EG2001
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Item A Simple Validity Condition for B-Spline Hyperpatches(Eurographics Association, 2001) Conde Rodriguez, Francisco de Asis; Torres Cantero, Juan CarlosThe use of hyperpatches as a method for solid modelling has a problem: the validity of the model is not guaranteed. The problem of ensuring the validity of hyperpatch representations of solids is discussed in this work, and a validity condition for cubic uniform b-spline hyperpatches is presented. Our validity condition is based on comparisons among points, and it is robust and easy to implement.Item Proxy Simulations for Efficient Dynamics(Eurographics Association, 2001) Chenney, Stephen; Arikan, Okan; Forsyth, D. A.Proxy simulations reduce the cost of simulation in large virtual worlds, such as those used in training simulations or computer games. A proxy takes the place of an accurate simulation for objects that are out of view, while the accurate model continues to manage visible objects. A proxy must ensure that objects enter the view at reasonable times throughout the simulation and in states that reffect their time spent out of view. The quality of a proxy simulation is measured by how well it maintains reasonable behaviors, where the deffinition of reasonable depends on the environment and its application. We present two examples of proxy simulations based on discrete event models: one for city traffic simulation and another for multi-agent path planning and motion. For these examples, we demonstrate dynamics computation speedups of over two orders of magnitude as the environments grow in size and complexity.Item Web 2D Graphics: State-of-the-Art(Eurographics Association, 2001) Duce, David; Herman, Ivan; Hopgood, BobThe early browsers for the Web were predominantly aimed at retrieval of textual information. Tim Berners-Lee's original browser for the NeXT computer did allow images to be viewed but they popped up in a separate window and were not an integral part of the Web page. In January 1993, the Mosaic browser was released by NCSA. The browser was simple to download and, by the Autumn of 1993, was available for X workstations, PCs and the Mac. From 50 Web servers at the start of 1993, Web traffic had risen to 1% of internet traffic by October and 2.5% by the end of the year. About a million downloads of the Mosaic browser took place that year. In February of 1993, Mark Andreessen proposed theelement as an extension to Mosaic's HTML to provide a way of adding images to Web pages. In 1994, Dave Raggett developed an X-browser that allowed text to flow around images and tables and from then on images were an accepted part of the Web page. Web pages became glossier and the enormous growth of the Web started [1] [2]. Organisations could customise their home pages with the company logo. Maps, albeit images, could be added to show how to reach the organisation. Its products could be displayed on the Web. Eventually, the Web would become a major commercial outlet.
Item A Visualization System for the Clinical Evaluation of Cerebral Aneurysms from MRA Data(Eurographics Association, 2001) Perrin, James S.; Lacey, A.; Laitt, R.; Jackson, A.; John, Nigel W.This paper details a work-in-progress application under development as part of a clinical visualization project. The software has been designed to meet the specific needs of interventional neuro-radiologists evaluating the suitability of intracranial aneurysms for endovascular coiling and also when planning the procedure. Providing rapid (real-time) interaction with high resolution iso-surfaces derived from Time-of Flight (ToF) Magnetic Resonance Angiography (MRA) data will enable the clinician to quickly assess the ability of the aneurysm to accept a coil, with greater reliability than exisiting, 2D film techniques. Simulating the interface of the C-arm angiography system, used during the procedure, allows the clinician to evaluate various surgical strategies, potentially reducing procedure times and therefore patient radiation dosage. The first release of the software is currently under-going clinical evaluation.Item Collision Detection for Continuously Deforming Bodies(Eurographics Association, 2001) Larsson, Thomas; Akenine-Möller, TomasFast and accurate collision detection between geometric bodies is essential in application areas like virtual reality, animation, simulation, games and robotics. In this work, we address the collision detection problem in applications where deformable bodies are used, which change their overall shape every time step of the simulation. We propose and evaluate suitable bounding volume trees for deforming bodies that can be pre-built and then updated very efficiently during simulation. Several heuristics for updating the trees due to deformations are compared to each other. By combining a top-down and a bottom-up update strategy into a hybrid tree update method, promising results were achieved. Experiments show that our approach is four to five times faster than a previously leading method.Item Item A Microfacet Based Coupled Specular-Matte BRDF Model with Importance Sampling(Eurographics Association, 2001) Kelemen, Csaba; Szirmay-Kalos, LaszloThis paper presents a BRDF model based on the analysis of the photon collisions with the microfacets of the surface. The new model is not only physically plausible, i.e. symmetric and energy conserving, but provides other important features of real materials, including the off-specular peak and the mirroring limit case. Using theoretical considerations the reflected light is broken down to a specular component representing single reflections and a matte component accounting for multiple reflections and re-emissions of previously absorbed photons. Unlike most of the previous models, the proportion of the matte and specular components is not constant but varies with the viewing angle. In order to keep the resulting formulae simple, several approximations are made, which are quite accurate but allow for tabulation, fast calculation and even for accurate importance sampling.Item Volumetric Model Repair for Virtual Reality Applications(Eurographics Association, 2001) Kolb, Andreas; John, LarsRepairing Virtual Reality (VR) models is a challenge for productive applications. This paper describes a fast implementation of Nooruddin and Turk’s ray-stabbing method 14 based on standard graphics hardware. Raystabbing is used to convert a polygonal model into a volume model (also called voxelization). The volume model is back-converted into a polygonal model using the marching cubes (MC) algorithm 12 and the QSlim algorithm 7 for reducing the extracted polygon model. The overall process yields a properly closed polygonal model with no visual unimportant features like nested or overlapping geometries or unwanted cracks. The voxelization process is the key part of the reparation process. We discuss implementation details and essential problems of ray-stabbing not addressed by Nooruddin and Turk 14.We focus on the generation of the volume model utilizing OpenGL hardware support. The current implementation is a snapshot of an ongoing work at EADS Airbus, Europes leading commercial aircraft company. The final goal is a fast model repair and reduction workflow for generating VR-models and various levels of detail. Problems erase from the fact, that the polygonalization of the volume model using the MC-algorithm generates a far too fine tessellated model which then has to be reduced again. We also discuss possible approaches to overcome this drawback.Item Deformable Terrain Generation for Real-time Strategy Game(Eurographics Association, 2001) Davison, Christopher; Tang, WenIn this paper, we present a system that has the ability to deform terrain for Real-time Strategy Game with general PC hardware specifications. Various effects could be simulated in real-time such as raising and lowering the ground, creating a large chasm, or levelling the terrain. Effects such as ordering a unit to fire that then destroys part of a mountain could also be replicated. We present our implementations and techniques in using terrain deformation algorithms, Real-time Optimally Adapting Meshes, texture design and terrain generations. An analysis of the speed and memory usage of the system with respect to different PC hardware systems is also presented.Item Animation of Facial Expressions by Physical Modeling(Eurographics Association, 2001) Zhang, Yu; Prakash, Edmond C.; Sung, EricIn this paper, we propose a physically-based 3D dynamic facial model based on anatomical knowledge for realistic facial expression animation. The facial model incorporates a physically-based approximation to facial skin tissue and a set of anatomically-motivated facial muscle actuators. The tissue model has multilayered mass-spring structure which approximates different types of facial tissue. Two kinds of biphasic springs, structural springs and shear springs, are included in our model to simulate nonlinear elastic behavior of the skin. Facial muscle models are presented to emulate facial muscle contraction. In the muscle model, two factors, the muscle force scaling factor and muscle strength factor provide us macro and micro control of the muscle influence respectively. Based on the facial anatomy, these contractile muscles are inserted at anatomically correct position within the dynamic skin model. Lagrangian mechanics governs the dynamics, dictating the deformation of facial surface in response to muscle forces. The dynamic facial animation algorithm runs at interactive rate with continuous 3D display on a graphics workstation.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 Piecewise Constant Conic Sections for Accelerated Volume Density Rendering(Eurographics Association, 2001) Hougs, Roland B.; Day, A. M.In order to accelerate the rendering of volumetric shadows, we propose a new technique which builds sets of conic volumes to approximate the shape of shadows in a participating medium. The novelty of our approach is notably the construction of the cone-sets, which are built with no knowledge of the underlying geometry of the scene. Instead, information collected during the construction of a global photon map is used to derive an estimate of the outline of the shadows in three dimensions. This information is then used in several different ways to speed up the rendering pass. The method shares many of the advantages proposed by photon maps such as viewpoint independence and decoupling from the geometry of the scene.Item Fractal approximation of surfaces based on projected IFS attractors(Eurographics Association, 2001) Guerin, Eric; Tosan, Eric; Baskurt, AtillaA method for approximating smooth or rough surfaces defined in R3 is introduced. A fractal model called projected IFS model allows the extension of the iteration space to a barycentric space Rn2 by enriching the classical IFS model with a set of control points (m2 points). This flexible model has good fitting properties for recovering surfaces. The input for the model is single viewpoint range data defined on a fixed grid and also 2D grey-level images considered as surfaces. The model recovery is formulated as a non-linear fitting problem and resolved using a modified LEVENBERG-MARQUARDT minimization method. During the iterative fitting algorithm, all the parameters of the projected IFS model are adjusted simultaneously in order to minimize the overall distance between the models surface and the original data. The final model is very compact and gives satisfactory results on synthetic range data and real geological surfaces. The main applications are surface modeling, shape description and geometric surface compression.Item Data Mining and Visualization of High Dimensional Datasets(Eurographics Association, 2001) Inselberg, Alfred-Item Redirected Walking(Eurographics Association, 2001) Razzaque, Sharif; Kohn, Zachariah; Whitton, Mary C.Redirected Walking, a new interactive locomotion technique for virtual environments (VEs), captures the benefits of real walking while extending the possible size of the VE. Real walking, although natural and producing a high subjective sense of presence, limits virtual environments to the size of the tracked space. Redirected Walking addresses this limitation by interactively and imperceptibly rotating the virtual scene about the user. The rotation causes the user to walk continually toward the furthest wall of the lab without noticing the rotation. We implemented the technique using stereo graphics and 3D spatialized audio. Observations during a pilot study suggest that the technique works: Redirected Walking causes people to change their real walking direction without noticing it, allows for larger VEs, and does not induce appreciable simulator sickness.Item Animating cuts with on-the-fly re-meshing(Eurographics Association, 2001) Ganovelli, Fabio; O’Sullivan, C.The problem of defining a model for deformable objects which allows the user to perform cuts is still open. Generally speaking, the reason is that such a task affects the connectivity and the topology of the mesh, while the assumption that they never change is the basis of most algorithms for both computation of deformation and collision detection. The drawback of approaching this problem as one of cutting based on re-meshing, is that the mesh exhibits a higher density where it has been cut than elsewhere. This paper proposes an on-the-fly tetrahedral simplification scheme to cope with such a fragmentation problem.Item Inhabited Virtual Heritage(Eurographics Association, 2001) Magnenat-Thalmann, Nadia; Chalmers, Alan; Thalmann, DanielTwo techniques depending on the interest – accuracy and precision of the obtained object model shapes, • CAD systems, medical application. – visual realism and speed for animation of the reconstructed models, • internet applications • Virtual Reality applications.Item Constructive Hypervolume Textures(Eurographics Association, 2001) Schmitt, B.; Pasko, A.; Adzhiev, V.; Schlick, C.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 in 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.Item Towards Rapid Reconstruction for Animated Ray Tracing(Eurographics Association, 2001) Lext, Jonas; Akenine-Möller, TomasThis article discusses methods for avoiding that the reconstruction of the acceleration data structure becomes a bottleneck in animated or interactive ray tracing. Situations in which this could occur include trying to increase the frame rate by parallelization of the ray tracing phase or by techniques such as frameless rendering. Specifically, we explore a method for avoiding unnecessary reconstruction in rigid-body animated scenes. The method builds a hierarchy of oriented bounding boxes containing recursive grids by applying these to the rigid bodies found in different transforms in the scene graph. The oriented bounding boxes containing gridded objects are then kept intact during the complete animation. Before performing intersection tests, rays are transformed to the local coordinate system of an oriented bounding box. Using this technique, the reconstruction of the data structure can be performed an order of magnitude faster as compared to using a recursive grid that has to be rebuilt completely between each frame.Item 3dml: A Language for 3D Interaction Techniques(Eurographics Association, 2001) Figueroa, Pablo; Green, Mark; Hoover, H. JamesWe present 3dml, a markup language for 3D interaction techniques and virtual environment applications that involve non-traditional devices. 3dml has two main purposes: readability and rapid development. Designers can read 3dml-based representations of 3D interaction techniques, compare them, and understand them. 3dml can also be used as a front end for any VR toolkit, so designerswithout programming skills can create VR applications as 3dml documents that plug together interaction techniques, VR objects, and devices. This paper focuses on the language features and presentation scheme designed in our website (http://www.cs.ualberta.ca/~pfiguero/3dml).