Volume 16 (1997)

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    Implicit Representations of Rough Surfaces
    (Blackwell Publishers Ltd and the Eurographics Association, 1997) Hart, John C.
    Implicit surface techniques provide useful tools for modeling and rendering smooth surfaces. Deriving implicit formulations for fractal representations extends the scope of implicit surface techniques to rough surfaces. Linear fractals modeled by recurrent iterated function systems may be defined implicitly using either geometric distance or escape time. Random fractals modeled using Perlinâ s noise function are already defined implicitly when described as "hypertexture."Deriving new implicit formulae is only the first step. Unlike their smooth counterparts, rough implicit surfaces require special rendering techniques that do not rely on continuous differentiation of the defining function. Preliminary experiments applying blending operations to rough surfaces have succeeded in an initial attempt to overcome current challenges in natural modeling. The grafting of a stem onto the base of a linear fractal leaf continuously blends smooth detail into rough detail. The blend of two textured cylinders interpolates geometric bark across branching points in a tree.
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    Selective Pixel Transmission for Navigating in Remote Virtual Environments
    (Blackwell Publishers Ltd and the Eurographics Association, 1997) Mann, Yair; Cohen-Or, Daniel
    This paper presents a technique to improve the performance of a walkthrough in remote virtual environments, where a scene is rendered jointly by the server and the client, in order to reduce the network requirements as much as possible. The client generates novel views by extrapolating a reference view based on the locally available geometric model, while the server transmits data necessary to prevent an accumulation of errors. Within this concept, we show that by transmitting only a selected subset of pixels, the quality of the extrapolated views can be improved while requiring less bandwidth. We focus on the selection process in which the visibility gaps between the reference view and novel view are detected, packed and transmitted compressed to the client.
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    Modeling and Rendering of the Atmosphere Using Mie-Scattering
    (Blackwell Publishers Ltd and the Eurographics Association, 1997) Jackel, D.; Walter, B.
    This paper presents a method for rendering of the atmosphere by means of Mie-scattering. The method is based on a concentric atmospheric model, which is divided into four submodels: for clear air, aerosol, ozone, and rain. In order to simulate and visualize the various atmospheric effects, each of these submodels can be parameterized by the user as desired. The process of rendering an outdoor scene requires an enormous amount of computing power. In order to make this method suitable for efficient implementation, some simplifications and approximations are discussed. In addition, a selection of the rendering results are presented, and our further activities in the field of atmospheric rendering are discussed.
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    A Framework for Interacting with Paper
    (Blackwell Publishers Ltd and the Eurographics Association, 1997) Robinson, Peter; Sheppard, Dan; Watts, Richard; Harding, Robert; Lay, Steve
    This paper reports on ways of using digitised video from television cameras in user interfaces for computer systems. The DigitalDesk is built around an ordinary physical desk and can be used as such, but it has extra capabilities. A video camera mounted above the desk, pointing down at the work surface, is used to detect where the user is pointing and to read documents that are placed on the desk. A computer-driven projector is also mounted above the desk, allowing the system to project electronic objects onto the work surface and onto real paper documents. The animated paper documents project is considering particular applications of the technology in electronic publishing. The goal is to combine electronic and printed documents to give a richer presentation than that afforded by either separate medium.This paper describes the framework that has been developed to assist with the preparation and presentation of these mixed-media documents. The central component is a registry that associates physical locations on pieces of paper with actions. This is surrounded by a number of adaptors that assist with the creation of new documents either from scratch or by translating from conventional hypermedia, and also allow the documents to be edited. Finally the DigitalDesk itself identifies pieces of paper and animates them with the actions described in the registry.
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    EG Network Service
    (Blackwell Publishers Ltd and the Eurographics Association, 1997)
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    Interactive Visualization of Implicit Surfaces with Singularities
    (Blackwell Publishers Ltd and the Eurographics Association, 1997) Rosch, Angela; Ruhl, Matthias; Saupe, Dietmar
    This paper presents work on two methods for interactive visualization of implicit surfaces: physically-based sampling using particle systems and polygonization followed by physically-based mesh improvement which explicitly makes use of the surface-defining equation. While most previous work applied to bounded manifolds without singularities and without boundary (topological spheres) we broaden the scope of the methods to include surfaces with such features, in particular cusp points and surface self-intersections. These aspects are not (yet) essential for computer graphics modelling with implicit surfaces but they naturally occur in simulations of interest in mathematical visualization. In this paper we use the Kummer family of algebraic surfaces as an example.
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    Join Now!
    (Blackwell Publishers Ltd and the Eurographics Association, 1997)
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    Calendar of Events
    (Blackwell Publishers Ltd and the Eurographics Association, 1997)
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    Fifteenth Annual Conference Eurographics UK â 97: University of East Anglia, Norwich, March 24-26, 1997
    (Blackwell Publishers Ltd and the Eurographics Association, 1997)
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    5th EG Workshop on DSV-IS: call for participation
    (Blackwell Publishers Ltd and the Eurographics Association, 1997)
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    Join Now!
    (Blackwell Publishers Ltd and the Eurographics Association, 1997)
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    General Assembly minutes
    (Blackwell Publishers Ltd and the Eurographics Association, 1997)
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    Finally Everyone Can Work With Highly Complex 3D Models
    (Blackwell Publishers Ltd and the Eurographics Association, 1997) Rossignac, Jarek
    In the past, access to 3D databases was restricted to few specialists having the appropriate CAD skills, software, and graphics hardware.The availability of inexpensive graphics support on personal computers, the Internetâ s impact on private and commercial communication, and the emergence of multimedia standards provide the basis for linking CAD databases with other personal productivity and communication tools and for making them accessible to everyone at home, in schools, in hospitals, or in the industry. For example, employees that have no design expertise, customers, and suppliers would benefit from having an easy access to the 3D databases of a company for: collaborative design review, 3D-based multi-media problem reports, collaborative problem solving and tracking, online training and documentation, internet-based part purchasing and subcontracting, demonstration to customers, or advertising. This presentation will address three of the key issues that have so far limited the non-specialistâ s access to 3D databases.First-time or occasional non-expert users need to become instant experts in 3D navigation through Virtual Environments or in the interactive manipulation of digital 3D models, so that they may immediately focus on their tasks, and not waste precious time learning and fighting an unnatural user interface. Immersive VR is not the panacea - other more effective techniques show promise.The data complexity found in commercial CAD databases, especially in the automotive, aerospace, and construction industries, significantly exceeds the capabilities of any interactive graphics system. This situation is not likely to change, since the growth of the complexity and availability of 3D models outpaces the performance improvement of personal computers. Research on the automatic simplification of 3D models and on the use of levels of detail to accelerate the rendering of distant portions of the scene is growing rapidly.The still limited bandwidth of internet communication channels prohibits a pervasive access to large amounts of 3D data. Recent 3D compression techniques reduce the storage requirements for polyhedral 3D models by two orders of magnitudes.
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    Eurographics 1998 Cover Competition
    (Blackwell Publishers Ltd and the Eurographics Association, 1997)
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    Trends and Developments in Computational Geometry
    (Blackwell Publishers Ltd and the Eurographics Association, 1997) De Berg, Mark
    This paper discusses some trends and achievements in computational geometry during the past five years, with emphasis on problems related to computer graphics. Furthermore, a direction of research in computational geometry is discussed that could help in bringing the fields of computational geometry and computer graphics closer together.
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    Fast Analytic Shading and Shadowing for Area Light Sources
    (Blackwell Publishers Ltd and the Eurographics Association, 1997) Tanaka, Toshimitsu; Takahashi, Tokiichiro
    This paper describes a fast analytic algorithm that generates exact highlights and soft shadows from area light sources. In order to realize fast shadowing, we propose the ray-oriented buffer which segments 3D space by following light rays from polygonal sources. Each cell of the buffer stores objects that intersect a related subspace. Candidate objects which may cast shadows onto a point are selected by referring to the buffer. The candidates are then tested with their shadow bounding volumes to suppress objects that never occlude light sources.In addition, we propose the cross scanline clipping algorithm. It quickly determines the exact regions of uncovered area light sources with simple silhouette generation. Both diffuse and specular reflections are computed by integrating light rays from the uncovered sources. Experimental results confirm the high performance of the proposed method.
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    Painting-like Image Emphasis based on Human Vision Systems
    (Blackwell Publishers Ltd and the Eurographics Association, 1997) Tanaka, Toshimitsu; Ohnishi, Noboru
    Regional image emphasis is often evident in paintings and illustrations. This technique increases local contrast while reducing global contrast by amplifying image intensity on shadowed surfaces, reducing intensity on illuminated surfaces, and then expanding contrast at intensity edges. The effects are assumed to result from the visual processing needed to interpolate the real world onto canvas. Therefore, we propose an intensity emphasis method based on human vision. This method simulates the adaptation of photoreceptor cells and the lateral inhibition of receptive fields. These attributes of a vision system are realized by computation of relative intensity and differential intensity in small areas.The proposed method can successfully generate painting-like artifacts, which greatly improves the perception of visual elements displayed in an image. Since the method efficiently reduces the dynamic range of images, it can be used for displaying highlighted images on standard graphic monitors. Experiments on a computer-generated image and a photograph confirm the advantages of our method.
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    Impressions of SIGGRAPH '97: Los Angeles, August 3rd-8th 1997
    (Blackwell Publishers Ltd and the Eurographics Association, 1997)
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    Calendar of Events
    (Blackwell Publishers Ltd and the Eurographics Association, 1997) Greiner, Gunther
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    A Muscle-based Feed-forward Controller of the Human Body
    (Blackwell Publishers Ltd and the Eurographics Association, 1997) Komura, Taku; Shinagawa, Yoshihisa; Kunii, Tosiyasu L.
    There is an increasing demand for human body motion data. Motion capture and physical animation have been used to generate such data. It is, however, apparent that such methods cannot automatically generate arbitrary human body motions. A human body is a redundant multi-linked body controlled by a number of muscles. For this reason, the muscles must work appropriately and cooperatively for controlling the whole body. It is well-known that the human body control system is composed of two parts: The open-loop feed-forward control system and the closed-loop feedback control system. Many researchers have investigated the characteristics of the latter by analyzing the response of a human body to various external perturbations. However, for the former, very few studies have been done. This paper proposes an open-loop feed-forward model of the lower extremities which includes postural control for accurate animation of a human body. Assumptions are made here that the feed-forward controller minimizes a certain objective value while keeping the balance of the body stable. The actual human motion data obtained using a motion capturing technique is compared with the trajectory calculated using our method for verification. The best criteria which is based on muscle dynamics is proposed. Using our method, dynamically correct human animation can be created by merely specifying a few key postures.