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Item The ARGOSI Classification Scheme for Graphics and Networking Applications(Blackwell Science Ltd and the Eurographics Association, 1993) Sutcliffe, D.C.; Gallop, J.R.; Maybury, R.; Day, R.A.; Duce?, D.A.; Reynolds?, G.J.ARGOSI is a project concerned with the relationship between standards for graphics and networking, as rejected in its full title: Applications Related Graphics and OSI Standards Integration. It is a collaborative project between eleven European organizations and is funded under the Esprit-Il programme of the Commission of the European Community.In order to achieve integration of graphics and OSI standards and to meet the requirements of applications, it is necessary to understand the needs of applications to transfer graphical information and the networking services required to support this. A major part of the ARGOSI project has been to derive a classification framework for applications based on a set of metrics describing their use of graphics and networking. Once classified, a study is to be made to determine the set of graphics and OSI standards that will satisfy the requirements of each group of applications or to identify deficiencies or omissions in the set of current standards that prevent the requirements being met. The classification scheme is believed to be a major stepforward in the field.Item A Rendering Algorithm for Discrete Volume Density Objects(Blackwell Science Ltd and the Eurographics Association, 1993) Blasi, Philippe; Le Saec, Bertrand; Schlick, ChristopheWe present a new algorithm for simulating the effect of light travelling through volume objects. Such objects (haze, fog, clouds.) are usually modelized by voxel grids which define their density distribution in a discrete tridimensional space. The method we propose is a two-pass Monte-Carlo ray-tracing algorithm that does not make any restrictive assumptions neither about the characteristics of the objects (both arbitrary density distributions and phase functions are allowed) nor about the physical phenomena included in the rendering process (multiple scattering is accounted for). The driving idea of the algorithm is to use the phase function for Monte-Carlo sampling, in order to modify the direction of the ray during scattering.Item Using Multimedia to Support Cooperative Editing(Blackwell Science Ltd and the Eurographics Association, 1993) Santos, A.; Tritsch, B.By Cooperative Editing we mean the coordinated manipulation of information by a group of authors. During the editing process the (co-)authors need to communicate their ideas, drafts and constraints (remotely or face-to-face) until a final version of the information is achieved. For the different phases of this process - discussion of ideas, editing, cross-checking - different media or media integration are adequate. Furthermore, analysing the transition from individual work to group work, within different human activities, two pitfalls are often detected if computer support is considered: a) technological communication difficulties, especially if the group is remotely located on heterogeneous hardware, associated with a fall in productivity and frequent social inadequacies of the group s computer support- b) the lack of integrated media processing tools available for group editing.In order to solve these problems, we suggest that Multimedia can be applied in two ways: to effectively support the necessary group communication links- and to enhance the expressiveness of the information edited. To test this statement we have been conceptualising and implementing a prototype system. Most of the techniques involved can be used in other tools that need multimedia capabilities or that support other specific types of group activities.The innovative aspects of the work are the use of multimedia techniques to support demanding applications, possibly on cross-platforms, and the integration of several concepts to support cooperation.Item A Fractal Method for Digital Elevation Model Construction and its Application to a Mountain Region(Blackwell Science Ltd and the Eurographics Association, 1993) Brivio, Pietro Alessandro; Marini, DanieleThis paper presents and discusses the results of a methodology for the construction of Digital Elevation Models (DEM), based on mathematical principles of fractal geometry. Classical approaches to DEM are founded on numerical methods of interpolation or approximation of data extracted from contour lines of standard topographic maps. Fractal geometry opens a new and innovative approach in which the irregularity, erraticity and self similarity of fractal structures mimics at best the typical behaviour of high mountain profiles. The adoption of fractal methods requires the identification of the fractal dimension D for a given data set. The determination of the fractal dimension D can be achieved applying some special mathematical method on finite set of samples. Different methods. for D estimation are presented. Once the fractal dimension is given, it is possible to reconstruct a surface relief using different fractal methods which interpolate the original set of elevation data. Our research has also investigated two different interpolation methods, fBm and IFS, both confirming that the fractal approach is very well suited for high relief terrain modeling. Photo realistic rendering of the computed DEM allows to appreciate the quality of the reconstruction through visual inspection.Item Ray Tracing an Octree: Numerical Evaluation of the First Intersection(Blackwell Science Ltd and the Eurographics Association, 1993) Gargantini, I.; Atkinson, H. H.Item DIGIS A Graphical User Interface Design Environment for Non-Programmers(Blackwell Science Ltd and the Eurographics Association, 1993) de Bruin, Hans; Bouwman, Peter; van den Bos, JanDIGIS (Direct Interactive Generation of Interactive Systems) is a graphical UI design environment for non-programmers that facilitates the design of all aspects of a UI with direct manipulation techniques. DIGIS is based on four models: an object model, a system task model, an interaction model and a dialogue control model. These four models describe an interactive system at a high conceptual level which allows a UI designer to quickly construct a high quality direct manipulation UI that supports undo-redo, context-sensitive help and guidance, and connect the UI with the (existing) application.Item Scale-Invariant Minimum-Cost Curves: Fair and Robust Design Implements(Blackwell Science Ltd and the Eurographics Association, 1993) Moreton, Henry P.; Sequin, Carlo H.Four functionals for the computation of minimum cost curves are compared. Minimization of these functionals result in the widely studied Minimum Energy Curve (MEC), the recently introduced Minimum Variation Curve (MVC), and their scale-invariant counterparts, (SI-MEC, SI-MVC). We compare the stability and fairness of these curves using a variety of simple interpolation problems. Previously, we have shown MVC to possess superior fairness. In this paper we show that while MVC have fairness and stability superior to MEC they are still not stable in all configurations. We introduce the SI-MVC as a stable alternative to the MVC. Like the MVC, circular and helical arcs are optimal shapes for the SI-MVC.Additionally, the application of scale invariance to functional design allows us to investigate locally optimal curves whose shapes are dictated solely by their topology, free of any external interpolation or arc length constraints.Item Cooperative Visualization of Computational Fluid Dynamics(Blackwell Science Ltd and the Eurographics Association, 1993) Gerald-Yamasaki, Michael J.Tempus Fugit/Interview is a computational fluid dynamics visualization application for which processing is distributed between high performance graphics workstations and supercomputers. Facilities are provided in the application for more than one user to view shared images creating a cooperative visualization environment. The way in which the computation is partitioned between the super computer and the workstations is critical to the capability of the application to present simultaneous, identical, animated images of fluid dynamics to more than one user.Item Symmetrical Patterns from Dynamics(Blackwell Science Ltd and the Eurographics Association, 1993) Chung, K. W.; Chan, H. S. Y.Automatic generation of symmetrical patterns belonging to all seventeen wallpaper groups is considered from a dynamical system s point of view. A pseudo-code of the algorithm is provided to generate the computer graphics. The method is shown to be able to create unlimited varieties of patterns and demonstrates the possibility of relaxing the crystallographic restriction to produce aperiodic patterns.Item Modeling of Skylight and Rendering of Outdoor Scenes(Blackwell Science Ltd and the Eurographics Association, 1993) Tadamura, Katsumi; Nakamae, Eihachiro; Kaneda, Kazufumi; Baba, Masashi; Yamashita, Hideo and Nishita, TomoyukiPhotorealistic animated images are extremely effective for pre-evaluating visual impact of city renewal and construction of tall buildings. In order to generate a photorealistic image not only the direct sunlight but also skylight must be considered.This paper proposes a method of high-fidelity image generation for photorealistic outdoor scenes based on the following ideas: * 1The intensity distribution of skylight taking account of scattering and absorption due to particles in the atmosphere which coincides with CIE standard skylight luminance functions is sought, and realistic images considering about spectrum distribution of skylight for any altitude of the sun can be easily and accurately displayed. * 2A rectangular parallelepiped with a specialized distribution of intensity simulating the skylight is introduced for efficient calculation of illumination due to skylight, and by employing a graphics hardware calculation of the skylight illuminance taking into account shadow effects is obtained with high efficiency- these techniques can be used to generate sequences of images, making animations possible at far lower calculation cost than previous methods.