Technical Summaries of GEMS

GEMS is a solid modelling system running on CAS workstation or 32 bits microcomputer with graphics terminal.Complex solid obj ects are built from transformation and set operations upon box,cylinder,cone,sphere,torus,sweeping object and other primitives.CEMS has explicit reatures.e.g.hierarchical modular structure, interactive user interfaceintuitional input,screen menu driven by data table,defining and instancing object in network construction,storage bases on CSG(Constructive Solid Geometry)and BReps(Boundary Representations).regularized set operations,transformation pipeline consistent with PHIGS graphics standard,various transformations,cutting object with two sections in arbitrary angle,patrolling to view the inside of an object,mapping patterns onto surfaces of an object etc.,Not only can it be used for the fields of spatial planning,architectural plan,CAD/CAM for machining,structure analysis,but it is also fundamental for developing the practical system of simulation,computer vision,robotics and so on.     

Constructive texturing based on hypervolume modeling

The concept of solid texturing is extended in two directions: constructive modeling of space partitions for texturing and modeling of multidimensional textured objects called hypervolumes. A hypervolume is considered as a point set with attributes of both physical (density, temperature, etc.) and photometric (color, transparency, diffuse and specular reflections, etc.) nature. The point set geometry and attributes are modeled independently using real‐valued scalar functions of several variables. Each real‐valued function defining 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 approach provides a framework for modeling, texturing and visualization of 3D solids, time‐dependent and multidimensional objects in a completely uniform manner. We introduced a special modeling language and implemented software tools supporting the proposed approach. The concept of constructive hypervolume textures is independent of the geometry representation. We provide examples of textured Frep and BRep objects as illustrations. Copyright © 2002 John Wiley & Sons, Ltd.     

Adaptive space decomposition for fast visualization of soft objects

We present a fast visualization scheme of soft objects by introducing an efficient evaluation method for a field function. The evaluation of a field function includes distance computation between a point in space and the defining primitives of the soft object. If the unnecessary distance computations between a point in space and the components that do not influence the point can be avoided, the evaluation can be accelerated. For this purpose, we decompose the space into adaptive‐sized cells according to the bounding volume of the components and build a data structure called an interval tree through which the influencing components for a point are sought. The bounding volume of a component is generated by considering the radius of a component and k‐DOPs. The proposed scheme can be used in many applications for soft objects such as modeling and rendering, especially in the interactive modeling process. Copyright © 2003 John Wiley & Sons, Ltd.     

图像驱动的三维模型外观细节增强

随着计算机游戏与电影视觉特效的普及应用,仅通过纹理贴图已不能满足用户需求。然而,为三维模型制作视觉真实的表面外观,即在包含几何细节变化(如金属腐蚀、石料风化、木质裂纹等)同时辅之以与几何变化合理匹配的材质颜色却是一件困难且耗时的工作。文章提出了一种能够从单幅图像中提取物体的外观细节(材质与几何信息)并增强至三维模型表面的方法。该方法是一种新型的几何约束的非刚性2D-3D融合配准算法,可以通过将配准后的模型提供的几何信息作为先验知识实现更好的本征图像分解结果。利用图像中同步分解出的互相关的多尺度几何信息与材质纹理信息组成的非参数外观模型,文中提出了一种法向量约束的几何变形算法将外观纹理恢复到代理模型上。通过上述步骤,文章提出的方法能够帮助建模师制作具有多尺度外观细节的三维模型。     

基于图像表达复杂物体的方法研究

在虚拟现实应用中,传统的建模方法是用图形建模的方法对每一个物体进行建模。在场景中,往往有很多物体是非常复杂甚至难以建模的。为了使建模工作简化并同时保证逼真度,提出一种基于图像表达复杂物体的方法。可以对某个复杂物体拍摄或制作多张对应不同视点方向的图像,并且在程序中用图的数据结构管理。在漫游浏览时,再根据摄像机的当前位置确定显示对应视点方向的图像。这种方法既可保证场景的逼真度,同时又使场景得到简化,使系统的运行速度得到提高。     

Interactive clipping techniques for texture-based volume visualization and volume shading

We propose clipping methods that are capable of using complex geometries for volume clipping. The clipping tests exploit per-fragment operations on the graphics hardware to achieve high frame rates. In combination with texture-based volume rendering, these techniques enable the user to interactively select and explore regions of the data set. We present depth-based clipping techniques that analyze the depth structure of the boundary representation of the clip geometry to decide which parts of the volume have to be clipped. In another approach, a voxelized clip object is used to identify the clipped regions. Furthermore, the combination of volume clipping and volume shading is considered. An optical model is introduced to merge aspects of surface-based and volume-based illumination in order to achieve a consistent shading of the clipping surface. It is demonstrated how this model can be efficiently incorporated in the aforementioned clipping techniques.     

Data Management in Networks: Experimental Evaluation of a Provably Good Strategy

This paper deals with data management for parallel and distributed systems. We present the DIVA (Distributed Variables ) library that provides direct access to shared data objects from each node in a network. The current implementations are based on mesh-connected massively parallel computers. Our algorithms dynamically create and discard copies of the data objects in order to reduce the communication overhead. We use a non-standard approach based on a randomized but locality preserving embedding of ``access trees' into the network. The access tree strategy was previously analyzed only in a theoretical model. A competitive analysis proved that the strategy minimizes the network congestion up to small factors. In this paper the access tree strategy is evaluated experimentally. We test several variations of this strategy on three different applications of parallel computing, namely matrix multiplication, bitonic sorting, and Barnes—Hut N -body simulation. We compare the access tree strategy with a standard caching strategy using a fixed home for each data object. Our experiments show that the access tree strategy outperforms the fixed home strategy clearly as it avoids network congestion. Furthermore, we do comparisons with hand-optimized message passing strategies. In fact, we observe that the access tree strategy comes reasonably close to the performance of the hand-optimized message passing strategies while the fixed home strategy performs poorly. Received in final form October 8, 2001. Online publication March 25, 2002.     

GosiP: A GKS3D Shell for PHIGS

Gosip is an implementation of a GKS-3D level 2c interface to PHIGS. It allows GKS applications to run on PHIGS platforms, offering performance and portability across a wide range of high-performance 3D workstations. Compatibility of the standards is reviewed. A selection of design solutions is given for the problems of error processing, non-retained primitives and attribute management. The concepts of Workstation Display Session and atmbute state are introduced. Some comments are made on implementation dependencies, performance and portability.     

A Library for Developing PHIGS Programming Tools in a PEX Environment

The merger of three-dimensional graphics with the X Window System has recently been standardized by adapting PHIGS, the Programmer's Hierarchical Interactive Graphics System, to the X Window System with PEX, the PHIGS Extension to X. The standard programming library for PEX has been defined to be identical to PHIGS PLUS allowing PHIGS programs to port directly to the X environment. X uses a client server model to run applications as client processes which communicate with a server to perform graphical display and input. For improved performance, the PEX extension defines new server resources to reduce network traffic and to take advantage of graphics hardware existing on high-end servers. A side effect of this distributed model of computation is a distribution of PHIGS structures leading to a relaxation of the exclusive access which a PHIGS application usually maintains over its Central Structure Store. We exploit the distributed nature of a PEX/PHIGS client's Central Structure Store to provide access to it for other applications besides the originating PEX/PHIGS client. We refer to these other applications as tools since one of our primary goals is to create development tools for PHIGS programmers. Rather than concentrate on particular debugging tools, we focus upon easing the process of actually developing tools. Our goal is to supply a collection of routines which can be used by PHIGS programmers to create custom tools or other programs which require access to the graphics data of remote PHIGS processes. Our Tool Development Library provides the PHIGS programmer a small number of management routines which orchestrate the connection and mapping to the data of one or more remote PHIGS applications. Manipulation of remote PHIGS structures is accomplished just as easily as local operations and is performed using standard PHIGS calls. The remote application being accessed requires no changes to its source code. Obvious uses for the Tool Development Library are in the construction of PHIGS tools such as structure browsers, editors and debugging aids. Less obvious is the potential for developing collections of cooperating graphics applications which share graphics data.     

网络风险评估方法研究

为了进行网络风险评估,采用隐马尔可夫随机过程作为分析手段,以入侵检测系统的输出（报警事件）为处理对象,建立了描述主机系统受到攻击后状态转化的隐马尔可夫模型(HMM),给出了主机系统风险指数的计算方法,并经过简单叠加得到整个网络风险的定量评价。最后通过实验证实了所提出方法的有效性。     

Heterogeneous and Multifaceted Multimedia Objects in DOOR/MM: A Role-Based Approach with Views

Although the distributed multimedia information system is getting popular nowadays, existing database systems do not offer adequate support to structural nor behavioral extension of multimedia objects. Moreover, the multifaceted nature of multimedia data has seldom been investigated. Besides the flexibility for multimedia authoring tools, dynamic extension and multifacet modeling can in general ease the task on integrating the multimedia information of heterogeneous formats over a distributed network. This paper presents the support of dynamic extension and multifacet modeling of multimedia objects in a client-server, object-role database system called DOOR. The resultant system, with multimedia functionalities, is named as DOOR/MM (DOOR with multimedia extensions). First, the underlying data model for DOOR is summarized. We then present the extension of the data model, by means of meta-object protocol (MOP), to implement the metaclasses for multimedia objects. In DOOR, objects are structured as a tree of roles. Each role may carry different properties and interact with other roles cooperatively. An object may acquire or drop multiple roles during its lifetime. Structural and behavioral extensions of multimedia objects are achieved by dynamic role playing. Multifaceted interfaces of an multimedia object are modeled by means of views on roles. In particular, we discuss different ways of using views to model different abstraction levels of the heterogeneous multimedia resources. Throughout the paper, examples such as text, bitmap, MIDI, and 3D graphic objects are used to demonstrate the significance of our approach.     

A Processor for an Object-Oriented Rendering System

An object oriented approach to the real-time rendering of raster images is described. The architecture is based on a set of object processors arranged in a pipeline. These object processors scan convert the objects in the scene and interpolate depth and normal vectors across the objects. Hidden surface elimination is distributed along the pipeline. The structure of the object processors and of the algorithms employed are described in detail.
Computing Reviews Classification: C. 1.2, C.3, 1.3.1     

移动对象数据库模型、查询语言及实时交通流分析

提出一种移动对象数据库模型——Dynamic Transportation Network Based Moving Objects Database(简称DTNMOD),并给出了DTNMOD中基于移动对象时空轨迹的网络实时动态交通流分析方法.在DTNMOD中,交通网络被表示成动态的时空网络,可以描述交通状态、拓扑结构以及交通参数随时间的变化过程;网络受限的移动对象则用网络移动点表示.DTNMOD 模型包含了完整的数据类型和查询操作的定义,因此可以在任何可扩充数据库(如PostgreSQL 或SECONDO)中实现,从而得到完整的数据库模型和查询语言.为了对相关模型的性能进行比较与分析,基于PostgreSQL 实现了一个原型系统并进行了一系列的实验.实验结果表明,DTNMOD 提供了良好的区域查询及连接查询性能.     

Factoring a Homogeneous Transformation for a more Efficient Graphics Pipeline

We identify an intermediate coordinate system situated between world coordinates and display coordinates, which exhibits unique features for lighting calculations and for clipping in homogeneous coordinates. Our key contribution is an algorithm for extracting such a coordinate system from a homogeneous viewing transformation that relates WC to DC. The algorithm is based on factoring the transformation into a product of a Euclidean factor and a sparse (computationally cheap) but non-Euclidean factor.
A particularly strong application of the proposed technique is the graphical processing of curved surface primitives, such as what is needed in the PHIGS PLUS viewing pipeline. Furthermore, in PHIGS PLUS the graphical data is retained by the graphics system, therefore, it is possible to perform the factoring of the viewing transformation at creation time, and to take advantage of this factored form at traversal time.     

Invariant fitting of planar objects by primitives

The determination of invariant characteristics is an important problem in pattern recognition. Many invariants are known which have been obtained by the method of normalization. In this paper, we introduce a new approach of fitting planar objects by primitives using the method of normalization (e.g., fitting by lines, triangles, rectangles, circles, ellipses, super-quadrics, etc.). Objects and primitives are described by features, for example, by moments. The main advantage is that the normalization process provides us with a canonical frame of the object and the primitive. Therefore, the fit is invariant with respect to the transformation used. By this new method, an analytical fitting of non-analytical objects can be achieved, for example, fitting by polygons. Furthermore, the numerical effort can be reduced drastically by normalizing of the object and the primitive     

MOQ-QR:基于QR-树的连续K近邻查询算法研究*

综合分析了R-树和四叉树在处理移动对象的连续K近邻（简称CKNN）查询算法中的不足,提出了一种基于R树和四叉树索引结构,去解决移动对象连续K近邻查询算法。该算法通过对移动对象分配静态空间,并在研究区域内利用QR-树和hash表作为索引去存储移动对象以此计算查询点与移动对象之间的空间距离。实验证明,该算法与现有算法相比,不仅提高了数据的查询效率,而且降低了系统资源的消耗。