- EG1991 Proceedings (Technical Papers)

# EG1991 Proceedings (Technical Papers)

## Permanent URI for this collection

Continuation Methods for Approximating Isovalued Complex Surfaces

[meta data] [files: ]

Zahlten, Cornelia

;

Jürgens, Hartmut

FACES: Facial Animation, Construction and Editing System

[meta data] [files: ]

Patel, Manjula

;

Willis, Philip J.

Sampling and Anti-Aliasing of Discrete 3-D Volume Density Textures

[meta data] [files: ]

Sakas, Georgios

;

Gerth, Matthias

Refinement criteria for adaptive stochastic ray tracing of textures

[meta data] [files: ]

van Walsum, Theo

;

van Nieuwenhuizen, Peter R.

;

Jansen, Frederik W.

Constructive Cubes: CSG Evaluation For Display Using Discrete 3-D Scalar Data Sets

[meta data] [files: ]

Breen, David E.

Liberation from Flatland: 3D Interaction Based on the Desktop Bat

[meta data] [files: ]

Slater, Mel

;

Davison, Allan

Validity Issues for Modular Boundary Models

[meta data] [files: ]

Bruzzone, Elisabetta

;

De Floriani, Leila

Low Sampling Densities using a psychovisual approach

[meta data] [files: ]

Bouville, Christian

;

Tellier, Pierre

;

Bouatouch, Kadi

Using temporal and spatial coherence for accelerating the calculation of animation sequences

[meta data] [files: ]

Gröller, Eduard

;

Purgathofer, Werner

Configurable Representations in Feature-based Modelling

[meta data] [files: ]

Falcidieno, B.

;

Giannini, F.

;

Porzia, C.

;

Spagnuolo, M.

A Testbed for Architectural Modeling

[meta data] [files: ]

Hall, Roy

;

Bussan, Mimi

;

Georgiades, Priamos

;

Greenberg, Donald P.

Construction Techniques of Graphic, Direct-Manipulation User Interfaces

[meta data] [files: ]

Preea, Wolfgang

;

Pornberger, Gustav

;

Sikora, Hermann

MOVE-X: A System for Combining Video Films and Computer Animation

[meta data] [files: ]

Ertl, Gerhard

;

Müller-Seelich, Heimo

;

Tabatabai, Behnam

An Algorithm of hidden Surface Removal based on Frame-To- Frame Coherence

[meta data] [files: ]

Tost, Daniele

Timewarps: A Temporal Reparameterization Paradigm for Parametric Animation

[meta data] [files: ]

Smith, Jeff

;

Drewery, Karin

Several approaches to implement the merging step of the split and merge region segmentation

[meta data] [files: ]

Popovic, M.

;

Chantemargue, F.

;

Canals, R.

;

Bonton, P.

Integrating Inheritance and Composition in an Objective Presentation Model for Multiple Media

[meta data] [files: ]

Took, Roger

Constructive Page Description Opening Up the Prepress World

[meta data] [files: ]

Samara, Veronika

;

Wiedling, Hans-Peter

Serial cuttings matching: An application to muscle fiber characterization

[meta data] [files: ]

Buche, Patrice

A Symmetrical Input/Output Model

[meta data] [files: ]

Carlsen, Niels Vejrup

;

Christensen, Niels Jorgen

Geometric Modelling from Range Image Data

[meta data] [files: ]

Schmitt, Francis

;

Cken, Xin

;

Du, Wen-Hui

Animation of Landscapes Using Satellite Imagery

[meta data] [files: ]

Geymayer, Barbara

;

Prantl, Manfred

;

Müller-Seelich, Heimo

;

Tabatabai, Behnam

Interrogation of Offsets of Polynomial Surface Patches

[meta data] [files: ]

Vafiadou, Maria - Eleni

;

Patrikalakis, Nicholas M.

Tessellation of Curved Surfaces under Highly Varying Transformations

[meta data] [files: ]

Abi-Ezzi, Salim S.

;

Shirman, Leon A.

Computational Physics : A Modeler - Simulator for animated physical Objects

[meta data] [files: ]

Luciani, Annie

;

Jimenez, Stephane

;

Florens, Jean Loup

;

Cadoz, Claude

;

Raoult, Olivier

A Testbed for Image Synthesis

[meta data] [files: ]

Trumbore, Ben

;

Lytle, Wayne

;

Greenberg, Donald P.

Solid-Interpolating Deformations: Construction and animation of PIPs

[meta data] [files: ]

Kaul, Anil

;

Rossignac, Jarek

Variable-Radius Blending by Using Gregory Patches in Geo- metric Modeling

[meta data] [files: ]

Harada, T.

;

Konnoa, K.

;

Chiyokura, H.

## Browse

### Recent Submissions

Item Combining Volume Rendering with Line and Surface Rendering(Eurographics Association, 1991) Frühauf, MartinShow more Volume data is discrete sampled data in the three-dimensional space. Volume rendering is defined as volume visualization directly from volume primitives and not via surface primitives. Geometric objects are represented as a list of vertices and connecting lines or surface patches. Independent algorithms for rendering the two different categories of data are used. The system, proposed here, combines the results of the different algorithms in one image. A set of common parameters influencing both rendering algorithms and ensuring the consistency of the resulting merged image is identified. A volume rendering algorithm capable to produce the information to be merged is described in detail. The system is able to handle opaque and translucent objects by merging lists of image space elements. The independence of the both rendering modules allows to employ a wide range of algorithms for rendering of geometric objects, even rendering in hardware.Show more Item Continuation Methods for Approximating Isovalued Complex Surfaces(Eurographics Association, 1991) Zahlten, Cornelia; Jürgens, HartmutShow more Basically there are two different approaches for rendering isovalued surfaces in 3D space: projection methods and surface reconstruction. We are discussing two algorithms of the second kind. Both use continuation methods for efficiently scanning an isovalued surface. A simplicial pivoting algorithm by Ralf Widmann which continues earlier work of E. L. Allgower et al., is compared to an approach which is based on subdividing space into cubes. The algorithms determine all simplices or cubes intersecting the surface and then generate an oriented polygonal approximation. For demonstration and comparison we use several fractal and some smooth surfaces. These surfaces are implicitely defined by a function, but it is also possible to apply both methods to 3D volume data.Show more Item FACES: Facial Animation, Construction and Editing System(Eurographics Association, 1991) Patel, Manjula; Willis, Philip J.Show more The aim of the Facial Animation, Construction and Editing System (FACES) is to provide a software simulation of the human face. Attention has focused on the face as an important means of non-verbal communication. The interactive composition and modification of the human head and its subsequent animation, have been identified as being of particular interest. The novelty of FACES is that it integrates the modelling and animation of faces using a three-layer anatomical model. FACES consists of four sub-systems: CONSTRUCT, MODIFY, ANIMATE and RENDER. The CONSTRUCT and MODIFY sub-systems enable changes to be made to the structure of the head, at both global and local levels, enabling specific faces to be created. The ANIMATE sub-system caters for motion specification and control, so that real and exaggerated facial expressions can be animated. The RENDER part of the system facilitates the generation of realistic images and their real-time playback. In this paper we consider the system from the user's point of view, examining the facilities which are provided, their appropriateness and practicality.Show more Item Colour Illustrations(Eurographics Association, 1991) -Show more Item Sampling and Anti-Aliasing of Discrete 3-D Volume Density Textures(Eurographics Association, 1991) Sakas, Georgios; Gerth, MatthiasShow more In recent years, a number of techniques have been developed for rendering volume effects (haze, fog, smoke, clouds, etc.) in order to enhance reality in computer-generated imagery as well as to improve the performance of flying, ship, and driving optical simulators. For modeling such effects, volume 'density' objects are used, which are defined by their density distribution in 3-D space. For such a description a three-dimensional voxel field (solid texture) is usually used. Since we deal with 3-D textures, the methods used for sampling 2-D pixel fields cannot always be employed. In this paper, we propose two variants of a new technique for sampling and anti-aliasing 3-D density voxel fields. First, we point out the problems which occur when such 3-D textures are sampled, especially when the point sampling Monte-Carlo method is used. 'Distance sampling' and 'pyramidal-volume sampling' are then introduced. The first ,technique samples the texture along a straight line defined by the eye position and the pixel midpoint, whereas the pyramidalvolume technique approximately samples the volume of the pyramid defined by the eye and the four pixel comers. In comparison to other existing methods, both methods greatly reduce aliasing and calculation time. Especially the second one provides a constant-time filtering, whereby minimizing the number of texture evaluations. In the last paper section we demonstrate the applicability of the proposed methods for animation as well as for visualization purposes.Show more Item Refinement criteria for adaptive stochastic ray tracing of textures(Eurographics Association, 1991) van Walsum, Theo; van Nieuwenhuizen, Peter R.; Jansen, Frederik W.Show more Adaptive stochastic ray tracing is a rendering technique that generates high-quality anti-aliased images by sampling the image in a non-regular pattern that is adaptively refined. Image refinement can be guided by image space or object space criteria. For display of textures, additional criteria that operate in texture space can be added to further improve image quality. In this paper three texture space refinement criteria are introduced. The methods minimize the chance of sampling errors at the cost of only a small amount of preprocessing and are comparable in efficiency with existing texture prefiltering methods.Show more Item Constructive Cubes: CSG Evaluation For Display Using Discrete 3-D Scalar Data Sets(Eurographics Association, 1991) Breen, David E.Show more The algorithm presented in this paper converts a CSG model into a representation for interactive display on an engineering workstation. Called Constructive Cubes, the algorithm extends the standard CSG-point classification algorithm and then employs a popular isosurface generation algorithm, Marching Cubes, to generate a list of polygons that approximates the surface of a CSG model. The polygons may then be interactively displayed, shaded and inspected on a workstation. The algorithm has many advantages over other CSG algorithms. It is straightforward to implement, requiring no complex surface intersection calculations. The algorithm provides an inherent flexibility that allows a user to balance the time/quality trade-off. It is designed to take advantage of current and future advances in both visualization and engineering workstation design.Show more Item Declarative Graphics And Dynamic Interaction(Eurographics Association, 1991) Johnson, C.W.; Harrison, M.D.Show more First order logic provides a means of integrating the specification and prototyping of interactive systems. It can describe graphical images in a declarative and order independent manner. It supports the definition of abstract devices which avoid the complexity of representing ‘raw’ input from a variety of physical devices. The following pages show how such techniques must be extended in order to prototype and reason about dynamic interaction with graphical interfaces. The incorporation of a temporal ordering into logical specifications provides a means of describing changes in the structure of graphical images. It can also identify the sequencing which may be implicit within specifications of interactive dialogues. This paper describes how PRELOG, a tool for Presenting and REndering LOGic specifications of interactive systems, has been extended to include a temporal logic interpreter.Show more Item Liberation from Flatland: 3D Interaction Based on the Desktop Bat(Eurographics Association, 1991) Slater, Mel; Davison, AllanShow more A novel device for 3D interaction is introduced, the Desktop Bat. This device is an evolutionary development of a mouse. It is like a mouse in that it is used on a desktop, but provides 5 degrees of freedom since in conjunction with translations it can be used to effect rotations about any combination of the principal axes. We discuss the requirements for 3D interaction which led to the design of the Desktop Bat, and the interaction models and software which allow it to be used as a 6 degrees of freedom input device.Show more Item Validity Issues for Modular Boundary Models(Eurographics Association, 1991) Bruzzone, Elisabetta; De Floriani, LeilaShow more Modular boundary models are a class of solid models which describe a solid object as a collection of face-abutting object parts, called components. The Face-to-Face Composition (FFC) model is a specific model of this class, which encodes both the connection and the interference information among object components. Necessary and sufficient conditions for an FFC model to be valid are defined in terms of a representation of the FFC model, called the FFC graph. The problem of producing valid FFC models from the decomposition of the FFC model of a given object into subobjects is studied in connection with the generation of a production graph.Show more Item Discrepancy as a Quality Measure for Sample Distributions(Eurographics Association, 1991) Shirley, PeterShow more Discrepancy, a scalar measure of sample point equidistribution, is discussed in the context of Computer Graphics sampling problems. Several sampling strategies and their discrepancy characteristics are examined. The relationship between image error and the discrepancy of the sampling patterns used to generate the image is established. The definition of discrepancy is extended to non-uniform sampling patterns.Show more Item A DDA Octree Traversal Algorithm for Ray Tracing(Eurographics Association, 1991) Sung, KelvinShow more A spatial traversal algorithm for ray tracing that combines the memory efficiency of an octree and the traversal speed of a uniform voxel space is described. A new octree representation is proposed and an implementation of the algorithm based on that representation is presented. Performance of the implementation and other spatial structure traversal algorithms are examined.Show more Item Low Sampling Densities using a psychovisual approach(Eurographics Association, 1991) Bouville, Christian; Tellier, Pierre; Bouatouch, KadiShow more It has long been observed that the keenness of sight is lower for diagonal directions than for horizontal or vertical ones. This anisotropy of the human eye response can be exploited by using a non-orthogonal sampling pattern with a reduced sampling density. After an introduction to the two-dimensional sampling theory, it is shown that quincunx sampling is well suited to this characteristic. Then a sampling scheme based on this approach is described. This effectively leads to halving the sampling density and thereby the computing time of ray-traced pictures.Show more Item Using temporal and spatial coherence for accelerating the calculation of animation sequences(Eurographics Association, 1991) Gröller, Eduard; Purgathofer, WernerShow more Ray tracing is a well known technique for generating realistic images. One of the major drawbacks of this approach are the extensive computational requirements for image calculation. When generating animation sequences frame by frame the computational cost might easily become intolerable. In the last years several methods have been devised for accelerating the computational speed by using spatial and temporal coherence. While these techniques work only under certain restrictions, a new approach is presented in this paper which leads to a considerable speed-up of the calculation process without putting any limitations on camera or object movement. In principle, the method is an extension of /ArKi87/, where rays are considered points in 5D space, by the time dimension. CSG is used for object description and has been modified correspondingly to allow easy use of coherence properties. The paper describes the theoretical background and the main concepts of a practical implementation.Show more Item Configurable Representations in Feature-based Modelling(Eurographics Association, 1991) Falcidieno, B.; Giannini, F.; Porzia, C.; Spagnuolo, M.Show more A double description is proposed for the representation of a feature-based model which supports the distinction between form and functionality. This description consists of a primary representation in terms of geometric features ( geometric feature graph) and a set of feature-based representations which are created by transformations that are viewpoint specific and apply to the geometric feature graph.Show more Item A Testbed for Architectural Modeling(Eurographics Association, 1991) Hall, Roy; Bussan, Mimi; Georgiades, Priamos; Greenberg, Donald P.Show more This paper describes the philosophy and implementation of a modeling system that is easy to use yet addresses some of the difficulties of design. It does this by supporting concurrent schematic and geometric representations, alternative solution schemes, ambiguous and incomplete specification, and multiple levels of detail through a wide range of scale. The system treats an object as a hierarchical record of design decisions and treats geometry as an artifact of traversing a decision tree. For displaying geometry, the system incorporates fast rendering techniques for interactive use and global illumination algorithms for design evaluation and final presentation. The system is intended to serve as an extensible testbed for long-term research in modeling and design. Vigorous use by students in the Department of Architecture at Cornell is the vehicle for system evaluation and redirection of research goals.Show more Item Construction Techniques of Graphic, Direct-Manipulation User Interfaces(Eurographics Association, 1991) Preea, Wolfgang; Pornberger, Gustav; Sikora, HermannShow more This paper deals with human-computer interaction in several ways. On the one hand it presents the roots of interactive, graphic user interfaces and how such interfaces are implemented on the abstraction level of programming languages: The construction of graphic, direct-manipulation interfaces with conventional programming techniques is compared with an object-oriented approach based on powerful class libraries (called user interface application frameworks). Although application frameworks substantially ease the building of highly interactive applications the abstraction level is considered to be too low to support prototyping such interfaces in a comfortable way. Hence we portray DICE1 (Dynamic Interface Creation Environment), a tool for prototyping graphic user interfaces implemented itself in an object-oriented manner. In particular this paper discusses the question of how dynamic behavior can be added to a user interface prototype. It also presents a useful and powerful way to combine conventionally developed and object-oriented software systems.Show more Item MOVE-X: A System for Combining Video Films and Computer Animation(Eurographics Association, 1991) Ertl, Gerhard; Müller-Seelich, Heimo; Tabatabai, BehnamShow more The objective of the presented project was to implement a system for the visualization of buildings. The system is used to create movies of buildings and interior rooms before they are built. For a realistic impression of a building it is very important to show its actual environment in the film. The designed software solution permits to create films where real images of the environment are overlaid with computer generated images of the building. In order to overlay the video film with computer generated images, it is necessary to compute the exact position, the viewing direction and the adjustment of the zoom for every frame of the film. These parameters can be calculated from the video images. This paper describes the algorithms used to calculate the camera parameters and to track passpoints in a sequence of video images. Some problems resulting from interlaced video and low resolution are discussed in detail. The rendering techniques used to generate images of the new building are also discussed.Show more Item Shading with Area Light Sources(Eurographics Association, 1991) Tanaka, Toshimitsu; Takahashi, TokiichiroShow more This paper derives a shading model for area light sources which covers both diffuse and specular reflection. The shading model assumes ideally diffuse polygonal light sources and uses Phong’s reflection model. The model can accurately integrate the intensities of diffuse and specular reflection without simulating an area light source as an array of point light sources. To simplify the reflection integration, each light source is transformed from the Cartesian coordinate system into the polar system. The light source is projected onto a unit sphere and then triangulated along great circles of the unit sphere. Finally, the integration value is calculated by polynomial approximation. Since our method can accurately integrate both diffuse and specular reflection, it can generate images that are more photorealistic than conventional methods. Because point light sources are not employed, highlight roughness is completely suppressed. Several images are presented that show the advantages of our method.Show more Item An Algorithm of hidden Surface Removal based on Frame-To- Frame Coherence(Eurographics Association, 1991) Tost, DanieleShow more Frame-to-frame coherence capitalizes on the continuity existing between successive frames in order to predict the visibility of the scene at a given instant on the basis of its visibility at the previous instant. It is shown that all the algorithms based on frame-to-frame coherence share a common model and involve similar data structures. This model is used as a framework for a discussion of possible frame-to-frame coherence algorithms. A specific solution based on a partition of the image space into several 2-D regions is then presented. A temporal graph of the depth priority relationship of the objects is first computed in a pre-process along with a temporal BSP tree of each object. In the first frame a total traversal of both data structures is required in order to establish the priority list of the faces of the scenes. In successive frames, the priority list is easily updated with partial traversals and with no geometrical computations. The complexity of the proposed algorithm is discussed. Some examples are presented with comments on the results of their implementation.Show more Item Timewarps: A Temporal Reparameterization Paradigm for Parametric Animation(Eurographics Association, 1991) Smith, Jeff; Drewery, KarinShow more The ability to reparameterize the temporal axis in an animated sequence is a powerful and underexplored tool. Timewarps are described as extensions to previous work and the advantages of this tool are outlined. Timewarps allow an animator to progressively refine the timing of all or part of an animation. Problems inherent to this new concept were brought to light by the authors' implementation and are described in terms of both user interface and development issues. Solutions are discussed and directions for further study are outlined.Show more Item Interactive Conformance Testing for PHIGS(Eurographics Association, 1991) Cugini, John V.Show more Conformance testing for the Programmer’s Hierarchical Interactive Graphics System (PHIGS) standard presents certain novel difficulties, especially the indirect effect of many functions, and the inaccessibility to the program of visual effects. The PHIGS Validation Tests (PVT) incorporate several innovative design features in order to address these difficulties. The model of deductive inference suggests ways to organize a system as logically complex as the PVT. This complexity makes the use of certain database concepts quite valuable in allowing users to navigate within the system. The problem of inaccessible effects can be addressed by careful design of the user interface, so as to minimize the subjectivity and operational difficulty inherent in testing such features. Subjectivity is minimized by posing short simple questions to the operator, in which the expected answer is randomized. Several design features enhance ease of use, including a customizable interface, self-explanatory displays, and automatic capture of results.Show more Item A constraint-based UIMS using graph unification(Eurographics Association, 1991) Samuel, J. F.Show more This paper describes an experimental UIMS developed to investigate methods of combining and reusing objects within a constraint-based system. A novel approach based on graph-unification facilitated the definition of composite objects and allowed behaviours to be transferred easily from one object to another. A very simple form of local propagation was used as the constraint satisfaction mechanism, which, as well as being fast, could also cope with cyclic dependencies. This method used a time-stamping method which made it possible to express time-dependency in the constraints. The system has features from both class-based and prototype-based object-oriented languages. Dynamic modification of objects can be performed rapidly enough for interactive control. Interfaces built with the system include a variety of 'standard' user interface objects such as sliders as well as a number of physical simulations utilising time-dependent constraints.Show more Item Several approaches to implement the merging step of the split and merge region segmentation(Eurographics Association, 1991) Popovic, M.; Chantemargue, F.; Canals, R.; Bonton, P.Show more The purpose of this paper is to propose several approaches for the implementation of the merging step of split and merge region segmentation. The splitting step has already been studied and its parallelization has subsequently been implemented on a transputer network. First, the most widely known merging step is described. Then, two approaches which are better suited to a parallelization are presented. Next we discuss the principle behind these approaches. Finally region segmentation according to motionbased criteria has been chosen in order to provide results to evaluate the performance of each approach. We emphasize that the description is general and can be applied to all split and merge algorithms. Therefore this work is a contributory factor in the evolution of region segmentation towards its parallelization.Show more Item Integrating Inheritance and Composition in an Objective Presentation Model for Multiple Media(Eurographics Association, 1991) Took, RogerShow more A formal model is presented which combines, in a single structure called a tangle, the power to express both the composition of aggregate objects, and the selective inheritance of object properties over a number of instances or manifestations. The model allows an objective implementation, that is, one in which objects can be created and updated randomly, incrementally, and dynamically. Such a model is ideal as the basis for interactive presentation. The tangle is defined as generic in its node type, and so can model the structure of multiple presentation media.Show more Item Fast Rendering of General Ellipses(Eurographics Association, 1991) Fellner, Dieter W.; Helmberg, ChristophShow more Even though GKS did not include circles and, in a more general form, ellipses and elliptical arcs in the list of elementary graphics primitives, CGM settled this omission with its standardization in 1987. According to CGM as well as to CGI, ellipses and elliptical arcs are defined in a very general way via endpoints of conjugate diameter pairs (CDP). Based on the algorithm of Maxwell & Baker [5] this paper presents a new algorithm for the rendering of general ellipses (i.e. not aligned to the coordinate axes) and elliptical arcs which is not only fast and very well suited for implementation in hardware but also deals with all degenerate cases of ellipses at no extra cost. Furthermore, the algorithm provides all the information which is necessary for the generation of anti-aliased elliptical curves.Show more Item Constructive Page Description Opening Up the Prepress World(Eurographics Association, 1991) Samara, Veronika; Wiedling, Hans-PeterShow more Constructive Page Description (CPD) is an overall approach allowing different kinds of data to be exchanged between a variety of systems and manipulated in arbitrary system environments. Fully changeable pages, which keep information for modification as long as necessary, as well as fully assembled pages, ready for the printing process, can be constructed by the use of CPD. Moreover, descriptions of data as well as operations can be distributed, and so allow the use of networking facilities. CPD is thereby very flexible in handling, combining, and exchanging data and operations used in the construction of pages. In sum, CPD helps bridge the gap between the printing and the computer graphics world; it is an approach to lead prepress towards an open system architecture.Show more Item Serial cuttings matching: An application to muscle fiber characterization(Eurographics Association, 1991) Buche, PatriceShow more In this paper, we present one important aspect of a complete application of numerical image analysis in biology. We want to analyse a biological object through serial cuttings to measure morphological and biochemical parameters. To achieve this, we have to deal with the problem of distortion which appears between the serial cuttings, coming from the biological objects themselves or from the technology used in experimentation process. Our objective is to build a robust routine application. Therefore we have made an effort on the automation degree and the quality of the generated measures. We propose a solution based on a global polynomial transformation model to take into account the distortions and a relaxation process to estimate the model coefficients. The association of these two steps gives a new tool which opens new perspectives to the biologist using even now qualitative or manually obtained quantitative informations to study the biological objects.Show more Item A Symmetrical Input/Output Model(Eurographics Association, 1991) Carlsen, Niels Vejrup; Christensen, Niels JorgenShow more When choosing a graphics system for the run-time support component of a User Interface Management System (UIMS) several problems arise. Existing inputloutput models employed by graphics systems lack support for fine grain design control and for defining links between input and output. Furthermore, hardware maintainability is a problem. We have introduced a new inputloutput model, the symmetrical translation model (STM), which solves these problems through extensibility and symmetry. All input and output techniques are implemented by active objects which are specified using a high level notation. This notation allows the temporal and spatial composition of objects. A UIMS is being constructed at our department based upon this model.Show more Item Geometric Modelling from Range Image Data(Eurographics Association, 1991) Schmitt, Francis; Cken, Xin; Du, Wen-HuiShow more An adaptive surface fitting algorithm is proposed for modelling the digitized surface of a real object described by an array of 3D points sampled on a rectangular mesh and stored in the form of a range image. A G1 -piecewise approximation of the data is obtained by using an adaptive top-down method which combines the Delaunay triangulation technique with a triangular Gregory-Bezier patch model (tGB). The method begins with a rough approximation of the surface and progressively refines it in successive steps in the regions where the accuracy requirement of the approximation is not satisfied. The method, therefore, is essentially a local process. An optimization approach is used to obtain a G '-continuous piecewise approximation where each tGB patch is as smooth and regular as possible. Some experimental results are given to demonstrate the potential usefulness of this approach for the geometric modelling from range image data.Show more Item Animation of Landscapes Using Satellite Imagery(Eurographics Association, 1991) Geymayer, Barbara; Prantl, Manfred; Müller-Seelich, Heimo; Tabatabai, BehnamShow more The paper presents methods to animate synthetic landscapes. The modeling of the landscape, the interactive specification of the flight path and the simulation of an explosion are described. The landscape is visualized by superimposing texture information computed from different satellite data onto a digital elevation model. A pyramid data structure is used to store the texture and digital elevation model data in different resolutions. This approach allows the generation of pictures with constant data density in an efficient way. The flight path is modeled interactively using a wireframe representation of the landscape. An explosion is simulated using physically modeled trajectories of the exploding parts. The approach is explained in the context of the “ERZBERG” animation in which an impressive flight through a valley towards the exploding Erzberg mountain has been generated.Show more Item Interrogation of Offsets of Polynomial Surface Patches(Eurographics Association, 1991) Vafiadou, Maria - Eleni; Patrikalakis, Nicholas M.Show more This paper presents an algorithm for computing the intersection of the offset (or parallel) surface of a polynomial surface patch ( rogenitor) of arbitrary degree, with a straight line. The rogenitor patch is expressed in the tensor product Bernstein form. The intersection problem is reformulated in terms of computing the intersection of two algebraic curves within the parameter s ace of the patch. The tensor product Bernstein form is emplo ed for the representation of these algebraic curves. The solution method is based on subdivision relying on the convex hull roperty of the Bernstein representation of algebraic curves and minimization techniques. The resulting algorithm can form the basis for accurate visualization of offset surfaces through ray tracing methods.Show more Item Tessellation of Curved Surfaces under Highly Varying Transformations(Eurographics Association, 1991) Abi-Ezzi, Salim S.; Shirman, Leon A.Show more We pursue the problem of step size determination for tessellating arbitrary degree polynomial and rational Bezier patches, under highly varying modeling and viewing transformations, to within post-viewing size and/or deviation thresholds specified in display coordinates. The technique involves the computation of derivative bounds of surfaces in modeling coordinates, and the mapping of these bounds into world coordinates (or lighting coordinates), where tessellation takes place by using norms of modeling transformations. A key result of this work is a closed form expression for the maximum scale a perspective transformation is capable of at an arbitrary point in space. This result allows the mapping of thresholds from DC into WC (LC). In practice, while the step size determination needs to take place during every traversal, the costly operations of finding derivative bounds, computing norms of modeling transformations, and factoring viewing transformations take place at creation time.Show more Item Computational Physics : A Modeler - Simulator for animated physical Objects(Eurographics Association, 1991) Luciani, Annie; Jimenez, Stephane; Florens, Jean Loup; Cadoz, Claude; Raoult, OlivierShow more Physical modeling for animation is now firmly established. The present aim is to design and build a structured and well-defined tool rather than merely specific algorithms to simulate physical knowledge. We will first define the basic functions of a modeler - simulator for physical modeling which enables operator gestural control, and where the simulation processes are real time oriented. These constraints cannot be achieved by any kind of models and algorithms. Concerning the theoretical elements, the choice of the underlying Physics and the categorization of interactions will be presented. We will then introduce the Cordis-Anima system, its constructive langage, its real time simulator and its force feedback gestural transducers. Finally, we will describe, with some examples, how we model, simulate and manipulate a large variety of physical objects and scenes with our system.Show more Item Radiosity for Furry Surfaces(Eurographics Association, 1991) Chen, Hong; Wu, En-HuaShow more Though radiosity method is an advanced rendering technique of global illumination, it is still not sufficiently to cope with many natural phenonmena such as furry surfaces. The rendering of furry surfaces has been a long outstanding problem in image synthesis. Therefore, it is of significance to develop an approach to incorporate the rendering of furry surfaces into radiosity method. By combining the concept of texel with the furry radiosity map , established from the radiosity calculation based on the proposed furry form-factor in the paper, a new radiosity algorithm has been developed to produce the images of furry surfaces.Show more Item A Testbed for Image Synthesis(Eurographics Association, 1991) Trumbore, Ben; Lytle, Wayne; Greenberg, Donald P.Show more Image Synthesis research combines new ideas with existing techniques. A collection of software modules that provide such techniques is extremely useful for simplifying the development process. We describe the design and implementation of a new Testbed for Image Synthesis that provides such support. This Testbed differs from previous Testbeds in both its goals and its design decisions. The Testbed design addresses the problems of high model complexity, complicated global illumination algorithms and coarse grain parallel processing environments. The implementation is modular, portable and extensible. It allows for statistical comparison of algorithms and measurement of incremental image improvements, as well as quantitative comparison of Testbed images and light reflectance measured from physical models. The Testbed is designed to interface with any available modeling system. This compatibility was achieved through careful design of the data format that represents environments. The software modules of the Testbed are organized in a hierarchical fashion, simplifying application programming.Show more Item Solid-Interpolating Deformations: Construction and animation of PIPs(Eurographics Association, 1991) Kaul, Anil; Rossignac, JarekShow more Computer programs that simulate the deformations of geometric shapes have played a key role in the increasing popularity of software tools for artistic animation. Previously published techniques for specifying and animating deformations are either limited in their domain or ill suited for interactive editing and visualization. This is because the effects of alterations performed by the animator on the model's parameters may not always be anticipated, and because realtime animation may only be produced by visualizing pre-computed sequences of 3D frames, which are obtained by a slow process and require vast amounts of storage. To support an interactive environment for animation design, we have developed a new, simple, and efficient animation primitive: a Parameterized Interpolating Polyhedron, or PIP for short. PIPs are easily specified and edited by providing their initial and final shapes, which may be any polyhedra, and need not have corresponding boundary elements. PIPs may be efficiently animated on standard graphic hardware because a PIP is a smoothly varying family of polyhedra bounded by faces that evolve with time. The faces have constant orientations and vertices that each move on a straight line between a vertex of the initial shape and a vertex of the final one. The cost of recalculating the time dependant information of a PIP is small in comparison to the display cost. We provide simple and efficient algorithms, based on Minkowski sum operations, for computing PIPs. When both the initial and final shapes are convex, the resulting faces are the true boundary of the deforming object, otherwise subsets of the resulting faces may lie inside the object. In both cases, correct images are automatically generated using standard depth-buffer hardware. The tools we have developed are convenient for interactively designing animation sequences that show the metamorphosis of 3D shapes. They may also be used to simulate the geometric effect of a variety of manufacturing operations, and for interactively selecting the optimal compromise between two or more shapes. They are being integrated in the LAMBADA design and inspection environment for animated assemblies, where deformations and rigid-body motions may be easily combined and synchronized using a hierarchical representation.Show more Item C 2 Gregory patch(Eurographics Association, 1991) Miuraa, Kenjiro Takai; Wangb, Kuo-KingShow more G² continuity of free-form surfaces is sometimes very important in engineering applications. The conditions for G2 continuity between two Bezier patches has been studied and methods developed to ensure such continuity. However, certain restrictions on the shapes of such patches arise within the Bezier-patch formulation. The Gregory patch is a kind of free-form surface patch which is an extension of the Bezier patch such that cross-boundary first derivatives can be specified without restrictions on the compatibility condition. In this paper, we extend the idea of the Gregory patch and develop a formulation for the C² Gregory patch. The properties of the C² Gregory patch are discussed as well as its connection with a Bezier patch and a G² continuous interpolation method based upon such patches.Show more Item Variable-Radius Blending by Using Gregory Patches in Geo- metric Modeling(Eurographics Association, 1991) Harada, T.; Konnoa, K.; Chiyokura, H.Show more Blending surfaces, which connect two curved surfaces smoothly, often appear in geometric modeling. Many of the blending surfaces are variable-radius blends. Variableradius blending surfaces are very important in the design process, but it is difficult to generate such surfaces with existing geometric modelers. This paper proposes a new method to generate variable-radius blends. Instead of the popular rolling-ball method, we adopt “sliding-circle” blending. A circle slides on two curved surfaces so that the circle is perpendicular to a specified control curve, and its trajectory defines a blending surface. A variable-radius blend can be generated if the radius of the circle changes smoothly. In our method, the shape of the variable-radius blend is represented by Gregory patches. The Gregory patch is an extension of a Bezier patch and two Gregory patches can be connected together with tangential continuity. The characteristics of the Gregory patch are suitable for representing blending surfaces with geometric modelers.Show more Item Time Complexity of Monte Carlo Radiosity(Eurographics Association, 1991) Shirley, PeterShow more The time complexity of Monte Carlo radiosity is discussed, and a proof is given that the expected number of rays required to produce a satisfactory radiosity solution for N zones is O(N). A satisfactory solution is defined to be one in which the variance of radiance estimates for each zone is below a predefined threshold. The proof assumes that the radiance is bounded, and the area ratio of the largest to smallest zone is bounded.Show more