A reversible watermarking scheme for two-dimensional CAD engineering graphics based on improved difference expansion

Difference expansion is widely used in reversible watermarking for raster images, but it cannot be applied to data with low correlation, due to its large distortion. In this paper, an improvement is made to difference expansion technology to make it suitable for two-dimensional (2D) computer-aided design (CAD) engineering graphics. Based on improved difference expansion (IDE), a reversible watermarking scheme for 2D CAD engineering graphics is proposed. First, all vertices of the 2D CAD engineering graphics are extracted, and then the relative coordinates of these vertices are calculated. Finally, the encrypted watermark is embedded into the scale factor of the relative coordinates by using IDE technology. Experimental results show that the proposed scheme has a large capacity, good imperceptibility, and is robust against operations such as transformation, rotation, and equal scaling.     

Object representation and recognition using mathematical morphology model

The integration of representation and recognition of rigid solid objects is becoming increasingly important in computer-aided design (CAD), computer-aided manufacturing (CAM), computer graphics, computer vision, and other fields that deal with spatial phenomena. The mathematical framework used for modeling solid objects is mathematical morphology, which is based on set-theoretic concept. The mathematical characteristics of these operators are investigated in order to achieve a formal theory. Using mathematical morphology as a tool, our theoretical research aims at studying the representation schemes for the dimension and tolerance of the geometric structure. Object features can be also extracted by using the mathematical morphology approach. Through a distance transformation, we can obtain the shape number, significant points database, and skeleton. We have also developed the object recognition, localization, and corner and circle detection algorithms.     

可视化供配电CAD系统的研究与开发

基于科学可视化、对象建模,面向对象的软件开发技术,在解决了图形系统快速开发的几个关键技术、对象关联实现方法及电网中电气元件潜在拓扑关系描述等问题的基础上,开发了功能较为完备的实用化供配电ＣＡＤ及管理系统软件。同时,通过开放数据库互联技术实现了图形系统、计算接口与数据库管理系统的集成,解决了系统动态扩充功能。此文对开发专业领域ＣＡＤ软件具有借鉴作用。     

基于三维实体模型的钢结构工业厂房CAD/CAM软件后处理系统

为提高钢结构工业厂房设计的准确性、精确度和工作效率,为某钢结构工业厂房CAD/CAM软件研制出基于三维实体模型的后处理系统.该系统基于面向对象的编程技术,抽象出描述实际结构零件几何信息、结构特征和设计条件的智能型实体对象.将对象以及对象之间的层次关系和逻辑关系存储在AutoCAD图形数据库中,形成三维实体模型,用于直观、准确和完整地表现具有复杂空间关系和细部构造的真实结构;实现数据库对象的建立、编辑、查询、显示和数据整理等操作.该系统结合具体结构形式的特点,实现用于施工图设计和深化设计的全部关键功能.     

协同图形编辑系统设计与实现

给出了基于图形对象的协同编辑系统的操作冲突／相容关系及其基于逻辑时间钟的检测方法和一致性保证算法。在此基础上，讨论了一个实时协同图形编辑系统的设计方面有关的关键技术。实验结果表明，该方法是可行和有效的。     

An Algorithm for Geometric Set Operations Using Cellular Subdivision Techniques

Geometric set operations play an integral role in systems for CAD/CAM, for robot planning, and for modeling objects such as underground formations from empirical data. Two major issues in the implementation of geometric set operations are efficiency in the search for geometric intersections and effectiveness in the treatment of singular intersection cases. This article presents an algorithm for geometric set operations on planar polyhedral nonmanifold objects that addresses both these issues. First, an efficient search for geometric intersections is obtained by localizing the search to small regions of object space through a cellular subdivision scheme using the polytree data structure. Second, an effective treatment of singular intersection cases is obtained by mapping each singular intersection occurring in a region into one of a small set of cases.     

Geometric assistance for visual reasoning and construction of solids with curved surfaces from 2D orthographic views

As the extensive use of solid models becomes widespread, it is important to have a mechanism by which existing engineering drawings can be converted into solid models. Therefore, a geometric assistance that can aid in visual reasoning and constructing of solid models is beneficial. In this paper, we present key operations for a system called the Assistant for Reasoning and Construction of Solids (ARCS), which provides this assistance given a set of two orthographic views. The geometric domain of ARCS encompasses curved solids with cylindrical and spherical surfaces, such as those found in typical mechanical parts. We have devised the Cylindrical and Spherical Warping operations to create cylindrical and spherical surfaces, which use interactive computer graphics that guide a human user to curved faces of a solid. These operations are then illustrated with examples using ARCS to create the solid models of typical mechanical parts from their orthographic projections.     

一种基于八叉树的三维实体内部可视化技术

鉴于传统的图形学-面图形学只能表达三维实体的表面的形状和属性，不能表达实体内部的属性，如纹理、密度场以及温度场等，因而在计算机图形学、CAD以及有限元分析等许多领域都需要一种新的可视化技术-三维实体的可视化技术，以表达实体内部的属性；三维实体的可视化技术是新兴的图形学-体图形学的一个重要组成部分，为了实现三维实体的可视化，针对CAD造型系统中的实际要求，根据体图形学的理论和八叉树的特点，提出了一种基于八叉树的实体内部可视化技术，该技术采用八叉树算法对边界数据结构表达的实体进行体元化。由于实体内部属性变化的不均匀，算法采用了不规则体元，以充分表达实体内部的细节，实际应用效果表明，该算法不但能充分表达实体内部属性，而且也具有一定的造型功能。     

XvgML语言的设计、优化及其与知识系统的集成

电气图是一种描述电气系统或装置的结构、原理、功能等的工程语言 ,在电气系统设计中具有十分重要的地位 .为此 ,给出了一种基于 XML(Extensible Markup L anguage)元语言实现的矢量电气图标记语言 Xvg ML(Ex-tensible Vector Graphics Markup L anguage) ,介绍了其设计、实现与优化过程 .Xvg ML 兼具表达几何特征和电气物理量 ,因而有效地克服了一些矢量图形语言对电气系统描述能力的不足 .Xvg ML 继承了 XML 的规范、简单、可扩展等特点 ,是一种对象化描述的信息语言 ,适合于与知识系统集成的应用 .Xvg ML 在基于 Web的智能设计系统、产品报价系统和异构系统数据交换等方面有着较好的应用前景     

Volume graphics

Volume graphics, which employs a volume buffer of voxels for 3D scene representation, is discussed. Volume graphics offers advantages over surface graphics: it is viewpoint independent, insensitive to scene and object complexity, and suitable for the representation of sampled and simulated data sets. Moreover, geometric objects can be mixed with these data sets. Volume graphics supports the visualization of internal structures and lends itself to the realization of block operations, constructive solid geometry modeling, irregular voxel sizes, and hierarchical representation. The problems associated with the volume buffer representation (such as discreteness, memory size, processing time, and loss of geometric representation) are discussed     

SVG应用中的图层处理算法

目前点阵图像依然是Web环境下表现图形的主要方式,由于其固有的弱点,难以满足实际应用需要.而少量的几种能够在Web环境下表现矢量图形的软件也存在着通用性差、可维护性差、开放性差等问题,不利于推广应用.基于SvG(scalable vector graphics)规范,构建具有多图层描述能力和开放式特征的矢量图形数据结构,设计并实现能够识别多层次结构的矢量图形变换算法,是解决Web环境下复杂图形处理任务的可行途径.利用G元素的可嵌套容器性质构建了支持多图层/图块的矢量图形数据结构;依托图形对象拾取与对象属性控制机制设计了图形对象的变换算法,据此通过脚本语言和DOM(document object model)编程实现了支持多图层结构的矢量图形表现与变换功能的方法.     

Constructive Hypervolume Modeling

This paper deals with modeling point sets with attributes. A point set in a geometric space of an arbitrary dimension is a geometric model of a real/abstract object or process under consideration. An attribute is a mathematical model of an object property of arbitrary nature (material, photometric, physical, statistical, etc.) defined at any point of the point set. We provide a brief survey of different modeling techniques related to point sets with attributes. It spans such different areas as solid modeling, heterogeneous objects modeling, scalar fields or “implicit surface” modeling and volume graphics. Then, on the basis of this survey we formulate requirements to a general model of hypervolumes (multidimensional point sets with multiple attributes). A general hypervolume model and its components such as objects, operations, and relations are introduced and discussed. A function representation (FRep) is used as the basic model for the point set geometry and attributes represented independently using real-valued scalar functions of several variables. Each function defining the geometry or an attribute is evaluated at the given point by a procedure traversing a constructive tree structure with primitives in the leaves and operations in the nodes of the tree. This reflects the constructive nature of the symmetric approach to modeling geometry and associated attributes in multidimensional space. To demonstrate a particular application of the proposed general model, we consider in detail the problem of texturing, introduce a model of constructive hypervolume texture, and then discuss its implementation, as well as the special modeling language we used for modeling hypervolume objects.     

A study on robot path planning from a solid model

CAD/CAM technologies have been developed and are beginning to penetrate rapidly into industries. At present, however, there are many problems that should be solved before CAD/CAM technologies can play their proper role in the total process. In an effort to improve CAD/CAM current circumstances, a trial CAE system which generates an operation path of a robot from a solid-model built-in CAD process, has been examined. In this system, solid models are built by performing set operations such as addition, subtraction, intersection between several primitives or solid models. Processing is made for a solid model represented by B-rep (boundary representation). To ease the processing, curved faces such as spherical, cylindrical, or conical surfaces, are approximated by several flat planes. As a first step, by assuming Gaussian spatial distribution for a painting gun, path planning of a painting robot for a convex solid body has been examined. A scanning plane is defined for each flat plane and a path of robot effector is generated on this plane.     

基于T-Spline的全自动几何拓扑修复方法

从高质量曲面网格生成的需求出发,提出了一种基于T-Spline的全自动几何拓扑修复方法.本文方法创新性主要可归纳为:1）对原有计算机辅助设计（Computer aided design,CAD）几何模型不进行任何修改保留其本真,自动识别CAD几何模型中常见不必要的几何特征,成功解决了CAD几何模型中存在的几何瑕疵,如短边、窄面、退化边、退化面、非连续光滑边界及尖锐特征等,利用新生成的"虚边"、"虚面"处理几何瑕疵,同时通过虚拓扑重构CAD几何模型的B-Rep;2）开发了一套CAD/CAE集成系统,统一了几何模型与计算分析模型,实现计算机辅助工程（Computer aided engineering,CAE）与CAD两者的无缝集成,所有拓扑修复操作及后续CAE分析计算均在同一环境下进行,避免了几何模型在CAE与CAD系统间进行转换时造成的数据丢失.该方法能够对复杂实体实现全自动几何拓扑修复及网格生成,实验表明,在保证不失真的前提下,修复后的几何模型能够生成质量良好的网格且能降低网格的生成规模,验证了本文方法的实用性和有效性,以满足工程实际分析的需要.     

基于图形对象的一致性维护问题的研究

针对实时协同图形编辑系统中一致性维护关键问题,提出了一种基于图形对象的并发控制算法。该算法扩展了面向文本编辑的分布式操作转换dOPT算法,满足图形对象属性级上数据一致性维护,同时通过预定义图形对象间的关联关系和位置属性约束规则,进行操作语义维护管理,使得实时协同图形编辑系统的一致性维护更为有效和完备。     

多版本技术中的对象标识及其压缩

协同编辑系统支持不同地域的协作者通过网络同时地编辑同一个文本或图形对象,其研究具有挑战性.介绍了协同图形编辑中的多版本技术,重点讨论了对象标识及其策略,给出所存在的问题.提出了一个全面的对象标识方案.该方案解决了以往方案不能处理具有依赖关系的操作和相同关系的操作的对象标识和系统维护问题.同时,随着编辑的进行和冲突的产生,对象标识会急剧膨胀,影响系统处理的效率,分析了对象标识压缩的规则,给出一个对象标识压缩方法,并对其有效性进行了分析.实例分析和实验结果表明,所提出的对象标识及其压缩方案提高了系统的效率.     

协同图形编辑系统中改进的多版本技术

基于版本复制的多版本技术采用全复制的系统结构实现协同图形编辑系统中冲突操作的意愿保证问题.每个版本存储了编辑过程中所有在此版本上执行过的操作,故存在同一操作被存储多次和操作存储量随编辑过程的继续出现大规模增加的情况.本文从冲突操作集合着手,提出了一种改进的多版本技术,通过理论证明和模拟实验结果表明这种改进的多版本技术能有效地克服以上问题.     

Program design of STL machine graphics realistic system

This topic is based on Auto CAD graphic input environment.It takes the STL format graphic files as the data exchange interface to do the research of STL interactive 3D realistic graphics displaying content.Through the analysis of the STL file format,in VC++6.0 programming environment,class if stream in the standard IO library was used for object class definition.And get line functions in the string class were called to read and bind STL file line by line.In data processing module,draw triangles in Open GL programming technology was applied to realize the visual display of the STL graphics,with the corresponding 3D entity data generated.Open GL graphics processing technologies were applied to display 3D graphics from STL files input or realistic program module,which contain the graphic transformation,light,materials,et al.Test reports were shared based on the test of the application system.Finally the program design of STL graphics realistic display system was completed based on research work,which has certain theoretical and practical significance in the aspect of engineering application.     

Graphic Objects: A Mathematical Abstract Model for Computer Graphics

This paper defines an abstract mathematical model for graphic systems which incorporates modelling operations. The model is based on the “graphic object” concept. A graphic object is an abstraction of a graphic entity. Graphic objects are a generalization of the Fiume graphic object concept, supporting modelling operations, which give the set of graphic objects an algebraic structure of vector space and booelan algebra. Fiume visualization formalism can be applied to graphic objects. Further, product operations of graphic objects are defined, which are a generalization of solid sweep operations. Graphic object products may be used to build common 2D and 3D objects such as triangles, squares, cubes, circles and spheres from lines and arcs.     

Editing 3D models on smart devices

This study proposes a 3D CAD system available on smart devices, which are now a part of everyday life and which are widely applied in various domains, such as education and robot industry. If an engineer has a new idea while traveling or on the move, or in the case of collaboration between more than two engineers, this 3D CAD system allows modeling to be performed in a rapid and simple manner on a smart device. This 3D CAD system uses the common multi-touch gestures associated with smart devices to keep the modeling operations simple and easy for users. However, it is difficult to input the precise geometric information to generate 3D CAD models by such gestures. It is also impractical to provide a full set of modeling operations on a smart device due to hardware limitations. For this reason, the system excludes several complicated modeling operations. This work provides a scheme to regenerate a parametric 3D model on a PC-based CAD system via a macro-parametrics approach by transferring the 3D model created on a smart device in an editable form to a PC-based CAD system. If fine editing is needed, the user can perform additional work on a PC after reconstruction. Through the developed system, it is possible to produce a 3D editable model swiftly and simply in the smart device environment, allowing for reduced design time while also facilitating collaboration. This paper discusses the first-ever system design of a 3D CAD system on a smart device, the selection of the modeling operations, the assignment of gestures to these operations, and use of operation modes. This is followed by an introduction of the implementation methods, and finally a demonstration of case studies using a prototype system with examples.