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Item Extending Graphics Hardware For Occlusion Queries In OpenGL(The Eurographics Association, 1998) Bartz, Dirk; Meißner, Michael; Hüttner, Tobias; S. N. SpencerFor interactive rendering of large polygonal objects, fast visibility queries are necessary to quickly decide whether polygonal objects are visible and need to be rendered. None of the numerous published algorithms provide visibility performance for interactive rendering of large models. In this paper, we propose an OpenGL extension for fast occlusion queries. Added after the depth test stage of the OpenGL rendering pipeline. our algorithm provides fast queries to establish the occlusion of polygonal objects. Furthermore, hardware aspects of this proposal are discussed and possible implementations on two different graphics architectures are presented.Item Tutorial 9 - Visibility(Eurographics Association, 1999) Chrysanthou, Yiorgos L.; Cohen-Or, Daniel; Fibich, Gadi; Halperin, Dan; Zadicario, Eyal; Lev-Yehudi, Shuly; Bartz, Dirk; Meißner, Michael; Hüttner, Tobias; Hüttner, Tobias; Bittner, Jiri; Havran, Vlastimil; Slavik, Pavel; Klosowski, James T.; Silva, Claudio T.The focus of this tutorial is a study of the techniques for solving visibility problems in virtual walkthroughs. The term walkthrough is referring not only to models of architectural models but rather to any large complex model, where the focus is on viewing and rendering the model. The tutorial touches on several applications such as fast visible surface determination, selection of relevant model sections to be transmitted on a client-server system, as well as improving image quality by shading algorithms.Item Advanced Algorithms in Medical Computer Graphics(The Eurographics Association, 2008) Klein, Jan; Bartz, Dirk; Friman, Ola; Hadwiger, Markus; Preim, Bernhard; Ritter, Felix; Vilanova, Anna; Zachmann, Gabriel; Theoharis Theoharis and Philip DutreAdvanced algorithms and efficient visualization techniques are of major importance in intra-operative imaging and image-guided surgery. The surgical environment is characterized by a high information flow and fast decisions, requiring efficient and intuitive presentation of complex medical data and precision in the visualization results. Regions or organs that are classified as risk structures are in this context of particular interest. This paper summarizes advanced algorithms for medical visualization with special focus on risk structures such as tumors, vascular systems and white matter fiber tracts. Algorithms and techniques employed in intra-operative situations or virtual and mixed reality simulations are discussed. Finally, the prototyping and software development process of medical visualization algorithms is addressed.Item Rendering and Visualization in Affordable Parallel Environments(Eurographics Association, 1998) Bartz, Dirk; Silva, Claudio; Schneider, Bengt-OlafThe scope of this full-day tutorial is the use of low and medium-cost parallel environments (less than US $ 60K) for high-speed rendering and visualization. In particular, our focus is on the parallel graphics programming of multi-processor PCs or workstations, and networks of both. The current technology push in the consumer market for graphics hardware, small multiprocessor machines, and fast networks is bound to make all of these components less expensive. In this tutorial, attendees will learn how to leverage these advances in consumer hardware to achieve faster rendering by using parallel rendering algorithms, and off-the-shelf software systems. This course will briefly touch the necessary tools to make basic use of this technology: parallel programming paradigms (shared memory, message passing) and parallel rendering algorithms (including image-, object-, and time- space parallelism). Advantages and issues of the different methods will be discussed on several examples of polygonal graphics and volume rendering.Item Tutorial 6 - Rendering and Visualization in Parallel Environments(Eurographics Association, 1999) Bartz, Dirk; Schneider, Bengt-Olaf; Silva, ClaudioThe continuing commoditization of the computer market has precipitated a qualitative change. Increasingly powerful processors, large memories, big harddisk, high-speed networks, and fast 3D rendering hardware are now affordable without a large capital outlay. A new class of computers, dubbed Personal Workstations, has joined the traditional technical workstation as a platform for 3D modeling and rendering. In this tutorial, attendees will learn how to understand and leverage both technical and personal workstations as components of parallel rendering systems. The goal of the tutorial is twofold: Attendees will thoroughly understand the important characteristics workstations architectures. We will present an overview of different workstation architectures, with special emphasis on current technical and personal workstations, addressing both single-processors as well as SMP architectures. We will also introduce important methods of programming in parallel environment with special attention how such techniques apply to developing parallel renderers. Attendees will learn about different approaches to implement parallel renderers. The tutorial will cover parallel polygon rendering and parallel volume rendering. We will explain the underlying concepts of workload characterization, workload partitioning, and static, dynamic, and adaptive load balancing. We will then apply these concepts to characterize various parallelization strategies reported in the literature for polygon and volume rendering. We abstract from the actual implementation of these strategies and instead focus on a comparison of their benefits and drawbacks. Case studies will provide additional material to explain the use of these techniques. The tutorial will be structured into two main sections: We will first discuss the fundamentals of parallel programming and parallel machine architectures. Topics include message passing vs. shared memory, thread programming, a review of different SMP architectures, clustering techniques, PC architectures for personal workstations, and graphics hardware architectures. The second section builds on this foundation to describe key concepts and particular algorithms for parallel polygon rendering and parallel volume rendering.Item Illustrative Hybrid Visualization and Exploration of Anatomical and Functional Brain Data(The Eurographics Association and Blackwell Publishing Ltd., 2008) Jainek, Werner M.; Born, Silvia; Bartz, Dirk; Straßer, Wolfgang; Fischer, Jan; A. Vilanova, A. Telea, G. Scheuermann, and T. MoellerCommon practice in brain research and brain surgery involves the multi-modal acquisition of brain anatomy and brain activation data. These highly complex three-dimensional data have to be displayed simultaneously in order to convey spatial relationships. Unique challenges in information and interaction design have to be solved in order to keep the visualization sufficiently complete and uncluttered at the same time. The visualization method presented in this paper addresses these issues by using a hybrid combination of polygonal rendering of brain structures and direct volume rendering of activation data. Advanced rendering techniques including illustrative display styles and ambient occlusion calculations enhance the clarity of the visual output. The presented rendering pipeline produces real-time frame rates and offers a high degree of configurability. Newly designed interaction and measurement tools are provided, which enable the user to explore the data at large, but also to inspect specific features closely. We demonstrate the system in the context of a cognitive neurosciences dataset. An initial informal evaluation shows that our visualization method is deemed useful for clinical research.Item Occlusion-Driven Scene Sorting for Efficient Culling(The Eurographics Association and Blackwell Publishing Ltd, 2006) Staneker, Dirk; Bartz, Dirk; Wolfgang, StrasserImage space occlusion culling is a powerful approach to reduce the rendering load of large polygonal models. However, occlusion culling is not for free; it trades overhead costs with the rendering costs of the possibly occluded geometry. Meanwhile, occlusion queries based on image space occlusion culling are supported on modern graphics hardware. However, a significant consumption of fillrate bandwidth and latency costs are associated with these queries.In this paper, we propose new techniques to reduce redundant occlusion queries. Our approach uses several "Occupancy Maps" to organize scene traversal. The respective information is accumulated efficiently by hardware-supported asynchronous occlusion queries. To avoid redundant requests, we arrange these multiple occlusion queries according to the information of the Occupancy Maps. Our presented technique is conservative and benefits from a partial depth order of the geometry.Item Rendering and Visualization in Parallel Environments(Eurographics Association, 2001) Bartz, Dirk; Silva, ClaudioThe continuing commoditization of the computer market has precipitated a qualitative change. Increasingly powerful processors, large memories, big harddisk, high-speed networks, and fast 3D rendering hardware are now affordable without a large capital outlay. Clusters of workstations and SMP-servers are utilizing these technologies to drive interactive applications like large graphical display walls (i.e., Powerwall or CAVE systems). In this tutorial, attendees will learn how to understand and leverage (technical and personal) workstation- and serverbased systems as components for parallel rendering. The goal of the tutorial is twofold: Attendees will thoroughly understand the important characteristics workstations architectures. We will present an overview of different workstation (Intel-based and others) and server architectures (including graphics hardware), addressing both single-processors as well as SMP architectures. We will also introduce important methods of programming in parallel environment with special attention how such techniques apply to developing cluster-based parallel renderers. Attendees will learn about different approaches to implement parallel renderers. The tutorial will cover parallel polygon and volume rendering. We will explain the underlying concepts of workload characterization, workload partitioning, and static, dynamic, and adaptive load balancing. We will then apply these concepts to characterize various parallelization strategies reported in the literature for polygon and volume rendering. We abstract from the actual implementation of these strategies and instead focus on a comparison of their benefits and drawbacks. Case studies will provide additional material to explain the use of these techniques. The tutorial will be structured into three main sections: We will first discuss the fundamentals of parallel programming and parallel machine architectures. Topics include message passing vs. shared memory, thread programming, a review of different SMP architectures, clustering techniques, PC architectures for personal workstations, and graphics hardware architectures. The second section builds on this foundation to describe key concepts and particular algorithms for parallel polygon and volume rendering. These concepts are supplemented with concrete parallel rendering implementationsItem Data Reconstruction and Visualization Techniques for Forensic Pathology(The Eurographics Association, 2006) Ehlert, Alexander; Salah, Zein; Bartz, Dirk; Beatriz Sousa Santos and Thomas Ertl and Ken JoyForensic pathology is largely concerned with the determination of the cause and manner of deaths after accidents, or other circumstances in criminal investigations. A major task in that process is the documentation of surface injuries, which is traditionally done by drawing sketches, photography, or more recently by photogrammetry to generate a three-dimensional digital lesion cartography of the body surface. In this paper, we describe a semi-automatic processing pipeline how data from 3D photogrammetry is combined and used to generate a visual surface representation of accident victims. In that course, a number of steps are performed to provide a high-quality interactive, point-based visualization of the acquired data, which can be used in a more routine way than previous forensic surface methods.Item Virtual Endoscopy in Research and Clinical Practice(Eurographics Association, 2003) Bartz, DirkVirtual endoscopy is among the most active topics in virtual medicine and medical imaging. It focuses on the virtual representation of minimally invasive procedures for training, planning, and diagnosis without an actual invasive intervention. In the past few years, virtual endoscopy modes have been transferred from research systems in virtually every commercial medical imaging software, but with a varying quality and flexibility. This report covers concepts used in current systems in research and products, and how they might be applied to daily practice in health-care. Specifically, I will start with an introduction into virtual endoscopy and the related medical field. This will also include typical scenarios of virtual endoscopy applications as they appear in clinical practice. This part will be followed by a discussion of the technical issues of virtual endoscopy and how are addressed in currently available systems. Among these issues are navigation through the respective body organ and the orientation aids for the users. Furthermore, I will highlight the different rendering techniques used and its impact on render speed and quality.