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# Volume 12 (1993)

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Item 3D Computational Morphology(Blackwell Science Ltd and the Eurographics Association, 1993) Veltkamp, Remco C.Show more Computational Morphology is the analysis of form by computational means. This discipline typically uses techniques from Computational Geometry and Computer Aided Geometric Design. The present paper is more specifically about the construction and manipulation of closed object boundaries through a set of scattered points in 3D. Original results are developed in three stages of computational morphology: * impose a geometrical structure on the set of points- * construct a polyhedral boundary surface from this geometrical structure- * build a hierarchy of polyhedral approximations together with localization information-The economic advantage of this approach is that there is no dependency on any specific data source. It can be used for various types of data sources or when the source is unknown.Show more Item A 4D Ray Tracing(Blackwell Science Ltd and the Eurographics Association, 1993) Maurel, Herve; Duthen, Yves; Caubet, ReneShow more We are going to present a survey of techniques using temporal coherence in between frames to render animation sequences with ray tracing. A new method using temporal coherence in the ray space (lightpath of rays) is proposed. The goal of this technique is to factorize intersection and illumination calculations over the frames of the sequence. An optical event springing out many times in the sequence is computed once. The method is based upon 4D intersection calculations between temporal rays and moving objects. At the end of this paper, we present measurements showing the number of rays we need not calculate with our solution. These results come from simulating the algorithm behavior through a graphic and statistic ray analyser tool.Show more Item Abstract Interaction Objects(Blackwell Science Ltd and the Eurographics Association, 1993) Duke, D.J.; Harrison, M.D.Show more The concept of an interactor has been introduced by Faconti and Paterno [6] as an abstraction of an entity in interactive graphics capable of both input and output. However the notion of interaction object need not be confined to graphics systems- it represents a useful structure for thinking and reasoning about the behaviour of interactive systems in general. As part of Esprit Basic Research Action 7040 (Amodeus-2) we are using the concept of interactor, and existing work on state-based processes and agents, to develop a model and theory of interactive systems. In this paper we describe two formal models for interaction objects and sketch how they can be used to build a small vocabulary of operators to support the rigorous specification of a graphics system. Our model differs from the approach of Faconti and Paterno in that it abstracts away from any specific graphics framework and is thus suited to the level of abstraction demanded by formal approaches to system development.Show more Item Accurate and Consistent Reconstruction of Illumination Functions Using Structured Sampling(Blackwell Science Ltd and the Eurographics Association, 1993) Drettakis, George; Fiume, EugeneShow more The study of common classes of diffuse emitters, such as planar convex polygons, reveals several interesting properties of the functions of illumination these emitters cast on receiver surfaces. Some properties, such as the position of the maximum and the curvature are of particular interest for sampling and reconstruction of illumination across receivers. A computationally efficient approach is presented that identifies these properties, and uses them to select samples of illurnination. In addition these properties are used to determine upper bounds on the error due to linear and quadratic interpolants. These bounds are then used to adaptively subdivide the non-uniform sampling grid, resulting in accurate reconstruction. Results show that the method reduces the error compared to uniform approaches, and produces more consistent animated sequences.Show more Item ANIMA: An Interactive Tool for Scientific Data Animation(Blackwell Science Ltd and the Eurographics Association, 1993) Moltedo, Laura; Morigi, SerenaShow more This paper describes an animation interactive system that produces image sequences used to study the numerical results of scientific simulations. The fundamental goal of the system is to provide an easy method for observing and exploring scientific computation during its space-time evolution. To do that it is necessary to combine simulation processes, algorithmic and key frame animation with geometric transformations, light effects and camera movements. ANIMA allows the researcher to use animation without special programming, with the aid of a graphic user interface. Modelling, rendering, motion control and synchronization of graphic objects are interactively specified by the animator in order to define an animation script. The system development methodology follows an object-oriented technique using modular programming, abstract data type definition, and graphic metaphor with user interface menus.Show more 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.Show more 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.Show more Item Automatic Reconstruction of Buildings from Stereoscopic Image Sequences(Blackwell Science Ltd and the Eurographics Association, 1993) Koch, ReinhardShow more A vision-based 3-D scene analysis system is described that is capable to model complex real-world scenes like streets and buildings automatically from stereoscopic image pairs. Input to the system is a sequence of stereoscopic images taken with two standard CCD Cameras and TV lenses. The relative orientation of both cameras to each other is known by calibration. The camerapair is then moved throughout the scene and a long sequence of closely spaced views is recorded. Each of the stereoscopic image pairs is rectified and a dense map of 3-D suface points is obtained by area correlation, object segmentation, interpolation, and triangulation. 3-D camera motion relative to the scene coordinate system is tracked directly from the image sequence which allows to fuse 3-D surface measurements from different viewpoints into a consistent 3-D model scene. The surface geometry of each scene object is approximated by a triangular surface mesh which stores the suface texture in a texture map. From the textured 3-D models, realistic looking image sequences from arbitrary view points can be synthesized using computer graphics.Show more Item Boolean Operations and Spatial Complexity of Face Octrees.(Blackwell Science Ltd and the Eurographics Association, 1993) Pla-Garcia, NuriaShow more Most of the existing representation schemes of free form surfaces or objects with free form boundary are not capable to compute efficiently boolean operations and other usual geometric interrogations. Classical octrees, proposed to overcome this drawback, require large amounts of memory. Face Octrees was a proposal suitable in the case of smooth surfaces or objects with smooth boundary. In this paper, different aspects of this model are discussed. In fact, it is focussed on the description of boolean operation algorithms using this model, proving that it solves the first problems, and on the computation of spatial complexity bounds. These bounds allow an evaluation of the fitness of each of the existing octree models in a given situation, showing the advantage of Face Octrees when the boundaries are smooth (curvatures are small).Show more Item The Cone of Normals Technique for Fast Processing of Curved Patches(Blackwell Science Ltd and the Eurographics Association, 1993) Shirmun, Leon A.; Abi-Ezzi, Salim S.Show more The cone of normals technique for curved surface patches allows to perform various quick tests at the patch level such as front- or backfacing test, light influence test, and existence of silhouette edges test. For a given patch, a truncated cone of normals is constructed at creation time, which contains all points and all normal directions of the patch. At traversal time, a simple scalar product test determines whether the whole patch is backfacing or frontfacing, so that the costly step of tessellating the patch is avoided in case of patch level face culling. In addition, the technique quickly determines which light sources have no influence on a patch, and which patches have no silhouette edges. The technique can also be used for other surface primitives, such as triangular strips and quadrilateral meshes,Show more Item Cooperative Visualization of Computational Fluid Dynamics(Blackwell Science Ltd and the Eurographics Association, 1993) Gerald-Yamasaki, Michael J.Show more 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.Show more Item DaScript3D Integrating 3D Graphics in a Page Description Language(Blackwell Science Ltd and the Eurographics Association, 1993) Samara, VeronikaShow more Despite the necessity of producing high-quality documents comprising all aspects of electronic publishing, there is still no system available that can generate and integrate two-dimensional (2D) graphics, three-dimensional (3D) graphics and high-quality text electronically. This situation becomes especially critical in the area of technical documentation where graphics as well as text play a major role. DaScript3D introduces 3D extensions able to handle and integrate 2D and 3D graphics as well as text in one tool. Based on the page description language PostScript, DaScript3D offers the power of PostScript on the one hand, and, on the other hand, all the characteristics and advantages of a 3D system.Show more Item A Declarative Design Method for 3D Scene Sketch Modeling(Blackwell Science Ltd and the Eurographics Association, 1993) Donikian, Stephane; Hegron, GerardShow more In this paper, we present a dynamic model associated with an intelligent CAD system aiming at the modeling of an architectural scene sketch. Our design methodology has been developed to simulate the process of a user who tries to give a description of a scene from a set of mental images. The scene creation is based on a script which describes the environment from the point of view of an observer who moves across the scene. The system is based on a declarative method viewed as a stepwise refinement process. For the scene representation, a qualitative model is used to describe the objects in terms of attributes, functions, methods and components. The links between objects and their components are expressed by a hierarchical structure, and a description of spatial configurations is given by using locative relations. The set of solutions consistent with the description is usually infinite. So, either one scene consistent with this description is calculated and visualized, or reasons of inconsistency are notified to the user. The resolution process consists of two steps: firstly a logical inference checks the consistency of the topological description, and secondly an optimization algorithm deals with the global description and provides a solution. Two examples illustrate our design methodology and the calculation of a scene model.Show more Item The Determination of Form-Factors by Lookup Table(Blackwell Science Ltd and the Eurographics Association, 1993) Sun, Jizhou; Zou, L.Q.; Grimsdale, R.L.Show more Current methods for computer image synthesis using the radiosity algorithm rely heavily on the calculation of geometrical properties, known as form-factors, which quantify the energy exchange between pairs of surfaces in the environment. In this paper, a new method for form-factor calculation is presented, in which form-factors from a differential area to a finite area with various geometric orientations and dimensions can be determined by the summation of three weighted directional form-factors. The three directional form-factors are mutually independent and can be pre-calculated and stored in a lookup table accessed by two indices. Thus, the determination of the generally used complex form-factor integral is greatly simplified and mainly replaced by accessing a pre-established lookup table. Quantitative comparisons of Wallace s ray casting method and the method presented indicate that the new method can provide more accurate form-factors, which implies that the number of sample points necessary on each source patch is comparatively reduced and the process of form-factor calculation can be accelerated.Show more 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, JanShow more DIGIS (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.Show more Item Direct 3D Manipulation Techniques for Interactive Constraint-based Solid Modelling(Blackwell Science Ltd and the Eurographics Association, 1993) Fa, Mingxian; Fernando, Terrence; Dew, Peter M.Show more This paper presents a novel constraint-based 3D manipulation approach to interactive constraint-based solid modelling. This approach employs a constraint recognition process to automatically recognise assembly relationships and geometric constraints between entities from 3D manipulation. A technique referred to as allowable motion is used to achieve accurate 3D positioning of a solid model by automatically constraining its 3D manipulation without menu interaction. A set of virtual design tools, which can be used to construct constraint-based solid models within a virtual environment, are also supported. These tools have been implemented as functional 3D objects associated with several pre-defined modelling functions to simulate physical tools such as a drilling tool and T-square. They can be directly manipulated by the user, and precisely positioned relative to other solid models through the constraint-based 3D manipulation approach. Their modelling functions can be automatically triggered, depending upon their associated constraints and the user s manipulation manner. A prototype system has been implemented to demonstrate the feasibility of these techniques for model construction and assembly operations.Show more Item A Dynamic Gesture Language and Graphical Feedback for Interaction in a 3D User Interface(Blackwell Science Ltd and the Eurographics Association, 1993) Bordegoni, Monica; Hemmje, MatthiasShow more In user interfaces of modern systems, users get the impression of directly interacting with application objects. In 3D based user interfaces, novel input devices, like hand and force input devices, are being introduced. They aim at providing natural ways of interaction. The use of a hand input device allows the recognition of static poses and dynamic gestures performed by a user s hand.This paper describes the use of a hand input device for interacting with a 3D graphical application. A dynamic gesture language, which allows users to teach some hand gestures, is presented. Furthermore, a user interface integrating the recognition of these gestures and providing feedback for them, is introduced. Particular attention has been spent on implementing a tool for easy specification of dynamic gestures, and on strategies for providing graphical feedback to users interactions. To demonstrate that the introduced 3D user interface features, and the way the system presents graphical feedback, are not restricted to a hand input device, a force input device has also been integrated into the user interface.Show more Item Electronic Kaleidoscopes for the Mind(Blackwell Science Ltd and the Eurographics Association, 1993) Pickover, Clifford A.; Rudolph, LarryShow more The goal ofthis article is to present an informal introduction and tutorial on aestheticallypleasing kaleidoscopic images. The article is intended for the non-mathematical reader interested in computer art. Simple generating formulas and recipes are included.Show more Item Extracting contour lines from a hierarchical surface model(Blackwell Science Ltd and the Eurographics Association, 1993) De Floriani, Leila; Mirra, Daniela; Puppo, EnricoShow more The Hierarchical Triangulated Irregular Network (HTIN) is a structure for representing 2?-dimensional surfaces at different levels of detail through piecewise-linear approximations based on triangulations of the surface domain. In this paper, we present two algorithms that allow extracting a representation of the surface and contour lines at a given level of detail, directly from the HTIN.Show more Item Fast Spheres(Blackwell Science Ltd and the Eurographics Association, 1993) Patterson, John W.Show more A new method for generating sphere-like images, using parabolic surfaces delimited by Bresenham s circle- generation algorithm, is presented. In many cases the resultant images are indistinguishable from spheres illuminated from a given single direction. The main form of the algorithm uses first and second integer differences to minimise computation and uses typically not more than one floating-point calculation per sphere. Two variants of the algorithm are given, one optimized for the special case of the light-source being behind the view-point, and one in which values are calculated for a z-buffer hidden-surface algorithm at the same time as the pixel values. The difference formulae can be exploited by differencing hardware or digital signal processors although very little arithmetic, typically five low-weight integer operations, including address calculation operations, is required per pixel on a conventional architecture.Show more Item Form Factor Calculation: a New Expression with Implementations on a Parallel T.Node Computer(Blackwell Science Ltd and the Eurographics Association, 1993) Michelin, Sylvain; Maffeis, Gualtiero; Arques, Didier; Grossetie, Jean ClaudeShow more The radiosity technique uses the heat transfer theory to define a view-independent illumination model. For complex scenes, calculation of this model is very time-intensive, due largely to the determination of a geometric factor, defined with a double area integral, and named form factor. This paper presents a new expression of the form factor, which can be reformulated, in a computationally more efficient manner, as a simple line integral for planar polygonal convex surfaces that are perfectly diffuse.Recently, parallel computers have been used to decrease calculation time. Previous work is focused mainly on distributed implementations of a method, the progressive refinement method, widely used for complex environments. The T.Node is a completely reconfigurable MIMD machine, based on the transputer chip. In this paper, we compare a parallel implementation of the progressive refinement method with a direct method which takes into account the memory capabilities of this kind of machine.Show more