Issue 3

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https://diglib.eg.org/handle/10.2312/56

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Variational Surface Design and Surface Interrogation
(Blackwell Science Ltd and the Eurographics Association, 1993) Hagen, H.; Hahmann, St.; Bonneau, G.-P.
The generation of technical smooth surfaces from a mesh of three-dimensional data points is an important problem in geometric modelling. In this publication we give a survey of some new techniques based on a calculus of variation approach. Apart from the pure construction of these surfaces, the analysis of their quality is equally important in the design and manufacturing process. Generalized focal surfaces are presented here as a new surface interrogation tool.
Photo-Realistic Imaging of Digital Terrains
(Blackwell Science Ltd and the Eurographics Association, 1993) Cohen, Daniel; Shaked, Amit
We present a method for the generation of photo-realistic images of views over terrain datasets by mapping a digital aerial photograph on a perspective projection of a digital elevation map. We use high resolution for both digital maps to increase the quality and the realism of the image at the cost of the overhead of processing very large data bases. In the core of this paper we present an accelerated ray casting technique based on a new algorithm of traversing a pyramidal data structure. Unlike other known traversal techniques, the cost of a single step of the algorithm consists of a few additions, shifts and comparisons only.
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, Jan
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.
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.
A Rendering Algorithm for Discrete Volume Density Objects
(Blackwell Science Ltd and the Eurographics Association, 1993) Blasi, Philippe; Le Saec, Bertrand; Schlick, Christophe
We 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.
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.
A New Paradigm for Geometric Processing
(Blackwell Science Ltd and the Eurographics Association, 1993) Yamaguchi, Fujio; Niizeki, Masatoshi
A new paradigm for geometric processing is proposed. The paradigm can be featured by the four key phrases: (1) Totally Four Dimensional Homogeneous Processing, (2) 4 ? 4 Matrix Method and 4 ? 4 Determinant Method, (3) Integer Arithmetic with Adaptive Data-Length Control Technique, (4) Systematic Paradigm Structures Based on the Duality.
GKS-9x: Some Implementation Considerations
(Blackwell Science Ltd and the Eurographics Association, 1993) Damnjanovic, L.B.; Duce, D.A.; Robinson, S.K.
The Graphical Kernel System (GKS) was published as an ISO standard for computer graphics programming in August 1985. GKS is now undergoing revision in ISO/IEC and at the time of writing the text of the Draft International Standard of GKS-9x was being finalized. This paper presents a way in which a key part of the new functionality in GKS-9x, namely namesets and selection criteria, can be implemented effectively.
Landscapes Synthesis Achieved through Erosion and Deposition Process Simulation
(Blackwell Science Ltd and the Eurographics Association, 1993) Roudier, P.; Peroche, B.; Perrin, M.
This paper describes an original approach to terrain evolution in landscapes synthesis. In order to create some realistic landforms, we simulate geologically contrasted terrains and apply to them deterministic erosion processes. This allows us to relate the erosion on any point of the landsurface to local geological parameters. Any height field may be chosen as an initial topographic surface. Small perturbations may be introduced to avoid unpleasant regularities. A 3D model defines the geological parameters of each point according to its elevation. Our method is iterative: at each step, rock removal and possible alluvial deposition are computed at each point of the landsurface. The available erosion laws simulate mechanical erosion, chemical dissolution and alluvial deposition. At the end of each iteration, a new landsurface and the corresponding river network are created. Landsurfaces can be visualized at the final stage by two rendering algorithms including natural textures mapping. The stream network and the ridges may also be visualized.
Fast Spheres
(Blackwell Science Ltd and the Eurographics Association, 1993) Patterson, John W.
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.
3D Computational Morphology
(Blackwell Science Ltd and the Eurographics Association, 1993) Veltkamp, Remco C.
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.
Storage Support for Multidimensional Discrete Data in Multimedia Databases
(Blackwell Science Ltd and the Eurographics Association, 1993) Furtado, Paula; Teixeira, Jose Carlos
Multidimensional discrete data (MDD) is enormously important for multimedia applications since diverse types of such data are used simultaneously by any multimedia application. However, multidimensional discrete data is not adequately supported by most existing database systems.In this paper we discuss the major management requirements imposed by such data on multimedia database management systems both at the conceptual level and at the internal level. At the internal level, the spatial structure of the data must also be preserved and special emphasis must be given to the efficient spatial access to subrectangles of very large data of arbitrary dimensionality.Our major contribution is the presentation of a Storage Manager for this kind of data which preserves the spatial nature of the data at the internal level of the database management system and provides efficient spatial access. This Storage Manager is based on an innovative combination of the subdivision of data in multidimensional tiles and of a spatial index to access those tiles. Furthermore, it supports advanced registration data.The lower level modules of the Storage Manager are responsible for the access to the data stored in secondary storage. The implementation of these modules can rely on any secondary storage access system to access data on disk. The Storage Manager was implemented using the functionality of a relational database system. The implementation of this relational Storage Manager is presented.
Extracting contour lines from a hierarchical surface model
(Blackwell Science Ltd and the Eurographics Association, 1993) De Floriani, Leila; Mirra, Daniela; Puppo, Enrico
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.
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, Tomoyuki
Photorealistic 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.
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 Claude
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.
A New Radiosity Approach Using Area Sampling for Parametric Patches
(Blackwell Science Ltd and the Eurographics Association, 1993) Nishita, Tomoyuki; Nakamae, Eihachiro
A high precision illumination model is indispensable for lighting simulation and realistic image synthesis. For the purpose of improving realism, research on global illumination has been done, and several papers on radiosity methods have been presented. In the most recently proposed methods, the shapes of light sources and objects are restricted to polygons or simple curved surfaces. We present a more general method which can handle the kind of free-form surfaces widely used in industrial products and in architecture. The method proposed here solves the problem of the interreflection of light (i.e., radiosities) between patches, and form-factors, which play an important role in this process, are precisely calculated without aliasing through the use of an area sampling method (i.e., pyramid tracing). Furthermore the method can handle both non-uniform intensity curved sources and non-diffuse surfaces.
Pseudo-Satellitefilm Using Fractal Clouds to Enhance Animated Weather Forecasting
(Blackwell Science Ltd and the Eurographics Association, 1993) Sakas, Georgios; Schroder, Florian; Koppert, Hans-Joachim
We have developed a system enabling the National German Meteorological Office to generate pseudo-satellite images and video sequences based on their weather forecasting simulation data. With our system meteorologists can visualize the past and the current weather situation, evaluate their simulation results, and produce animated weather forecast videos broadcasted by several television stations. Realistic images are generated by interpolating the extremely coarse weather simulation data grid and enhancing the result using fractal clouds. It also enables the meteorologists to interactively change the forecast data in order to compensate the lack of accuracy or the known errors in their simulation models. Our system TRITON enables the visualization of complex weather simulations in a more natural way by presenting an intuitively understandable forecast.
A Prototype of a Cooperative Visualization Workplace for the Aerodynamicist
(Blackwell Science Ltd and the Eurographics Association, 1993) Pagendarm, H.-G.; Walter, B.
Several feasibility studies for cooperative visualization were performed based on an existing modular visualization system. Two different architectures for the implementation of a cooperative system were identified, implemented and tested.One architectural model, the broadcast model, assumes either one single visualization system running on a central facility driving multiple displays or in case of cooperative work it assumes that each visualization module drives multiple displays.The second model, the synchronized visualization systems, features distributed visualization tools with synchronization mechanisms. The synchronization ensures that all partners create identical images from identical data. This model requires special control features to avoid conflicts created by user-interaction.Both architectures are complete by adding bi-directional video connection and audio communication over the network plus offering remote cursor functionality.Two prototype implementations were produced to compare the two architectures and to evaluate the feasibility of cooperative visualization on existing hardware. Because of the poor access to wide-area networks, the prototypes were tested in a local area network. Visualization protocols, data communication, video and audio ran on a standard Ethernet based on TCP/IP communications. The tests were done using typical data from aerodynamics or numerical flow simulations.In spite of the limits due to low network bandwidth and slow performance of some hardware components the second architecture using the synchronized systems seems to be useful and feasible even under today s circumstances. There are no additional features identified which would be needed to run the cooperative visualization on a wide area network but a higher network throughput would be required.
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.
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,
Introducing blending operations in feature models
(Blackwell Science Ltd and the Eurographics Association, 1993) Laakko, Timo; Mantyla, Martti
We describe the implementation of a blending facility in the context of a feature modelling system where solid and feature-based modelling operations can be utilized in parallel during the design process of a part. The definition of blends can be done in a graphical user interface by selecting edges to be blended. Feature recognition of blends facilitates the definition process of blends. Alternatively, a special feature editor can be used to add blends to the feature model. The particular implementation style chosen gives rise to aflexible and easy-to-use modelling tool.

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