bluuebunny/crossref_metadata_2025 huggingface dataset:
Automatic Generation of Virtual Woodblocks and Multicolor Woodblock Printing
Authors: Mizuno S. , Kasaura T. , Okouchi T. , Yamamoto S. , Okada M. , Toriwaki J.
Published: March 2003

In this paper, we study a method to synthesize a multicolor virtual woodblock print by using several virtual woodblocks. It consists of two sections: carving and printing, to synthesize a virtual print. In the carving section, virtual woodblocks are generated by a user with supporting of an automatically carving method based on feature extraction of a gray value image. And woodblocks are also generated automatically by using a full‐color image as a draft. In the printing section, a “paper sheet", a “printing brush" and “ink" are prepared in addition to the “woodblock" in the virtual space and the user synthesizes a woodblock print interactively. As the printing factors, a color of ink, a moisture value and a grain change the finish of the print. Using several virtual woodblocks and printing to a paper sheet in succession, a printing image of each woodblock is combined based on the printing factors and a multicolor virtual prints is synthesized.
Scene‐Graph‐As‐Bus: Collaboration between Heterogeneous Stand‐alone 3‐D Graphical Applications
Authors: Zeleznik Bob , Holden Loring , Capps Michael , Abrams Howard , Miller Tim
Published: March 2003

We describe the Scene‐Graph‐As‐Bus technique (SGAB), the first step in a staircase of solutions for sharing software components for virtual environments. The goals of SGAB are to allow, with minimal effort, independently‐designed applications to share component functionality; and for multiple users to share applications designed for single users.This paper reports on the SGAB design for transparently conjoining different applications by unifying the state information contained in their scene graphs. SGAB monitors and maps changes in the local scene graph of one application to a neutral scene graph representation (NSG), distributes the NSG changes over the network to remote peer applications, and then maps the NSG changes to the local scene graph of the remote application. The fundamental contribution of SGAB is that both the local and remote applications can be completely unaware of each other; that is, both applications can interoperate without code or binary modification despite each having no knowledge of networking or interoperability.
Subdivision Surface Tesselation on the Fly using a versatile Mesh Data Structure
Authors: Müller Kerstin , Havemann Sven
Published: March 2003

Subdivision surfaces have become a standard technique for freeform shape modeling. They are intuitive to use and permit designers to flexibly add detail. But with larger control meshes, efficient adaptive rendering techniques are indispensable for interactive visualization and shape modeling. In this paper, we present a realization of tesselation‐on‐the‐fly for Loop subdivision surfaces as part of a framework for interactive visualization.
The Impulse Graph: A New Dynamic Structure For Global Collisions
Authors: Baciu George , Keung Wong Sai
Published: March 2003

In interactive virtual environments and dynamic simulations, collisions between complex objects and articulated bodies may occur simultaneously at multiple points or regions of interference. Many solutions to the collision response problem are formulated based on the local pair‐wise contact dynamics. In this article, we present a new solution to the global interactions and dynamic response between multiple structures in a three‐dimensional environment. This is based on a new dynamic impulse graph that tracks the reaction forces through the entire system and gives a global view of all the interactions in a multibody system.
A Multiresolution Model for Soft Objects Supporting Interactive Cuts and Lacerations
Authors: Ganovelli Fabio , Cignoni Paolo , Montani Claudio , Scopigno Roberto
Published: March 2003

Performing a really interactive and physically‐based simulation of complex soft objects is still an open problem in computer animation/simulation. Given the application domain of virtual surgery training, a complete model should be quite realistic, interactive and should enable the user to modify the topology of the objects. Recent papers propose the adoption of multiresolution techniques to optimize time performance by representing at high resolution only the object parts considered more important or critical. The speed up obtainable at simulation time are counterbalanced by the need of a preprocessing phase strongly dependent on the topology of the object, with the drawback that performing dynamic topology modification becomes a prohibitive issue. In this paper we present an approach that couples multiresolution and topological modifications, based on the adoption of a particle systems approach to the physical simulation. Our approach is based on a tetrahedral decomposition of the space, chosen both for its suitability to support a particle system and for the ready availability of many techniques recently proposed for the simplification and multiresolution management of 3D simplicial decompositions. The multiresolution simulation system is designed to ensure the required speedup and to support dynamic changes of the topology, e.g. due to cuts or lacerations of the represented tissue.
Real Time Local Approximation of Deformations using Rotations
Authors: Maillot Jerome
Published: March 2003

Additional realism can be achieved in computer generated images using smooth and increasingly complex deformations. Though significant effort has been spent on improving these deformations, no general method has been proposed yet to deal with rigid pieces connected to soft objects. This paper proposes a general framework to solve this problem. We will present several types of applications, such as flowing small objects in a deformation field, animating rigid features connected to some deformed object, or smoothly attached limbs to a deforming body. All the calculations presented here can be applied to any type of deformation, provided that the deformation at each point only depends on the point itself. Even though we can directly compute the result for some analytical deformation fields, we will show that a good sampling of the deformation in the area of interest is generally enough. One intermediate result consists of a practical method to find the best rotation that approximates a linear transformation. The proposed method is a superset of the Gram‐Schmidt orthonormalization process, and is much easier to compute than global methods based on Taylor series.
Hierarchical Reconstruction of BRDFs using Locally Supported Functions
Authors: Noé N. , Péroche B.
Published: March 2003

BRDFs are the backbone of realistic rendering algorithms. Analytical models are sometimes ineffective since they frequently cannot represent very particular material characteristics (retro‐reflection, anisotropy, off‐specularity, …). Consequently one might want to use measured BRDF data directly; this leads to solving the problem of BRDF reconstruction. In this paper, we propose a new solution which uses locally supported functions that lead to a hierarchical approach able to take irregular distributions of sampled data into account. This method is not computationally expensive and guarantees a physically valid reconstruction. We also discuss the quality of the reconstruction, introducing some new error parameters.
Displacement Mapping using Scan Conversion Hardware Architectures
Authors: Doggett Michael , Kugler Anders , Straßer Wolfgang
Published: March 2003

This paper presents a novel algorithm and architectures for perspective correct displacement of the surface geometry of a polygonal model using a displacement map. This new displaced surface geometry is passed onto a traditional rendering pipeline. The algorithm uses a multiple pass approach in which the geometry is displaced in the first pass and then the displaced geometry is rendered. The significant features of the algorithm are that the surface is displaced after its triangle mesh is transformed into screen space and that it uses only bi‐linear interpolation for calculating the displaced geometry allowing a cheap incremental scan‐line implementation. A hardware architecture based on this algorithm is presented along with possible alternative implementations. The technique presented here allows greater photorealism by using increased detail without an increase in bandwidth for geometry or calculation time for transformation.
The 3D Model Acquisition Pipeline
Authors: Bernardini Fausto , Rushmeier Holly
Published: March 2003

Three‐dimensional (3D) image acquisition systems are rapidly becoming more affordable, especially systems based on commodity electronic cameras. At the same time, personal computers with graphics hardware capable of displaying complex 3D models are also becoming inexpensive enough to be available to a large population. As a result, there is potentially an opportunity to consider new virtual reality applications as diverse as cultural heritage and retail sales that will allow people to view realistic 3D objects on home computers.

Although there are many physical techniques for acquiring 3D data—including laser scanners, structured light and time‐of‐flight—there is a basic pipeline of operations for taking the acquired data and producing a usable numerical model. We look at the fundamental problems of range image registration, line‐of‐sight errors, mesh integration, surface detail and color, and texture mapping. In the area of registration we consider both the problems of finding an initial global alignment using manual and automatic means, and refining this alignment with variations of the Iterative Closest Point methods. To account for scanner line‐of‐sight errors we compare several averaging approaches. In the area of mesh integration, that is finding a single mesh joining the data from all scans, we compare various methods for computing interpolating and approximating surfaces. We then look at various ways in which surface properties such as color (more properly, spectral reflectance) can be extracted from acquired imagery. Finally, we examine techniques for producing a final model representation that can be efficiently rendered using graphics hardware.
A Graphic Programming Environment Based on KAΔMOΣ
Authors: Dulli Susi , Milanese Vitaliano
Published: March 2003

In this paper the design and development of a graphic programming system to be relied on KAΔMOΣ are described. The system architecture upresented together with the functionality of construction and manipulation of the geometric entities. The environment provides an homogeneous handling of both 2D and 3D objects, these last being represented in a complete solid modelling scheme. Handling is achieved through a set of operators designed to manipulate geometric entities in a way suitable to hide users the implementation details of the specific representation domain. Prolog has been used as a common language to implement both the geometric entities supported by a hierarchical construction and their shape constraints.
A Computer Model For Pinscreen Simulation: A New Animation Paradigm
Authors: Lopes Pedro Faria , Gomes Mario Rui
Published: March 2003

Actual computer image and motion synthesis paradigms are presented in order to introduce a new computer animation paradigm that simulates the traditional pinscreen animation technique. Pinscreen is a very particular and difficult device that enables a “chiaroscuro” approach to image synthesis. The paper describes the traditional pinscreen technique, the way it is operated, results and related difficulties. An extended computer model, including colour and time extensions, to simulate the pinscreen is presented. Results achieved with vector and raster approaches are discussed. Advantages and possibilities of the method when compared with the traditional method and the problems that arise from this technique will also be explained. Finally current and future work is referenced.
The Fractal Nature of an Ecological Model
Authors: Bennan Wang , Yin Shi
Published: March 2003

With the help of computer graphics, the chaotic behaviour of an ecological model in the complex plane has been investigated. Convergence maps that show multi‐fractal characteristics (science) and beautiful patterns (art) are presented.
Trends and Developments in Computational Geometry
Authors: De Berg Mark
Published: March 2003

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.
Rendering NURB Regions For 2D Animation
Authors: Willis Philip , Oddy Robert
Published: March 2003

We describe an accurate method of rendering by scan‐conversion of closed regions bounded by NURBs, with particular comments on its application to computer‐based 2D animation. It is shown that the method is fast, analytically accurate, and can be readily extended to include anti‐aliasing and clipping.
An Object‐Oriented View of the User Interface
Authors: Zhou Tom Z.‐Y. , Kubitz William J.
Published: March 2003

The object‐oriented view of the user interface presented here is a model of object responsibilities‐sharing and cooperation for a typical user interface. The model regards the user interface as a three‐layer architecture, with the application contributing to one of the layers called the application exposure, The model seeks to promote user interface software reuse by coupling the user interface and the application with well‐defined message protocols, by properly allocating user interfacefunctions to the layers so as to reduce and discipline their dependencies, and byfactoring complex abstractions into reusable secondary components.
The Visualization Input Pipeline ‐ Enabling Semantic Interaction in Scientific Visualization
Authors: Felger W. , Schröder F.
Published: March 2003

Scientific Visualization systems are primarily output‐oriented, Users can specify and change parameters that are controlling the visualization process, which will result in different data representations or images respectively. But no mechanism is provided to really interact with the application data (semantic interaction) that has been changed step by step by the process of visualization.

In this paper general concepts are elaborated and presented to achieve semantic interaction in dataflow environments for Scientific Visualization.
Fast Generation and Surface Structuring Methods for Terrain and Other Natural Phenomena
Authors: Koh Eng‐Kiat , Hearn D. D.
Published: March 2003

Fractal geometry has proven to be a powerful tool for modeling natural phenomena. Using discrete approximations to fractional Brownian motion over a finite grid plane, computer graphics terrain‐rendering algorithms are able to generate highly realistic topographical displays. Similar procedures can be applied to model other natural phenomena, such as clouds and water. Two important considerations in these algorithms are computational efficiency and the ability to control macroscopic surface features. Here we introduce a technique for structuring surface features so as to conform to a specified “elevation” envelope. We also present methods for implementing this technique using a recursive random midpoint‐displacement procedure.
The Parametric Differential Method: An Alternative to the Calculation of Form Factors
Authors: Baranoski Gladimir V. Guimaraes
Published: March 2003

The parametric differential method calculates the form factors without using approximations by polygons. Because of this it contributes to the improvement of the realism of the images synthesised through the radiosity method. This paper presents the most important characteristics of the parametric differential method as well as the results concerning its accuracy. Comparison of the form factors found using the new algorithm has been made with those analytically found.
An adaptive Discretization Method For Radiosity
Authors: Languenou Eric , Bouatouch Kadi , Tellier Pierre
Published: March 2003

When using radiosiiy, the visual quality of the rendered images strongly depends on the method employed for discretizing the scene into patches. A too fine discretization may give rise to artifacts, while with a coarse discretization areas with high radiosity gradient may appear. To overcome these problems, the discretization must adapt to the scene. That is, the interaction between two patches must account for the distance between them as well as their surface area. In other words, surfaces far away are discretized less finely than nearby surfaces. These aspects are considered by the new adaptive discretiration method described in this paper. It performs both discretization and system resolution at each iteration of the shooting process, allowing then interactivity.
A Run‐Length Slice Line Drawing Algorithm without Division Operations
Authors: Fung Khun Yee , Nicholl Tina M. , Dewdney A. K.
Published: March 2003

Of the two major approaches to line drawing, run‐length slice algorithms are seldom used because of the division operation deemed necessary in these algorithms. The biggest advantage of these algorithms, the reduction of additions used, is considered outweighed by the division used. In this paper, a new run‐length slice algorithm that does not require a division operation is presented. Furthermore, it uses the double‐stepping paradigm in incremental line drawing algorithms to reduce the number of additions used by at least half.

For sufficiently long lines, this algorithm uses at least 50% fewer arithmetic operations than Wu et al.'s bi‐directional double‐step incremental algorithm. But because of its high initialization cost, for short lines, it is less efficient. For a line with endpoints (0,0) and (δx, δy), the strategy is then to use the bi‐directional Bresenham algorithm for very short lines (δx < 20), the bi‐directional double‐step algorithm for moderate long lines (20 ≤δx ≤ 110), and the new algorithmfor the longer lines (δx > 110).
Equidistant Smoothing of Polyhedra with Arbitrary Topologies
Authors: Ma Lizhuang , Liang Youdong , Peng Qunsheng
Published: March 2003

Smoothing of polyhedron with arbitrary topology is an important issue in CAGD and CAD/CAM, but so far it is deemed to be difficult to smooth the complex corners of a polyhedron. In this paper, the concept of distance surfaces of a surface and a solid is introduced, and the incisive properties of such surfaces are addressed which provide a theoretical foundation for modifying a general corner. The method is based on making constricted volume and the maximum distance the volume can be constricted is given too. It is shown that by the proposed method in this paper any polyhedron can be G1 smoothed with quadraic and, sometimes toroidal surfaces. The new approach is suitable for engineering design and NC machining. The associated algorithm based on the classification theorem of corners is simple, fast and robust.
A Simple Description of Complex Curves
Authors: Bouras A. , Shariat B. , Vandorpe D.
Published: March 2003

In this paper, we propose a method of complex curves description, based on the use of standard primitives (curve arcs), inscribed in including boxes. This method simplifies the creation steps (curves are not defined with the help of control points), and the manipulation steps (using including boxes).

This study constitutes an extension to our descriptive universal language, named “G”, which is used in a general desig n environment, permitting the integration of various models (solids1, polyhedrons2, surfaces3 and fractals), in order to offer the adequate tools adapted to the problems to be solved, in a unique modeller.
Interactive Shape Control of Interpolating B‐splines
Authors: Krokos M. A. , Slater M.
Published: March 2003

This paper presents a new methodfor providing interactive shape control of interpolating B‐splines. The CAD designer can directly interact with geometric entities defined on the B‐spline at any interpolated data point; shape adjustments can be performed either globally or locally. Our approach is based on Bλ‐splines of order k (λ,k ≥1), i.e. λ‐reparametrized, classical B‐splines. The method presented can be easily generalised to surfaces defined either as tensor products or by using the skinning technique; interactive shape control can be provided in both surface parametric directions.
Combined Direct and Inverse Kinematic Control for Articulated Figure Motion Editing
Authors: Boulic Ronan , Thalmann Daniel
Published: March 2003

A new approach for the animation of articulated figures is presented. We propose a system of articulated motion design which offers a full combination of both direct and inverse kinematic control of the joint parameters. Such an approach allows an animator to specify interactively goal‐directed changes to existing sampled joint motions, resulting in a more general and expressive class of possible joint motions. The fundamental idea is to consider any desired‐joint space motion as a reference model inserted into the secondary task of an inverse kinematic control scheme. This approach profits from the use of half‐space Cartesian main tasks in conjunction with a parallel control of the articulated figure called the coach‐trainee metaphor. In addition, a transition function is introduced so as to guarantee the continuity of the control. The resulting combined kinematic control scheme leads to a new methodology of joint‐motion editing which is demonstrated through the improvement of a functional model of human walking.
Consistent Schemes for Addressing Surfaces when Ray Tracing Transparent CSG Objects
Authors: Gervautz Michael
Published: March 2003

Constructive Solid Geometry (CSG) defines the shape of objects, i.e. the inside and the outside regions of objects, but it does not define the material properties of the space in the interior of objects. The definition is ambiguous. There are points of space lying in several primitives, which can consist of different materials. When visualizing transparent objects this ambiguity leads to strange results, which are not consistent with the CSG modelling scheme and must therefore be eliminated. This work describes how an unambiguous model can be built by asymmetric CSG‐operators and how correct refraction and shading on material boundaries can be established by separating surface properties from material properties. This separation leads to a consistent view of CSG modelling also concerning materials and surfaces. Ray tracing CSG trees and the shading model are influenced by these asymmetric operators. We introduce an applied classification scheme to handle the requirements of the new operator definition.
Verve
Authors: Knittel Günter
Published: March 2003

The design principles of a hardware acceleratorfor volume rendering are described. The architecture represents a voxel subsystem which interfaces easily to any existing workstation. Host requirements are low since it contains a multiport memory holding the complete data set and all arithmetic units needed to perform an effective visualization.

Our approach aims at virtual reality by providing some “real‐world” examination techniques. The user (e.g., a physician) is enabled to analyze the data set from an arbitrary viewpoint and, even more, to “walk through” the volume model. For a realistic impression, the machine produces perspective projections, supports the illumination by non‐parallel light comingfrom a freely movable point light source and provides depth cueing. The objects are Phong shaded at a rate of 107 operations/s and can be displayed semitransparently. One unit achieves interactive speed: for real‐time operation only a small number of units (typically 4‐16) must be placed in parallel.
Interactive Neural Network Texture Analysis and Visualization for Surface Reconstruction in Medical Imaging
Authors: Busch C. , Groß M.H.
Published: March 2003

The following paper describes a new approach for the automatic segmentation and tissue classification of anatomical objects such as brain tumors from magnetic resonance imaging (MRI) data sets using artificial neural networks. These segmentations serve as an input for 3D–reconstruction algorithms. Since MR images require a careful interpretation of the underlying physics and parameters, we first give the reader a tutorial style introduction to the physical basics of MR technology. Secondly, we describe our approach that is based on a two–pass method including non–supervised cluster analysis, dimensionality reduction and visualization of the texture features by means of nonlinear topographic mappings. An additional classification of the MR data set can be obtained using a post–processing technique to approximate the Bayes decision boundaries. Interactions between the user and the network allow an optimization of the results. For fast 3D–reconstructions, we use a modified marching cubes algorithm but our scheme can easily serve as a preprocessor for any kind of volume renderer.

The applications we present in our paper aim at the automatic extraction and fast reconstruction of brain tumors for surgery and therapy planning. We use the neural networks on pathological data sets and show how the method generalizes to physically comparable data sets.
Storage Support for Multidimensional Discrete Data in Multimedia Databases
Authors: Furtado Paula , Teixeira Jose Carlos
Published: March 2003

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.
Updating Polygonizations*
Authors: Abellanas M. , Garcia J. , Hernbández G. , Hurtado F. , Serra O. , Urrutia J.
Published: March 2003

In this paper we consider polygonizations that are robust when faced with changes in the vertices that are present or in their position. We analyze the dynamic maintenance of different types of polygonizations (monotone, star‐shaped…) and we introduce monotone half‐convex polygonizations that are specially interesting because they provide minimum cost per insertion or deletion. If we had to delete not only one point but several external layers of the set, then the onion polygonizations would be suited, because they can be updated in constant time. We also consider the case of points that can be moved to contiguous positions and we show how to polygonize the set for updating in linear time. We deal too with security problems for a polygon: What is the maximum distance the vertices of a polygon could be moved away of their position in such a way that the topology on the boundary of the polygon (or its convexity) remains the same?.
Introducing blending operations in feature models
Authors: Laakko Timo , Mäntylä Martti
Published: March 2003

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.
Direct 3D Manipulation Techniques for Interactive Constraint‐based Solid Modelling
Authors: Fa Mingxian , Fernando Terrence , Dew Peter M.
Published: March 2003

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.
Extracting contour lines from a hierarchical surface model
Authors: De Floriani Leila , Mirra Daniela , Puppo Enrico
Published: March 2003

The Hierarchical Triangulated Irregular Network (HTIN) is a structure for representing 2½‐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.
A 4D Ray Tracing
Authors: Maurel Herve , Duthen Yves , Caubet René
Published: March 2003

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.
DaScript3D Integrating 3D Graphics in a Page Description Language
Authors: Samara Veronika
Published: March 2003

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.
Pseudo‐Satellitefilm Using Fractal Clouds to Enhance Animated Weather Forecasting
Authors: Sakas Georgios , Schröder Florian , Koppert Hans‐Joachim
Published: March 2003

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.
Photo‐Realistic Imaging of Digital Terrains
Authors: Cohen Daniel , Shaked Amit
Published: March 2003

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.
A New Radiosity Approach Using Area Sampling for Parametric Patches
Authors: Nishita Tomoyuki , Nakamae Eihachiro
Published: March 2003

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.
Form Factor Calculation: a New Expression with Implementations on a Parallel T.Node Computer
Authors: Michelin Sylvain , Maffeis Gualtiero , Arquès Didier , Grossetie Jean Claude
Published: March 2003

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.
Variational Surface Design and Surface Interrogation
Authors: Hagen H. , Hahmann St. , Bonneau G.‐P.
Published: March 2003

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.
Quality Control of an Interpolation Method for Discontinuous Parametric Surfaces
Authors: Seron F.J. , Torrens J.J , Magallon J.A.
Published: March 2003

In this paper we study a finite element interpolation method for fitting discontinuous parametric surfaces when the data points are the nodes of a curvilinear grid. Quality control of the interpolating surfaces is also considered, focussing on the display of isophotes and reflection lines using ray tracing techniques. Finally, graphical and numerical examples are given.
A Prototype of a Cooperative Visualization Workplace for the Aerodynamicist
Authors: Pagendarm H.‐G. , Walter B.
Published: March 2003

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 Determination of Form‐Factors by Lookup Table
Authors: Sun Jizhou , Zou L.Q. , Grimsdale R.L.
Published: March 2003

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.
Ray Tracing an Octree: Numerical Evaluation of the First Intersection
Authors: Gargantini I. , Atkinson H. H.
Published: March 2003

An algorithm is presented which finds the first intersection of a directed semi‐infinite straight‐line (called ray) with an octree, without resorting to the evaluation of neighbouring nodes. Given a pointer‐based region octree, intersections of the ray with a node's bisecting planes are first evaluated to determine in which sub‐octants the ray‐node intersections may lie; a local ordering then determines the sequence in which these sub‐octants should be examined so that the intersection closest to the ray's origin can be selected.

This idea is applied recursively starting from the root of the octree; the novelty of the approach consists of the fact that the choice of each node's child in the octree is directly derived from the intersection of the ray‐segment within the tested sub‐octant, thus avoiding searching for any neighbouring nodes. The problem of selecting the correct octant while using the commonly available floating‐point arithmetic is also addressed in a ray tracing environment. Comparisons of this approach with the method given by Samet17 are carried out in a variety of cases involving millions of voxels. The improvement ranged from 32% to 62% in terms of execution time.
ANIMA: An Interactive Tool for Scientific Data Animation
Authors: Moltedo Laura , Morigi Serena
Published: March 2003

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.
Graphic Objects: A Mathematical Abstract Model for Computer Graphics
Authors: Torres J.C. , Clares B.
Published: March 2003

This paper defines an abstract mathematical model for graphic systems which incorporates modelling operations. The model is based on the “graphic object” concept. A graphic object is an abstraction of a graphic entity. Graphic objects are a generalization of the Fiume graphic object concept, supporting modelling operations, which give the set of graphic objects an algebraic structure of vector space and booelan algebra. Fiume visualization formalism can be applied to graphic objects. Further, product operations of graphic objects are defined, which are a generalization of solid sweep operations. Graphic object products may be used to build common 2D and 3D objects such as triangles, squares, cubes, circles and spheres from lines and arcs.
Controllable Locality in C2 Interpolating Curves by B2‐splines / S‐splines
Authors: Kuroda Mitsuru , Furukawa Susumu , Kimura Fumihiko
Published: March 2003

This paper presents a systematic scheme for controlling the local behaviour of C2 interpolating curves, based on the cubic B2‐splines and the quartic S‐splines. Both splines have an additional control point obtained by knot‐ insertion or degree‐elevation in each span of the conventional uniform cubic interpolating B‐splines. The shape designer can choose the desired range of locality for each span and get the corresponding additional control point as a barycentric combination of interpolation points within the range, without solving any variational problem and simultaneous equations. The scheme is consistent over the entire curve subject to some typical end conditions. The class of the curves derived includes the conventional cubic interpolating B‐splines. Examples demonstrate the behaviour of the new interpolating curves and the capability of the scheme.
Five‐dimensional Adaptive Subdivision for Ray Tracing
Authors: Simiakakis G. , Day A. M.
Published: March 2003

This paper presents a directional subdivision method for speeding up ray tracing. This method is easy to use, because it automatically adapts the subdivision to the scene relieving the user from having to set parameters for the subdivision. It also attempts a balance between 5D and spatial subdivision in order to benefit from both methods. A memory saving scheme is introduced and experimental results are presented.
Constant‐Time Filtering by Singular Value Decomposition†
Authors: Gotsman Craig
Published: March 2003

We present a technique implementing space‐variant filtering of an image, with kernels belonging to a given family, in time independent of the size and shape of the filter kernel support. The essence of our method is efficient approximation of these kernels, belonging to an infinite family governed by a small number of parameters, as a linear combination of a small number k of “basis” kernels. The accuracy of this approximation increases with k, and requires O(k) storage space. Any kernel in the family may be applied to the image in O(k) time using precomputed results of the application of the basis kernels. Performing linear combinations of these values with appropriate coefficients yields the desired result. A trade off between algorithm efficiency and approximation quality is obtained by adjusting k.

The basis kernels are computed using singular value decomposition, distinguishing this from previous techniques designed to achieve a similar effect. We illustrate by applying our methods to the family of elliptic Gaussian kernels, a popular choice for filtering warped images.
COMPUTER GRAPHICS AND REMOTE SENSING – A SYNTHESIS FOR ENVIRONMENTAL PLANNING AND CIVIL ENGINEERING
Authors: Graf K.Ch. , Suter M. , Hagger J. , Nüesch D.
Published: March 2003

This paper presents efforts undertaken in the field of photo‐realistic visualization of natural landscapes using digital elevation models (DEM) and images generated by remote sensing techniques. The remote sensing systems used in this work include Landsat Thematic Mapper, SPOT HRV and aerial photographs. After an appropriate preprocessing, including radiometric corrections and image enhancement procedures, a precise geometric correction is performed in order to achieve a very high co‐registration of the images with the elevation model. A mosaic of several images at various resolutions is stored together with the DEM in a data set covering an extensive area. These data are then input to an efficient hardware‐independent terrain rendering algorithm based on a forward projection. Atmospheric effects can be simulated. The concept of a virtual scene allows an automated embedding of raytraced 3D objects. The results show that these methods can be used in the field of environmental planning, civil engineering and other applications where terrain visualization is required.