EG2000

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https://diglib.eg.org/handle/10.2312/218

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The modelling of growing natural forms
(Eurographics Association, 2000) Jones, Huw; Kaandorp, Jaap
The tutorial introduces a variety of ways of modelling branching biological structures. Methods for generating plant like images, such as Diffusion Limited Aggregation and Iterated Function Systems are briefly discussed. The main concentration is on two methods that can be used to model the growth of such structures. The powerful Lsystems method gains explanatory power by use of parameters, context and environmental sensitivity, enabling natural features such as leaf drop, self-pruning and self-seeding. The method of Kaandorp for modelling marine sessile organisms such as sponges and corals, in which geometric features are “grown” directly, is compared for veracity with observed organisms in different physical environments.
An Image Processing Approach to Detection of Ridges and Ravines on Polygonal Surfaces
(Eurographics Association, 2000) Belyaev, Alexander; Ohtake, Yutaka
Surface creases, ridges and ravines, provide us with important information about the shapes of 3D objects and can be intuitively defined as curves on a surface along which the surface bends sharply. Exploring similarity between edges of 2D grey-scale images and curvature extrema of 3D shapes and generalizing a basic edge detection approach to triangular meshes, we develop a method for detection of ridges and ravines on a smooth surface approximated by a triangular mesh. We also sketch three potential applications of our approach: mesh fairness evaluation, improving mesh decimation techniques, and simulating artistic pen-and-ink drawings of 3D objects.
Visualizing Stars and Emission Nebulas
(Eurographics Association, 2000) Nadeau, David R.; Genetti, Jon D.; Napear, Steve; Pailthorpe, Bernard; Emmart, Carter; Wesselak, Erik; Davidson, Dennis
We describe star and nebula visualization techniques used to create a 3D volumetric visualization of the Orion Nebula. The nebula’s ionization layer is modeled first as a surface model, derived from infrared and visible light observations. The surface model is imported into a volume scene graph-based visualization system that uses procedural volume modeling to simulate the nebula’s emissive gas layers. Additional scene graphs model proplyds and shock fronts within the nebula. Stars are rendered using Gaussian spots that are attenuated with distance. Finally, eighty-six separate volumes are voxelized from these scene graphs, then simultaneously volume rendered.
Discrete Analysis for Antialiased Lines
(Eurographics Association, 2000) Boyer, V.; Bourdin, J. J.
This paper presents a new fast and smooth antialiasing technique. Drawing straight line is the graphic tool’s main primitive. Previous antialiasing techniques improve smoothness but slow down computation.
The 3D Model Acquisition Pipeline
(Eurographics Association, 2000) Bernardini, Fausto; Rushmeier, Holly
Three-dimensional image acquisition systems are rapidly becoming more affordable, especially systems based on commodity electronic cameras. At the same time, personal computers with graphics hardware capable of displaying complex 3D models are also becoming inexpensive enough to be available to a large population. As a result, there is potentially an opportunity to consider new virtual reality applications as diverse as cultural heritage and retail sales that will allow people to view realistic 3D objects on home computers. Although there are many physical techniques for acquiring 3D data – including laser scanners, structured light and time-of-flight – there is a basic pipeline of operations for taking the acquired data and producing a usable numerical model. We look at the fundamental problems of range image registration, line-of-sight errors, mesh integration, surface detail and color, and texture mapping. In the area of registration we consider both the problems of finding an initial global alignment using manual and automatic means, and refining this alignment with variations of the Iterative Closest Point methods. To account for scanner light-of-sight errors we compare averaging and conformance approaches. In the area of mesh integration, that is finding a single mesh joining the data from all scans, we compare various methods for computing interpolating and approximating surfaces. We then look at various ways in which surface properties such as color (more properly, spectral reflectance) can be extracted from acquired imagery. Finally, we examine techniques for a producing a final model representation that can be efficiently rendered using graphics hardware.
Towards Communicating Agents and Avatars in Virtual Worlds
(Eurographics Association, 2000) Nijholt, Anton; Hondorp, Hendri
We report about ongoing research in a virtual reality environment where visitors can interact with agents that help them to obtain information, to perform certain transactions and to collaborate with them in order to get some tasks done. In addition, in a multi-user version of the system visitors can chat with each other. Our environment is a laboratory for research and for experiments with users interacting with agents in multimodal ways, referring to visualized information and making use of knowledge possessed by domain agents, but also by agents that represent other visitors of this environment. We discuss standards that are under development for designing such environments. Our environment models a local theatre in our hometown. We discuss our attempts to let this environment evolve into a theatre community where we do not only have goal-directed visitors buying tickets, but also visitors that that are not yet sure whether they want to buy or just want information or visitors who just want to look around, talk with others, etc. It is shown that we need a multi-user and multi-agent environment to realize our goals and that we need to have a unifying framework in order to be able to introduce and maintain different agents and user avatars with different abilities, including intellectual, interaction and animation abilities.
Geometric Signal Processing on Polygonal Meshes
(Eurographics Association, 2000) Taubin, G.
Very large polygonal models, which are used in more and more graphics applications today, are routinely generated by a variety of methods such as surface reconstruction algorithms from 3D scanned data, isosurface construction algorithms from volumetric data, and photogrametric methods from aerial photography. In this report we provide an overview of several closely related methods developed during the last few yers, to smooth, denoise, edit, compress, transmit, and animate very large polygonal models.
Visual Perception in Realistic Image Synthesis
(Eurographics Association, 2000) McNamara, A.; Chalmers, A.; Trocianko, T.
Realism is often a primary goal in computer graphics imagery, we strive to create images that are perceptually indistinguishable from an actual scene. Rendering systems can now closely approximate the physical distribution of light in an environment. However, physical accuracy does not guarantee that the displayed images will have authentic visual appearance. In recent years the emphasis in realistic image synthesis has begun to shift from the simulation of light in an environment to images that look as real as the physical environment they portray. In other words the computer image should be not only physically correct but also perceptually equivalent to the scene it represents. This implies aspects of the Human Visual System (HVS) must be considered if realism is required. Visual perception is employed in many different guises in graphics to achieve authenticity. Certain aspects of the human visual system must be considered to identify the perceptual effects that a realistic rendering system must achieve in order to effectively reproduce a similar visual response to a real scene. This state-of-the-art report outlines the manner in which knowledge about visual perception is increasingly appearing in state-of-the-art realistic image synthesis. This STAR is organised into three sections, each exploring the use of perception in realistic image synthesis, each with slightly different emphasis and application. First, perception driven rendering algorithms are described, these algorithms focus on embedding models of the Human Visual System (HVS) directly into global illumination computations in order to improve their efficiency. Then perception based image quality metrics, which aim to compare images on a perceptual rather than physical basis are presented. These metrics can be used to evaluate, validate and compare imagery. Finally, Tone Reproduction Operators, which attempt to map the vast range of computed radiance values to the limited range of display values, are discussed.
Virtual Humans: Ten Problems Still Not Completely Solved
(Eurographics Association, 2000) Thalmann, Daniel
During the 1980s, the academic establishment paid only scant attention to research on the animation of virtual humans. Today, however, almost every graphics journal, popular magazine, or newspaper devotes some space to Virtual Humans and their applications. But, there are still a lot of problems to generate believable Virtual Humans. The purpose of this paper is to identify ten main problems to solve to create and animate believable Virtual Humans.
Robust Polygons Clipping to Model Complex Objects
(Eurographics Association, 2000) Segura, Rafael J.; Feito, Francisco R.
One of the most important problems to solve in Solids Modelling is computing the boolean operations for solids (union, intersection and difference). In order to implement these three operations an algorithm to compute the intersection between faces is needed (polygons clipping). In the case of solids with planar faces there are many solutions, although most of them are valid only when the faces are convex. In this paper we present an algorithm to determine the intersection between polygons of any nature (concave or convex, manifol or non-manifold, with or without holes, etc.) based on the idea of simplicial coverings proposed by Feito 11. One of the advantages of this approach is the robustness of algorithms, since decompositions or complex operations that may alter the results obtained are not avoided. A very interesting application of this algorithm is the modelling of complex solids with this type of polygons as faces.
Principles of Computer Graphics: the experience of a class A user
(Eurographics Association, 2000) Cailliau, Robert
Computer graphics has gone a long way from the early days in the 50’s and 60’s. Today we have the web, and it’s all visual that is the fashion. What does an unsuspecting user of computers, who is not a specialist, actually experience? Where are we when we leave the 3D interactive shooting game world and we want to do some simple things?
Collaboration in VEs − fact or fiction?
(Eurographics Association, 2000) Hubbold, Roger J.
The growth of the Internet, and company intranets, fuelled by the promise of sophisticated on−line services, has raised expectations of rich collaborative virtual environments, in which humans can indulge in cooperative problem solving. Pioneering demonstrations, such as the work of NASA on rehearsing maintenance tasks for the Hubble telescope, and recent moves into on−line multi−user gaming, have given us a glimpse of what may be possible in a restricted context. And yet, for most users the reality is somewhat different. Interaction in virtual environments is hard enough with only a single user. Add to this the problems of multiple users, collaborating over a network, and we still seem some way from having a really useful, or even usable, tool. The problems span technology (faster, lower latency networks will help, but will not, by themselves solve the problem), software architectures (just how do we ensure a coherent view of a shared environment for multiple users?), to psychology and human factors (we need experiments to quantify how well things work). Above all, how do we come up with solutions which not only work but are accessible to, and usable by, ordinary programmers and end−users? In this talk I will explore some of these problems and describe our own attempts at addressing them.
An Accurate Illumination Model for Objects Coated with Multilayer Films
(Eurographics Association, 2000) Hirayama, H.; Kaneda, K.; Yamashita, H.; Monden, Y.
This paper proposes an accurate illumination model for rendering objects coated with multilayer films. Optical phenomenaof multilayer films are caused by reflection, refraction, interference, and absorption of light inside each layer of multiple films, and these physical phenomena are complicatedly related with each other. The proposed method calculates composite reflectance and transmittance of multilayer films, taking into account all the physical phenomena described above, and visualizes the optical phenomena caused by the multilayer films accurately. The illumination model proposed in the paper can handle both smooth surface and locally smooth rough surfaces. Several examples of objects coated with various kinds of films demonstrate the usefulness of the proposed method.
Combining finite element deformation with cutting for surgery simulations
(Eurographics Association, 2000) Nienhuys, Han-Wen; van der Stappen, A. Frank
Interactive surgery simulations have conflicting requirements of speed and accuracy. In this paper we show how to combine a relatively accurate deformation model—the Finite Element (FE) method—and interactive cutting without requiring expensive matrix updates or precomputation. Our approach uses an iterative algorithm for an interactive linear FE deformation simulation. The iterative process requires no global precomputation, so runtime changes of the mesh, i.e. cuts, can be simulated efficiently. Cuts are performed along faces of the mesh; this prevents growth of the mesh. We present a provably correct method for changing the mesh topology, and a satisfactory heuristic for determining along which faces to perform cuts. The incision surface will be jagged; this problem is a subject of current research.
A Novel Image-Based Rendering System With A Longitudinally Aligned Camera Array
(Eurographics Association, 2000) Li, Jiang; Zhou, Kun; Wang, Yong; Shum, Heung-Yeung
Selecting Effective Occluders for Visibility Culling
(Eurographics Association, 2000) Koltun, Vladlen; Cohen-Or, Daniel
This paper deals with the problem of identifying effective occluders for visibility culling. The solid-angle metric is commonly used for measuring the potential significance of occluders from a single viewpoint. In this paper, we show that it does not extend properly to from-region occlusion calculations. We propose to measure the effectiveness of an occluder by means of the size of its umbra. We first present an analytic object-space algorithm to accurately compute this measure. We then define an approximation which reflects the effectiveness of an occluder, and introduce a hardware-assisted algorithm to rapidly compute it.
Geometric Modeling Based on Polygonal Meshesv
(Eurographics Association, 2000) Kobbelt, Leif P.; Bischoff, Stephan; Botsch, Mario; Kähler, Kolja; Rössl, Christian; Schneider, Robert; Vorsatz, Jens
While traditional computer aided design (CAD) is mainly based on piecewise polynomial surface representations, the recent advances in the efficient handling of polygonal meshes have made available a set of powerful techniques which enable sophisticated modeling operations on freeform shapes. In this tutorial we are going to give a detailed introduction into the various techniques that have been proposed over the last years. Those techniques address important issues such as surface generation from discrete samples (e.g. laser scans) or from control meshes (ab initio design); complexity control by adjusting the level of detail of a given 3D-model to the current application or to the available hardware resources; advanced mesh optimization techniques that are based on the numerical simulation of physical material (e.g. membranes or thin plates) and finally the generation and modification of hierarchical representations which enable sophisticated multiresolution modeling functionality.
Shadow Computation: A Unified Perspective
(Eurographics Association, 2000) Ghali, S.; Fiume, E.; Seidel, H.-P.
Methods for solving shadow problems by solving instances of visibility problems have long been known and exploited. There are, however, other potent uses of such a reduction of shadow problems, several of which we explore in this paper. Specifically, we describe algorithms that use a resolution–independent, or object–space, visibility structure for the computation of object–space shadows under point, linear, and area light sources. The connection between object–space visibility and shadow computation is well–known in computer graphics. We show how that fundamental observation can be recast and generalized within an object–space visibility structure. The edges in such a structure contain exactly the information needed to determine shadow edges under a point light source. Also, the locations along a linear or an area light source at which visibility changes (termed critical points and critical lines) provide the necessary information for computing shadow edges resulting from linear and area light sources. Not only are instances of all shadow problems thus reduced to visibility problems, but instances of shadow problems under linear and area light sources are also reduced to instances of shadow generation under point and linear light sources, respectively.
Automatic Fitting of Digitised Contours at Multiple Scales through Curvature Scale Space
(Eurographics Association, 2000) Mokhtarian, Farzin; Ung, Yoke Khim
The Curvature Scale Space (CSS) technique has been used in conjunction with Hermite curves for automatic fitting of digitised contours at multiple scales. CSS is a powerful contour shape descriptor which is expected to be in the MPEG-7 standard. A parametric representation of the input contour is convolved with Gaussian functions in order to obtain multi-scale descriptions of the contour. Curvature can be computed directly at each point of the smoothed contours. As a result, a set of curvature zero-crossing points can be recovered from each smoothed contour. Hermite curves were used since each Hermite curve is defined by two endpoints and the tangent vectors at those points. No points external to the input contour are required for Hermite curves. Hermite endpoints are defined as consecutive curvature zero-crossing points extracted at multiple scales using the CSS method. Hermite tangent vectors can also be determined using the CSS technique. The only data stored are the endpoints and the tangent vectors needed by the Hermite curves in order to arrive at an approximate reconstruction of the original contour. Approximation Error and Compression Ratio are computed at each scale. The graph of compression ratio as a function of approximation error is smoothed to remove noise and small fluctuations. The bending point of that function is then defined as the largest maximum of its second derivative. The bending point can be considered as the boundary between the mostly vertical and the mostly horizontal segments of the graph. It can be used for automatic selection of an optimal scale.
MeshSweeper: From Closest Point to Hausdorff Distance Between Meshes
(Eurographics Association, 2000) Gueziec, A.
We introduce a new algorithm for computing the distance from a point to an arbitrary polygonal mesh. Our algorithm uses a multi-resolution hierarchy of bounding volumes generated by geometric simplification. Our algorithm is dynamic, exploiting coherence between subsequent queries using a priority process (without caching the closest point), and achieving constant time queries in some cases. The method also applies to a mesh that deforms nonrigidly. Achieving from about 500 to several thousand queries per second for a complex polygonal shape on a PC, our method has applications both for interactive and photo-realistic graphics. In particular, we study in this paper the application to computing the Hausdorff distance between two polygonal shapes, with an arbitrary precision.

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