Short Presentations

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https://diglib.eg.org/handle/10.2312/225

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A Simple Validity Condition for B-Spline Hyperpatches
(Eurographics Association, 2001) Conde Rodriguez, Francisco de Asis; Torres Cantero, Juan Carlos
The 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.
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.
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.
Collision Detection for Continuously Deforming Bodies
(Eurographics Association, 2001) Larsson, Thomas; Akenine-Möller, Tomas
Fast 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.
A Microfacet Based Coupled Specular-Matte BRDF Model with Importance Sampling
(Eurographics Association, 2001) Kelemen, Csaba; Szirmay-Kalos, Laszlo
This 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.
Volumetric Model Repair for Virtual Reality Applications
(Eurographics Association, 2001) Kolb, Andreas; John, Lars
Repairing 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.
Deformable Terrain Generation for Real-time Strategy Game
(Eurographics Association, 2001) Davison, Christopher; Tang, Wen
In 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.
Animation of Facial Expressions by Physical Modeling
(Eurographics Association, 2001) Zhang, Yu; Prakash, Edmond C.; Sung, Eric
In 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.
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.
Fractal approximation of surfaces based on projected IFS attractors
(Eurographics Association, 2001) Guerin, Eric; Tosan, Eric; Baskurt, Atilla
A 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.
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.
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.
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.
Towards Rapid Reconstruction for Animated Ray Tracing
(Eurographics Association, 2001) Lext, Jonas; Akenine-Möller, Tomas
This 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.
3dml: A Language for 3D Interaction Techniques
(Eurographics Association, 2001) Figueroa, Pablo; Green, Mark; Hoover, H. James
We 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).
Space-Time Hierarchical Radiosity with Clustering and Higher-OrderWavelets
(Eurographics Association, 2001) Damez, Cyrille; Holzschuch, Nicolas; Sillion, Francois X.
We address in this paper the issue of computing global illumination solutions for animation sequences. The principal difficulties lie in the computational complexity of global illumination, emphasized by the movement of objects and the large number of frames to compute, as well as the potential for creating temporal discontinuities in the illumination, a particularly dangerous and noticeable artifact. We demonstrate how space-time hierarchical radiosity, i.e. the application to the time dimension of a hierarchical decomposition algorithm, can be effectively used to obtain smooth animations: first by proposing the integration of spatial clustering in a space-time hierarchy; second, by changing the wavelet basis used for the temporal dimension. The resulting algorithm is capable of creating time-dependent radiosity solutions efficiently.
Mayhem in Online Game and Virtual Environment Development
(Eurographics Association, 2001) Oliveira, Manuel Fradinho Duarte; Crowcroft, Jon; Slater, Mel
We present Mayhem, which is a prototype of a Massive Online Role Playing Game (MORPG), where novel research in the field of Virtual Environments (VEs) is combined with the requirements of online games. This results in a novel approach to develop VE systems. The paper analyses the building blocks of the underlying system supporting Mayhem. The system design is based on component frameworks, with the core infrastructure of the game revolving around the Java Adaptive Dynamic Environment (JADE). We discuss the main extension Modules supporting the system, such as the networking module and the data manager.
Approximated View Reconstruction Using Precomputed ID-Bitfields
(Eurographics Association, 2001) Meruvia Pastor, Oscar E.; Strothotte, Thomas
A technique is presented to construct arbitrary views of a model by using previously computed views. The technique is simple to implement, completely general for polygonal models and can be used within object hierarchies or scene graphs. During a preprocessing step images of a model are taken from different viewpoints. These images are saved using long bitfields (ID-bitfields) which encode the visibility information according to an array of the model’s primitives used as the base for the bitfield. These ID-bitfield encodings, together with the primitive array, are then used by a viewer which selects and joins them to provide an approximated (not conservative) reconstruction of the visible elements of the object for a new viewpoint. The technique implicitly performs occlusion culling, since a minimal set of visible polygons is the result of the reconstruction. Results show how interaction can be improved when working with high depth complexity models. Satisfactory reconstructions are achieved by taking as few as 25 images around an object. This paper suggests how the technique can be extended to other applications such as virtual walkthroughs and visualization of non-realistic images, and how graphics libraries and hardware could be enhanced by allowing the application to pass an ID-bitfield. Key words: view reconstruction, interactive display, visibility preprocessing, occlusion culling, polygon reduction.
Interactive 3D Modeling in the Inception Phase of Architectural Design
(Eurographics Association, 2001) de Vries, B.; Jessurun, A.J.; van Wijk, J.J.
In architectural design 3D modeling in the inception phase is up to now not supported in CAD. Moreover 3D modeling is still far from intuitive with the common interface techniques. This paper introduces a 3D modeling tool for architects, which is limited in its purposes but yet very powerful in its use. A cube is the basic drawing element to construct building masses. Modification of the design is achieved by dragging sets of cubes resulting in the creation or deletion of new cubes.
N-Adic Subdivision Schemes for Local Mesh Deformation
(Eurographics Association, 2001) Salomon, Gabriel; Leclerq, Antoine; Akkouche, Samir; Galin, E.
This paper presents an interpolating subdivision scheme based on an N-adic decomposition of the parameter space. This approach enables us to locally deform the surface according to a modification of the normals at the vertices of the control mesh. Experiments show that the N-adic decomposition provides a better control over the deformations, whereas a dyadic decomposition method often produces smoother surfaces.

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