Short Presentations

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

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Parametric Motion Blending through Wavelet Analysis
(Eurographics Association, 2001) Ahmed, Amr; Mokhtarian, Farzin; Hilton, Adrian
This paper shows how multiresolution blending can be employed with time-warping for realistic parametric motion generation from pre-stored motion data. The goal is to allow the animator to define the desired motion using its natural parameters such as speed. Generation of a realistic motion is achieved using pre-stored captured animations. Analysis has been carried out to investigate the relationship between the walking speed and blending factor to remove the burden of trial and errors from the animator. As a result, realistic walking motion with the speed specified by the user can be generated. This desired speed should be between the minimum and maximum speeds of the available motion data. Analysis to generalise these results to other motions are in progress. Generating the desired motion for different scaled avatars is also discussed.
Free-Form Deformation of Solid Models in CSR
(Eurographics Association, 2001) Hui, K. C.; Lai, C.F.
Existing free-form deformation (FFD) techniques deform an object by deforming the space enclosing the object. Points on the object are thus deformed relative to the undeformed space (or world space). The deformed object is visualized by sampling points on the object surfaces, or by approximating the object with a polyhedral model. This provides good visual effect for the deformed objects. However, the deformed solid is represented in terms of the lattice of the FFD and the undeformed solid. There is no precise explicit representation of the deformed object so that existing solid modeling techniques, such as Boolean operations, on the deformed object may not be applied. This paper is concerned with the techniques of applying free-form deformation on solid models represented by the Constructive Shell Representation (CSR). By applying free-form deformation on the surface points of the trunctets of a CSR object so that the vertices and the quadric patch polynomial of the trunctets are changed, the shape of the object can be modified. This technique can be used to deform globally smooth solid models or general solid models with sharp edges. The deformation can be applied either globally or locally. Techniques for the deformation are discussed in detail. Experiments are conducted and the results are also presented.
Game Based Interfaces
(Eurographics Association, 2001) Diener, Holger; Schumacher, Hagen
Complex menu and dialog structures prevent users from working intuitively with standard applications. In this paper, a new kind of user interface is suggested based on concepts of computer games. Defining a new structure for the functionality of an application will simplify users adjustment to new applications and will improve their everyday work. Usability tests based on eye tracking devices are described to verify the correctness of this game based interface approach. In addition, other game based concepts are introduced, which can be transferred to standard applications to improve the usability.
Approximated Phong Shading by using the Euler Method
(Eurographics Association, 2001) Hast, Anders; Barrera, Tony; Bengtsson, Ewert
After almost three decades and several improvements, Gouraud shading is still more often used for interactive computer graphics than Phong shading. One of the main reasons for this is of course that Phong shading is computationally more expensive. Quadratic polynomial approximation techniques like Bishop’s method could reduce the amount of computation in the inner loop to just the double of what is done in Gouraud shading. By using Euler’s method we get another quadratic polynomial approximation technique which is just as fast in the inner loop, but it will also give correct intensities on the edges, which we will not get with Bishop’s method. By computing the maximum difference over a scan line between Gouraud shading and the proposed method, we could decide if Gouraud will suffice. It is also shown that linearly interpolated normals are normalized by a symmetric function. This means that we could reduce the amount of square roots by the half in Phong shading.
An Improved Spacetime Ray Tracing System for the Visualization of Relativistic Effects
(Eurographics Association, 2001) Li, Jiang; Shum, Heung-Yeung; Peng, Qunsheng
Traditional ray tracing methods are based on Newton’s classical mechanics. They cannot reproduce the visual phenomena of high-speed motion. In this paper, we develop an improved spacetime ray tracing system, which provides a framework for the visualization of spacetime relativistic effects. The system consists of three major components. First, a transformation platform is established to process the transformations of spacetime coordinates and velocities between different scene elements. This enables the independent scene modeling at different reference frames. Second, a number of spacetime scene data structures are constructed to encapsulate conventional scene elements such as objects, light sources, and cameras. Third, a medium information stack is designed to record in which medium the tracing ray is traveling. This enables the accurate calculations of light speeds, which are critical in the visualization of relativistic effects. Experiments are performed when synthetic objects, light sources and cameras are moving at high speeds relative to each other. In addition to conventional relativistic effects, we discover in our system a number of novel visual effects such as multiple transmissions, omnidirectional reflection, and delayed appearance of shadows.
Scalable Impressionist Rendering
(Eurographics Association, 2001) Atencia, A.; Bourdin, Jean-Jacques; Boyer, V.; Pissard, T.; Sobczyk, D.
The painted impressionist technique produces scale based effects: the far range vision is almost realistic while the close vision is blurred. In NPR, Impressionist Renderers are mainly based on a medium range vision. A very accurate scalable impressionist effect has been implemented and improves both close and far range vision.
Artist Driven Expressive Graphics
(Eurographics Association, 2001) Mason, Kaye; Carpendale, Sheelagh
Current methods in non-photorealistic graphics can place a heavy emphasis on the algorithm, as opposed to the artist. In this paper, we analyse these trends, and present a conceptual framework for putting control back in the hands of the artist. Combining ideas from non-photorealistic graphics and artificial intelligence, we present new methods of supporting alternative artistic styles. Details of our implementation of this model are described, as well as methods for interaction. Finally, we create a simulation under this framework, and show preliminary results.
Metaprogramming for the Generation of Nonparametric Curves
(Eurographics Association, 2001) Boyer, Vincent
One of the most important functions of paintboxes is drawing curves. These primitives have been programmed and the user can never add a new program which computes the discrete points of a given function. Using metaprogramming and the Jordan’s method, our program CAPC automatically generates, for a given function, a new program which computes the discrete points for this function and adds it to our paintbox tool.
Managing Gigabyte Virtual EnvironmentWalkthrough
(Eurographics Association, 2001) Shou, Lidan; Chionh, Jason; Huang, Zhiyong; Ruan, Yixin; Tan, Kian-Lee
In this paper, we study the problem of interactive walkthrough of a large virtual environment (VE) where the data representing 3D virtual objects can not reside completely in the main memory. We tap into the wealth of techniques (indexing, caching, prefetching) that have been widely used by the database community, and investigate how walkthrough semantics can be integrated into these techniques. In our approach, the VE data in the main memory are dynamically managed such that only those of the relevant 3D objects pertaining to the current user’s viewpoint are loaded into the main memory. The objects in the VE are spatially indexed by a spatial index structure (R-tree) as opposed to splitting the VE into smaller rigid-sized grids. Queries are issued to the R-tree to retrieve only the relevant objects. We propose a novel complement search algorithm to improve the standard search. In addition, we propose a cache replacement policy that considers the access pattern of walkthrough to facilitate effective memory management; and a prediction algorithm that computes the next likely position of the user in order to prefetch data. We implemented a prototype walkthrough system and evaluated it on a 1 GB synthetic dataset of a cityscape. Our results show that the proposed techniques deployed can lead to a high constant frame rate for the walkthrough.
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.
Adaptive Progressive Vertex Tracing for Interactive Reflections
(Eurographics Association, 2001) Ullmann, Thomas; Schmidt, Alexander; Beier, Daniel; Bruderlin, Beat
This paper presents an approach for real-time rendering of physically accurate reflection effects in virtual environments. We apply a hybrid rendering of an OpenGL-generated scene, blended with correct reflection characteristics of selected scene objects. The core of the approach consists of a special type of ray tracing, the so-called vertex tracing. Real-time performance, even for complex CAD scenes, is achieved by progressive adaptive refinement, (derived from the geometry in object space) as well as by parallelization of the algorithm. A mesh-based load balancing yields a uniform distribution of the computing load in a heterogeneous network with resources with widely varying performance. The performance of the overall system is demonstrated using a truck interior in a Virtual Reality simulator.
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.
Improved Rendering with Dégradé
(Eurographics Association, 2001) Boyer, Vincent; Sobczyk, Dominique; Bourdin, Jean-Jacques
In most paintboxes drawing (and filling) the picture and render the picture are two different steps and tools. Dégradé presents an efficient filling rendering tool: an efficient collection of effect filling. In Dégradé the renderer is included in the drawing process. This method enhance the renderer possibilities and the graphic designer work.
Post-rendering Composition for 3D Scenes
(Eurographics Association, 2001) Grimm, Cindy
In traditional art a painter displays a 3D scene on a 2D image plane in a manner that is aesthetically pleasing. The arrangement of objects and colors is called composition and is the subject of many art books and classes. While a painter may use perspective to create depth in a scene they may also alter the perspective and color, either subtly or dramatically, to influence the focus of viewer and the effect of the image. To date, traditional 3D graphics packages have largely concentrated on modeling, textures, and lighting to create images and provide few tools for altering the composition post-rendering. In this paper we present several simple techniques for creating images with non-standard perspective and color using standard 3D rendering packages. The scene is modeled in 3D but each object has its own camera, color balance, and image size, allowing the user to alter the composition after the 3D rendering step. The purpose of this paper is not to present a complete composition system but rather to illustrate the potential of compositionbased tools.
Improvement of the printing model in multi-colored and multi-woodblock virtual printing
(Eurographics Association, 2001) Mizuno, Shinji; Ushida, Akihide; Okada, Minoru; Toriwaki, Jun-ichiro; Yamamoto, Shinji
In this paper, we propose a physically based model for the printing process in the virtual woodblock printing for improvement of printing quality. Virtual printing is a simulation of real printing using “woodblocks”, “a paper sheet”, “a baren (Japanese squeegee)”, and “inks” in a virtual 3D space. A print is synthesized by an interaction among them, and it is very important to study physical properties and behaviors of the virtual items. We focus on the property and the behavior of ink and study a variety of effects due to the degree of moisture of the ink.
Local Versus Global Triangulations
(Eurographics Association, 2001) Linsen, Lars; Prautzsch, Hartmut
Free form surfaces are commonly represented by triangular or quadrilateral meshes. Often these meshes are obtained from unorganized point sets sampled from some object’s surface. We show that local rather than global triangulations of point sets are equally well suited for object representations and that the local triangulations proposed in this paper may even lead to fast triangulation routines.
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 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.
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.
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.

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