EG1991 Proceedings (Technical Papers)

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(Eurographics Association, 1991) -
Computational Physics : A Modeler - Simulator for animated physical Objects
(Eurographics Association, 1991) Luciani, Annie; Jimenez, Stephane; Florens, Jean Loup; Cadoz, Claude; Raoult, Olivier
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.
Radiosity for Furry Surfaces
(Eurographics Association, 1991) Chen, Hong; Wu, En-Hua
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.
Construction Techniques of Graphic, Direct-Manipulation User Interfaces
(Eurographics Association, 1991) Preea, Wolfgang; Pornberger, Gustav; Sikora, Hermann
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.
Time Complexity of Monte Carlo Radiosity
(Eurographics Association, 1991) Shirley, Peter
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.
Liberation from Flatland: 3D Interaction Based on the Desktop Bat
(Eurographics Association, 1991) Slater, Mel; Davison, Allan
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.
Geometric Modelling from Range Image Data
(Eurographics Association, 1991) Schmitt, Francis; Cken, Xin; Du, Wen-Hui
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.
Low Sampling Densities using a psychovisual approach
(Eurographics Association, 1991) Bouville, Christian; Tellier, Pierre; Bouatouch, Kadi
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.
Animation of Landscapes Using Satellite Imagery
(Eurographics Association, 1991) Geymayer, Barbara; Prantl, Manfred; Müller-Seelich, Heimo; Tabatabai, Behnam
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.
Interrogation of Offsets of Polynomial Surface Patches
(Eurographics Association, 1991) Vafiadou, Maria - Eleni; Patrikalakis, Nicholas M.
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.
Using temporal and spatial coherence for accelerating the calculation of animation sequences
(Eurographics Association, 1991) Gröller, Eduard; Purgathofer, Werner
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.
Sampling and Anti-Aliasing of Discrete 3-D Volume Density Textures
(Eurographics Association, 1991) Sakas, Georgios; Gerth, Matthias
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.
Combining Volume Rendering with Line and Surface Rendering
(Eurographics Association, 1991) Frühauf, Martin
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.
MOVE-X: A System for Combining Video Films and Computer Animation
(Eurographics Association, 1991) Ertl, Gerhard; Müller-Seelich, Heimo; Tabatabai, Behnam
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.
Shading with Area Light Sources
(Eurographics Association, 1991) Tanaka, Toshimitsu; Takahashi, Tokiichiro
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.
Continuation Methods for Approximating Isovalued Complex Surfaces
(Eurographics Association, 1991) Zahlten, Cornelia; Jürgens, Hartmut
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.
A Testbed for Image Synthesis
(Eurographics Association, 1991) Trumbore, Ben; Lytle, Wayne; Greenberg, Donald P.
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.
Declarative Graphics And Dynamic Interaction
(Eurographics Association, 1991) Johnson, C.W.; Harrison, M.D.
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.
FACES: Facial Animation, Construction and Editing System
(Eurographics Association, 1991) Patel, Manjula; Willis, Philip J.
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.
Timewarps: A Temporal Reparameterization Paradigm for Parametric Animation
(Eurographics Association, 1991) Smith, Jeff; Drewery, Karin
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.

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