Volume 13 (1994)
Permanent URI for this community
Browse
Browsing Volume 13 (1994) by Issue Date
Now showing 1 - 20 of 69
Results Per Page
Sort Options
Item Recovering a Smooth Boundary Representation from an Edge Quadtree and from a Face Octree(Blackwell Science Ltd and the Eurographics Association, 1994) Pla-Garcia, N.The Face Octrees are a representation scheme which is very suitable to represent both smooth free form surfaces and solids with smooth boundary, as well as, to perform operations among them. However, the Face Octree representation is non continuous, thus an algorithm to convert this model to a boundary representation can be necessary. The conversion algorithm makes the advantages of this scheme really significant. The current paper is involved in the conversion from the Face Octrees model to a smooth boundary representation. However, first the planar case is treated.Item Raycasting of Nonregularly Structured Volume Data(Blackwell Science Ltd and the Eurographics Association, 1994) Fruhauf, ThomasRaycasting is an efficient, but computation-intensive technique for the direct rendering of volumetric data. Nonregularly structured volume data is produced in a variety of applications, such as numerical simulation, ultrasonic inspection, or seismic measurement. Unfortunately, in raycasting nonregulary structured grids, sampling data along the rays is even more computation-intensive. One idea might be to resample the data onto a regular grid for further processing. It is shown, that resampling typical grids results either in extreme sub- sampling of the most interesting areas or in data sets too huge to handle. Additionally, no better hardware will overcome the fact that all topology and context information is lost through resampling. Therefore, dedicated algorithms for the raycasting of nonregularly structured volumes are required.We present a new approach for this task, which is based on sending rays through the computational space of a nonregular grid, instead of conventionally raycasting the physical space. This technique overcomes the difficulties in sampling data along the rays, since the computational space is regular by definition. The paper outlines the mathematical operations of this technique as well as its embedding in a rendering algorithm. We have implemented the new raycasting strategy as a module of our interactive visualization system, providing the users with an additional tool for the efficient exploration of their data.Item Beyond WYSIWYG: Display of Hidden Information in Graphics Editors(Blackwell Science Ltd and the Eurographics Association, 1994) Schleich, R.; Durst, M.J.Graphics editors such as computer aided design systems are complex and difficult to use. We attribute this to the fact that only a small part of the information is visible and therefore accessible and understandable. Only the graphics objects themselves are visible, but the relations between these objects remain hidden. We propose an effective way to visualise this information in the form of trees and graphs in so-called structure browsers. A prototype implements this proposal based on an object-oriented application framework for graphics editors.Item Sketching 3D models with 2D interaction devices(Blackwell Science Ltd and the Eurographics Association, 1994) Branco, Vasco; Costa, Antonio; Ferreira, F. NunesThe creation of a 3D shape using CAD tools, namely solid modelers, is difficult and time-consuming. Therefore, these systems are kept away from the conceptual phases of design, perhaps the most important in any product life cycle.The sketch is considered by many people as one of the fundamental techniques during a design s conceptual stages, as it enables high level design options to be explored at low cost. In general, this technique IS under-appreciated in the computer graphics world.In this paper, we present a system called IDeS that tries to combine simplicity and intuition while drawing, with the useful features of the solid modelers, for example, CSG operators.Item Improved Visualisation of Marine Data: Algae and Acid Rain(Blackwell Science Ltd and the Eurographics Association, 1994) Day, A.M.; Turner, S.M.; Arnold, D.B.Item A Theoretical Framework for Physically Based Rendering(Blackwell Science Ltd and the Eurographics Association, 1994) Lafortune, Eric P.; Willems, Yves D.In this paper we introduce the concept of the global reflection distribution function which allows concise formulation of the global illumination problem. Unlike previous formulations it is not geared towards any specific algorithm. As an example of its versatility we derive a Monte Carlo rendering algorithm that seamlessly integrates the ideas of shooting and gathering power to create photorealistic images.Item Reducing The Latency In Head-Mounted Displays By A Novel Prediction Method Using Grey System Theory(Blackwell Science Ltd and the Eurographics Association, 1994) Wu, Jiann-Rong; Ouhyoung, MingIn this paper we propose a novel prediction method for the head motion using Grey System theory, where a 6D tracker is attached to an HMD on a user s head in virtual reality applications. Our prediction method using Grey System Model can greatly reduce the latency by at least one half and reduce image jittering. A system latency below 100 ms or even 50 ins can be achieved, even though without prediction the latency is around 200 ms. Using 6 points in prediction with Grey System Model is currently the best in tracker prediction as we tried from 2 points to 10 points.In order to measure the latency, we also propose a way to measure it in an HMD system precisely and conveniently. During the process, we have implemented four different prototypes respectively on a PC486, a SUN SparcStation10, an SGI IndigoR4000, and a high performance computer image generator. The computation complexity of our prediction method is relatively low and therefore real time requirement is easily met.Item Spectral Data Modeling for a Lighting Application(Blackwell Science Ltd and the Eurographics Association, 1994) Deville, Pascal M.; Merzouk, Slimane; Cazier, Dorothee; Paul, Jean C.In computer graphics, image generation uses the RGB colorimetric system. However, this system does not produce an accurate simulation of the spectral characteristics of both light and material, due to the fact that it is device dependent. Indeed, to get realistic images, the image calculation process must deal with spectral characteristics of lights and materials and with the problem of sampling the wavelength domain. Methods have been shown that are a good way to solve the two problems mentioned above, however, these approaches do not take into account complex spectrums (discontinuous). In this paper, we propose a method which removes the constraints imposed by the current methods. Our method is based upon an algorithm of spectrum analysis.Item 3D Visualization for 2D GIS: an Analysis of the Users Needs and a Review of Techniques*(Blackwell Science Ltd and the Eurographics Association, 1994) Giertsen, Christopher; Lucas, AnneMost of the existing geographical information systems (GIS) make limited use of algorithms for advanced computer graphics and visualization. One explanation is that few attempts are made to identify the visualization needs for different uses of GIS, and to couple such needs to the available algorithms. Another explanation is that most GIS are designed to handle two-dimensional (20) data with few obvious relationships to three-dimensional (30) visualization.In an attempt to provide a better understanding of the application of visualization in GIS, we propose a conceptual framework linking several aspects of the two fields. At the user-level, we link different uses of GIS to different categories of audience and presentation styles. At the level of implementation, we first propose different ways to create 3D data for visualization from 2D GIS data, and then we review algorithms and techniques for 3D visualization with respect to support of different presentation styles.Item Computer Generated Copper Plates(Blackwell Science Ltd and the Eurographics Association, 1994) Leister, WolfgangMaking computer generated copper plates with image generation algorithms is presented. The method uses a kind of volume texturing in connection with image processing algorithms, and is suitable for implementation in a ray tracing algorithm. Experience shows that this method is especially interesting for illustrations in books and for generating icons on user interfaces.Item A Formal Approach to the Specification of Graphic Object Functions(Blackwell Science Ltd and the Eurographics Association, 1994) Torres, J.C.; Clares, B.Graphic objects are an abstract mathematical model for graphic systems. The model is an algebraic approach to represent graphic information, which include modelling operations. This formalism require some method to describe normal graphic procedures, such as changing the object colour or texture mapping, as these procedures are essential to represent graphic processes.This paper extends the theory by introducing the concept of graphic object functions. A graphic object function transforms one graphic object into another, changing its visual appearance or its geometric properties. A formal definition of graphic functions is given, with a characterization of two special kinds of graphic object functions: filters and object transference functions. These two kinds of functions can be used to perform normal graphic operations, such as changing colours, texture mapping or clipping.Equivalence relationships between graphic objects induced by functions are also studied. These relationships establish an hierarchical structure on the graphic object set.Item Solid Modeling Based on a New Paradigm(Blackwell Science Ltd and the Eurographics Association, 1994) Yoshida, Norimasa; Shiokawa, Masato; Yamaguchi, FujioThe technique of solid modeling is essential in CAD/CAM applications, and is currently well established. However, problems remain, such as the lack of uniformity in geometric computations and the lack of stability of Boolean operations of two solids. In this paper, we introduce a theoretical solid modeling system that operates on boundary representations of polyhedral objects and is based on a new paradigm. The characteristics of the system are the following: (I) in Boolean Operations and modeling transformations, all geometric computations are performed by the 4 ? 4 determinant method or the 4 ? 4 matrix method in homogeneous space, which allows the system to avoid division operations, (2) all geometric computations are performed by the exact integer arithmetic, which makes the geometric algorithms stable and simple, and (3) primitive solids are constructed consistently in the integer domain, and the consistency is assured throughout Boolean operations and transformations.Item Animation using NURBS(Blackwell Science Ltd and the Eurographics Association, 1994) Preston, M.; Hewitt, W. T.All animation, whether generated by pen or processor, is concerned with the changing behaviour of synthetic actors through time. Computer animation has allowed an animator to regard different actors as functionally equivalent entities for the purpose of generating their behaviours. This has opened the door to visually impressive effects, such as actors changing their appearance, thereby becoming other actors.For NURBS to become a tool which is useful to the writer of animation packages, it is necessary to provide this ability to in-between objects of different appearances through time.This paper aims to present a technique for creating higher dimensional NURBS to model object deformation, as well as to illustrate its advantages.Item How to Render Frames and Influence People(Blackwell Science Ltd and the Eurographics Association, 1994) Strothotte, Thomas; Preim, Bernhard; Raab, Andreas; Schumann, Jutta; Forsey, David R.Rendering systems generally treat the production of images as an objective process governed by the laws of physics. However, perception and understanding on the part of viewers are subjective processes influenced by a variety offactors. For example, in the presentation of architectural drawings, the apparent precision with which the drawings are made will affect whether the viewer considers the design as part of a preliminary design or as part of a final polished project, and to some extent the level of confidence the viewer has in the encoded information.In this paper we develop techniques for rendering images in a way that differs from the usual photorealistic or wire-frame output of renderers. In particular, our techniques allow a user to adjust the rendering of a scene to produce images using primitives with variable degrees of precision, from approximations that resemble vague"five-minute-sketches" to more mature but still hand-drawn images. We provide a theoretical framework for analysing the information flow from the computer to the user via such images. Finally, we describe the design and implementation of a prototypical renderer and show examples of its output.Item Selective Visualization of Vector Fields(Blackwell Science Ltd and the Eurographics Association, 1994) van Walsum, Theo; Post, Frits H.In this paper, we present an approach to selective vector field visualization. This selective visualization approach consists of three stages: selectdon creation, selection processing and selective visualization mapping. It is described how selected regions, called selections, can be represented and created, how selections can be processed and how they can be used in the visualization mapping. Combination of these techniques with a standard visualization pipeline improves the visualization process and offers new facilities for visualization. Examples of selective visualization of fluid flow datasets are provided.Item PREMO - An Initial Approach to a Formal Definition(Blackwell Science Ltd and the Eurographics Association, 1994) DUCE, D.A.; DUKE, D.J.; ten HAGEN, P.J.W.; REYNOLDS, G.J.Many descriptions of multimedia programming systems are starting to appear in the literature, but little work has yet been done on how to formally specify and reason about such systems. This paper is a contribution on the use of formal description techniques for the specification of multimedia systems and explores a style in which the Object-Z notation from the University of Queensland can be used to specify some of the properties and functionality of such systems. The work has been carried out with reference to the role of formal description techniques in the presentation of ISO/IEC International Standards and in particular to the Premo project in ISO/IEC JTCl/SC24.Item The Mesh Propagation Algorithm for Isosurface Construction(Blackwell Science Ltd and the Eurographics Association, 1994) Howic, C.T.; Blake, E.H.A new algorithm, Mesh Propagation, is presented for the generation of isosurfaces from three-dimensional discrete data sets. While producing the same surface mesh as that generated by a corrected Marching Cubes algorithm, its characteristic is that it constructs an isosurface using connected strips of dynamically triangulated polygons. This compact data structure speeds up surface construction and reduces surface storage requirements. The surface can also be displayed more quickly, particularly where there is hardware support for rendering triangle strips.With engineering as well as medical imaging applications in mind, the algorithm can be used with both irregular and rectilinear grids of data, the primitive volume elements need not be hexahedral only, and volumes of heterogeneous polyhedral elements are supported without traversal complications.The algorithm propagates through the cells in the grid and uses the same lookup table topologies as Marching Cubes to determine patches of surface-element intersection- additional tables are used for non-hexahedral elements. The surface patches are dynamically coded into triangle strips which are then concatenated and linked to construct the surface. The data structures used for propagating through the volume overcome the topological ambiguities associated with table-based methods of surface construction and no holes are generated in the final mesh.Item Ray Traversal of Spatial Structures(Blackwell Science Ltd and the Eurographics Association, 1994) Kuzmin, Yevgeniy P.This article presents an efficient algorithm for ray traversal of uniform and hierarchical spatial structures. Only simple integer and logical operations are used. The problem of error accumulation during ray casting is considered. The algorithm is well suited for efficient software and hardware implementation.Item A Schematic Entry Drawing Capability in a Linearised Hypermedia System(Blackwell Science Ltd and the Eurographics Association, 1994) Benest, I. D.This paper describes a linearised hypermedia system, called the Book Emulator, that generally supports the capture of diagrammatic specifications such as SSADM and electronic circuit diagrams, and the capture of mathematical notations such as Z. Since the Book Emulator can be closely coupled to applications, it can be used as the user-interface to that application. Doing so automatically provides a conferencing mechanism on behalf of applications and a mechanism for recording the engineering analyses performed by the application. It is argued that this is the next and higher step in the trend to separate the user-interface from the application. The schematic entry mechanism has been designed to minimise the user s physical and mental effort so that the user may concentrate on drawing strategy. This is achieved by minimising the number of selections (steps) required to reach an atomic goal, and by refraining from hiding functionality in menus. The paper concludes with an indication of how the generalised schematic capture mechanism might be exploited in systems that allow end- users to organise and specify their information requirements.Item A Semantics-based Approach for the Design and Implementation of Interaction Objects(Blackwell Science Ltd and the Eurographics Association, 1994) Paterno , F.; Leonardi, A.Although tools for developing graphical user interfaces are becoming increasingly popular, they do not usually highlight precisely which key elements developers should take into account. This still entails considerable expertise in developing user interfaces. In this paper we present an approach to overcome these problems. Our approach is based on a model for interaction objects and a corresponding design space. This is supported by a toolkit where the available interaction objects are initially classified by their semantics whereas in most current toolkits they are investigated by their appearance. This facilitates designers and developers in identifying the interactors needed in order to obtain an Interactive System supporting user tasks.