Local Exact Particle Tracing on Unstructured Grids

For analyzing and interpreting results of flow simulations, particle tracing is a well established visualization method. In addition, it is a preliminary step for more advanced techniques such as line integral convolution. For interactive exploration of large data sets, a very efficient and reliable particle tracing method is needed. For wind channel experiments or flight simulations, large unstructured computational grids have become common practice. Traditional approachs, based on numerical integration methods of ordinary differential equations however fail to deliver sufficiently accurate path calculation at the speed required for interactive use. In this paper we extend the local exact approach of Nielson and Jung in such a way that it can be used for interactive particle tracing in large data sets of steady flow simulation experiments. This will be achieved by sophisticated preprocessing using additional memory. For further visual enhancement of the streamline we construct an implicitly defined smooth Bézier curve that is used for ray tracing. This allows us to visualize additional scalar values of the simulation as attributes to the trajectory and enables the display of high‐quality smooth curves without creating any visualization geometry and providing a good impression of the spatial situation at the same time. ACM CSS: I.3.3 Computer Graphics—Line and curve generation; I .3.7 Computer Graphics—Raytracing; G.1.2 Numerical Analysis—Spline and piecewise polynomial approximation     

The CORBA Activity Service Framework for supporting extended transactions

Although it has long been realized that ACID (atomicity, consistency, isolation, durability) transactions by themselves are not adequate for structuring long‐lived applications and much research work has been done on developing specific extended transaction models, no middleware support for building extended transactions is currently available and the situation remains that a programmer often has to develop application specific mechanisms. The CORBA Activity Service Framework described in this paper is a way out of this situation. The design of the service is based on the insight that the various extended transaction models can be supported by providing a general purpose event signalling mechanism that can be programmed to enable activities—application specific units of computations—to coordinate each other in a manner prescribed by the model under consideration. The different extended transaction models can be mapped onto specific implementations of this framework, permitting such transactions to span a network of systems connected indirectly by some distribution infrastructure. The framework described in this paper is an overview of the OMG's (Object Management Group) Additional Structuring Mechanisms for the OTS standard. Through a number of examples the paper shows that the framework has the flexibility to support a wide variety of extended transaction models. Although the framework is presented here in CORBA specific terms, the main ideas are sufficiently general, so that it should be possible to use them in conjunction with other middleware. Copyright © 2003 John Wiley & Sons, Ltd.     

Integration of CORBA and object relational databases

CORBA is widely accepted as the open international standard for modelling and building comprehensive distributed systems. In most cases, CORBA architects have adopted relational databases for storage of persistent data. Among the issues that usually face architecture designers considering how to combine CORBA and standard relational database standards are fault tolerance, performance, and the extensibility and scalability of the systems. The research team involved with this paper found that the ODMG object database concept is useful to solve the issues encountered when integrating CORBA and relational database standards. The reference architecture, which the team devises, integrates CORBA and relational databases without compromise on the necessary transactional properties. The CORBA standard object transaction service and concurrency control service are reused. The team also develop an object relational data modelling tool—Latte—that supports the overall design intention as well the development paradigms for the proposed architecture. The implementation of the system is useful to CORBA, ODMG, and relational database architects because it provides a unified modelling and programming paradigm capable of solving the problems of managing mission-critical distributed data. Thus, we present a case study of combining different international standards to build a comprehensive system.     

BRDF Measurement Modelling using Wavelets for Efficient Path Tracing

Physically based rendering needs numerical models from real measurements, or analytical models from material definitions, of the Bidirectional Reflectance Distribution Function (BRDF). However, measured BRDF data sets are too large and provide no functionalities to be practically used in Monte Carlo path tracing algorithms. In this paper, we present a wavelet‐based generic BRDF model suitable for both physical analysis and path tracing. The model is based on the separation of spectral and geometrical aspect of the BRDF and allows a compact and efficient representation of isotropic, anisotropic and/or spectral BRDFs. After a brief survey of BRDF and wavelet theory, we present our software architecture for generic wavelet transform and how to use it to model BRDFs. Then, modelling results are presented on real and virtual BRDF measurements. Finally, we show how to exploit the multiresolution property of the wavelet encoding to reduce the variance by importance sampling in a path tracing algorithm. ACM CSS: I.3.7 Computer Graphics—Three‐Dimensional Graphics and Realism     

基于CORBA/Web Service的PDM图档管理系统

从系统架构和功能需求分析入手,介绍了基于CORBA/Web Service技术开发的PDM图档管理系统,着重阐述了系统开发中的关键技术:IDL到WSDL的映射和CORBA对象的Web Service封装。针对CORBA现有IDL到WSDL映射规范中对复杂数据类型和接口继承的支持不够的情况下,提出了可以满足实际应用需求的映射规则,并实现了一个映射编译器——IDLW,从而实现了Internet范围内的图档数据访问和管理。     

CORBA request portable interceptors: analysis and applications

Interceptors are an emerging middleware technology enabling the addition of specific network‐oriented capabilities to distributed applications. By exploiting interceptors, developers can register code within interception points, extending the basic middleware mechanisms with specific functionality, e.g. authentication, flow control, caching, etc. Notably, these extensions can be achieved without modifying either the application or the middleware code. In this paper we report the results of our experiences with CORBA request portable interceptors. In particular, we point out (i) the basic mechanisms implementable by these interceptors, i.e. request redirection and piggybacking and (ii) we analyze their limitations. We then propose a proxy‐based technique to overcome the interceptors' limitations. Successively, we present a performance analysis carried out on three Java‐CORBA platforms currently implementing the portable interceptors specification. Finally, we conclude our work with a case study in which portable interceptors are used to implement the fault‐tolerant CORBA client invocation semantic without impacting on the client application code and on the CORBA ORB. We also release fragments of Java code for implementing the described techniques. Copyright © 2003 John Wiley & Sons, Ltd.     

Tracing Evolving Subspace Clusters in Temporal Climate Data

Analysis of temporal climate data is an active research area. Advanced data mining methods designed especially for these temporal data support the domain expert’s pursuit to understand phenomena as the climate change, which is crucial for a sustainable world. Important solutions for mining temporal data are cluster tracing approaches, which are used to mine temporal evolutions of clusters. Generally, clusters represent groups of objects with similar values. In a temporal context like tracing, similar values correspond to similar behavior in one snapshot in time. Each cluster can be interpreted as a behavior type and cluster tracing corresponds to tracking similar behaviors over time. Existing tracing approaches are for datasets satisfying two specific conditions: The clusters appear in all attributes, i.e., fullspace clusters, and the data objects have unique identifiers. These identifiers are used for tracking clusters by measuring the number of objects two clusters have in common, i.e. clusters are traced based on similar object sets. These conditions, however, are strict: First, in complex data, clusters are often hidden in individual subsets of the dimensions. Second, mapping clusters based on similar objects sets does not reflect the idea of tracing similar behavior types over time, because similar behavior can even be represented by clusters having no objects in common. A tracing method based on similar object values is needed. In this paper, we introduce a novel approach that traces subspace clusters based on object value similarity. Neither subspace tracing nor tracing by object value similarity has been done before.     

Robust Image Denoising Using a Virtual Flash Image for Monte Carlo Ray Tracing

We propose an efficient and robust image‐space denoising method for noisy images generated by Monte Carlo ray tracing methods. Our method is based on two new concepts: virtual flash images and homogeneous pixels. Inspired by recent developments in flash photography, virtual flash images emulate photographs taken with a flash, to capture various features of rendered images without taking additional samples. Using a virtual flash image as an edge‐stopping function, our method can preserve image features that were not captured well only by existing edge‐stopping functions such as normals and depth values. While denoising each pixel, we consider only homogeneous pixels—pixels that are statistically equivalent to each other. This makes it possible to define a stochastic error bound of our method, and this bound goes to zero as the number of ray samples goes to infinity, irrespective of denoising parameters. To highlight the benefits of our method, we apply our method to two Monte Carlo ray tracing methods, photon mapping and path tracing, with various input scenes. We demonstrate that using virtual flash images and homogeneous pixels with a standard denoising method outperforms state‐of‐the‐art image‐space denoising methods.     

基于CORBA的并行编程环境的设计与实现

作者设计并实现了一种基于CORBA模式的并行编程环境POVPE（并行面向对象可视编程环境）,它将传统的单机编程环境中的功能模块在分布式系统环境中进行了分布组织,并用CORBA完成分布模块的交互。文章介绍了该系统的功能描述和体系结构,着重阐述了瘦客户编程、实时远程编译、离线运行等关键技术,并从语言的角度给出了系统的实现方法。     

Parallel Multiple‐Bounce Irradiance Caching

Building designers rely on predictive rendering techniques to design naturally and artificially lit environments. However, despite decades of work on the correctness of global illumination rendering techniques, our ability to accurately predict light levels in buildings—and to do so in a short time frame as part of an iterative design process—remains limited. In this paper, we present a novel approach to parallelizing construction of an irradiance cache over multiple‐bounce paths. Relevant points for irradiance calculation based on one or multiple cameras are located by tracing rays through multiple‐bounce paths. Irradiance values are then saved to a cache in reverse bounce order so that the irradiance calculation at each bounce samples from previously calculated values. We show by comparison to high‐dynamic range photography of a moderately complex space that our method can predict luminance distribution as accurately as Radiance , the most widely validated tool used today for architectural predictive rendering of daylit spaces, and that it is faster by an order of magnitude.     

Using TRIO for designing a CORBA‐based application

We report on our experience in the Esprit OpenDREAMS project that targets the domain of Supervision and Control Systems (SCS). During this project we studied how a CORBA‐based application can be designed starting from a typical SCS requirement document by integrating a formal approach with some CORBA concepts. We present a case study that shows how an existing object‐oriented methodology based on the formal specification language TRIO can be tailored towards supporting CORBA‐based applications. The application taken into account is in the field of the Energy Management Systems, namely a diagnostic system for the steam condenser of a thermoelectric power plant. The paper describes how to obtain the architectural design of a CORBA‐based application starting from the formal specification of its requirements expressed in TRIO by means of a sequence of transformation steps. At the end of such sequence of steps a complete structure of the application classes, with their mutual relations and their IDL interfaces, is built. Finally, the paper discusses how TRIO can be used to validate the architectural choices made with respect to the application critical requirements. Copyright © 2000 John Wiley & Sons, Ltd.     

容错CORBA模型的研究与实现

容错CORBA是OMG组织为了适应分布式系统对容错性能的要求而对通用CORBA作的一个扩展，首先简要介绍了容错CORBA规范的一些基本概念以及相关研究，然后提出并实现了一个基于主动复制的容错CORBA模型，该模型利用全序服务实现了对象组成员处理请求的全序性，利用可靠服务保证了所有对象组的成员可以收到相同的请求报文，还在模型的调度机制上进行了研究并进行了系统的优化，实现了性能的提高．     

Integrate software agents and CORBA in computational grid

This paper presents an Agent-based Computational Grid (ACG), which applies the concept of CORBA and agent to computational grid. The ACG system is used to implement a uniform higher level management of the computing resources and services on the Grid, and provide users with a consistent and transparent interface for accessing such services. In ACG grid, grid services are implemented by CORBA or by grid agent. Grid agents and CORBA objects will interact with each other to achieve user's service request. Our solution is the creation of a bridge between the CORBA and grid agents. The solution provides with the opportunity of considering an agent as a CORBA service and accessing CORBA services even from a grid agent. Thus, in AGC grid, existing legacy systems can be easily exploited as grid services. In this paper, firstly, the features of ACG grid are described, and then the design and implementation are given. Finally, some conclusions are given.     

Extending Backward Polygon Beam Tracing to Glossy Scattering Surfaces

Backward polygon beam tracing methods, that is beam tracing from the light source (L), are well suited to gather path coherency from specular (S) scattering surfaces. These methods are useful for modelling and efficiently simulating caustics on diffuse (D) surfaces; an effect due to LS⁺D transport paths. This paper generalizes backward polygon beam tracing to include a glossy (G) scattering surface. To this end the details of a beam tracing lumped model and implementation of L(S | G)D transport paths are presented. Although we limit the discussion to short transport paths, we show that backward beam tracing is faster than photon mapping by an order of magnitude for rendering caustics from glossy and specular surfaces.     

CORBA技术的新发展

为了保持生命力,ＣＯＲＢＡ技术正在继续不断地发展,本文首先介绍ＣＯＲＢＡ的发展历程,在此基础上探讨了ＣＯＲＢＡ３．０的三个主要组成部分;ＣＯＲＢＡ服务,通过值传递对象和ＣＯＲＢＡ构件。随后简述了ＣＯＲＢＡ３．０的另外几个规范：嵌埋式ＣＯＲＢＡ,实时ＣＯＲＢＡ,Ｊａｖａ／ＩＤＬ映射,防火墙和ＤＣＥ／ＣＯＲＢＡ之间的协同工作。     

组件模型(CCM)的多视点分析

中间件与组件相结合正成为分布式系统开发的一个主要方向。CORBA是一个主流的中间件,最新的CORBA3.0规范增加CORBA组件模型(CCM),完成了CORBA向“组件化”转化的目标。文章分析了CCM产生的原因和背景,并运用IEEEStd1471多视点的分析方法,较全面的从各个视点剖析了CORBA组件模型,并给出了CCM的一个完整的多视点视图和基于CORBA组件的软件开发过程。最后指出了CCM需要进一步研究和完善的地方。     

利用CORBA和JDBC实现对各类关系数据库的访问

研究集成CORBA及关系数据库的三层式结构,并使用CORBA、Java及JDBC设计一个CORBA/RDBWrap-per,通过这个Wrapper,就可以很容易实现一个将CORBA与关系数据库集成起来的应用程序,而客户端通过支持Java的浏览器就可以访问关系数据库中的数据,进而达到分布式储存及计算的目的。     

Parallel Critical Path Tracing——A Fault Simulation Algorithm for Combinational Circuits

Critical path tracing,a fault simulation method for gate-level combinational circuits,is extended to the parallel critical path tracing for functional block-level combinational circuits.If the word length of the host computer is m,then the parallel critical path tracing will be approximately m times faster than the original one.     

Real-time CORBA

This paper presents a survey of results in developing Real-Time CORBA, a standard for real-time management of distributed objects. This paper includes background on two areas that have been combined to realize Real-Time CORBA: the CORBA standards that have been produced by the international Object Management Group; and techniques for distributed real-time computing that have been produced in the research community. The survey describes major RT CORBA research efforts, commercial development efforts, and standardization efforts by the Object Management Group.     

CORBA与DCOM桥接设计与实现

DCOM与CORBA是目前广泛使用的分布式技术,在开发大型的企业级分布式应用系统时,优先考虑使用的分布式技术就是DCOM或CORBA这两种中间件技术。有时一个系统需要同时使用DCOM与CORBA。由于这两者在具体的技术实现上有较大差别,使得它们在跨平台的互联时,不能直接实现DCOM与CORBA的互访。因此,如何实现系统中DCOM与CORBA直接通信成为一个关键问题。提出了一种实现DCOM和CORBA通信的桥接框架,是一种"动态桥",所需的桥接口可以随时添加到桥里,它解决了DCOM和CORBA之间不能通信的问题。