarse-grained ingots of thermoelectric materials

An analysis of anisotropy of the properties of a Bi₂Se_0.3Te_2.7 solid solution was carried out using construction of demonstrative surfaces for thermoelectric effectiveness and thermal expansion coefficients. It is shown that the texture is an important factor forming anisotropy of properties and technological fitness of ingots for manufacturing modules. Anisotropy of properties based on the studies of the ingot textures obtained using the float-zone method and Bridgman method (growing thermoelectric plates in a flat cavity) was studied.     

Numerical study of methods of linearization of the output characteristics of radio-frequency sensors of the level of dielectric media

Different constructions of the sensing elements of radio-frequency level sensors based on sections of long lines are numerically investigated by means of the Matlab program for the purpose of minimizing the measurement error caused by the nonlinearity of the output characteristic. It is shown that the nonlinearity is lowest for U-shaped designs. The nonlinearity factor KN may be regulated by varying the capacitance of a correcting capacitor connected to the input of the sensing element and (or) the length of one of the sections of the long line. In selecting an optimal capacitance of the correcting capacitor KN ≤ 0.15% for control media with dielectric permittivity in the range 2.2–30.     

Possibilities of Decreasing the Errors of Determination of the Height of the Pole of a Sessile Drop of Melt

We analyze the possibilities of decreasing the errors of measuring the height of the pole of a sessile drop of melt above its equator by determining the position of the equator according to the midpoints of vertical chords of the image of the drop. The optimal distance between these chords and the edge of the image of the drop is chosen within 10–20% of the radius of the equator. The proposed method guarantees the same level of errors of evaluation of the height of the pole and the radius of the equator, which enables one to substantially increase the accuracy of evaluation of the capillary constant and the surface energy of the melt according to the geometric parameters of the sessile drop.     

Estimation of potentialities of methods of summation of direct measurement errors

Conventional methods for summation of direct measurement errors are considered. Conditions under which these methods provide consistent results are stated. It is proposed to utilize for characteristic of the total error, its interval estimator or the half-sum of the value obtained by adding up its arithmetic and geometric random errors.Translated from Izmeritel'naya Tekhnika, No. 4, pp. 10–12, April, 1995.