EG 1996 Conference Proceedings

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https://diglib.eg.org/handle/10.2312/13895

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Intelligent Control for Haptic Displays
(Blackwell Science Ltd and the Eurographics Association, 1996) Munch, Stefan; Stangenberg, Martin
Usually, a mouse is used for input activities only, whereas output from the computer is sent via the monitor and one or two loudspeakers. But why not use the mouse for output, too? For instance, if it would be possible to predict the next interaction object the user wants to click on, a mouse with a mechanical brake could stop the cursor movement at the desired position. This kind of aid is especially attractive for small targets like resize handles of windows or small buttons.In this paper, we present an approach for the integration of haptic feedback in everyday graphical user interfaces. We use a specialized mouse which, is able to apply simple haptic information, to the user s hand and index finger. A multi-agent system has been designed which observes the user in order to predict the next interaction object and launch haptic feedback, thus supporting positioning actions with the mouse. Although primarily designed in order to provide intelligent haptic feedback, the system can be combined with other output modalities as well, due to its modular and flexible architecture.
Radiosity for dynamic scenes in flatland with the visibility complex
(Blackwell Science Ltd and the Eurographics Association, 1996) ORTI, Rachel; RIVIERE, Stephane; DURAND, Fredo; PUECH, Claude
The radiosity method is particularly suitable for global illumination calculations in static environments. Nonetheless, recent applications of image synthesis such as architectural simulation or lighting design require the ability to modify environments. Previous methods have attempted to deal with dynamic environments (environments where the geometry, the material properties, etc., can change)but still suffer some limitations in the case of moving objects. One of the main problems remaining is the efficient and accurate detection of which form factors must really be recomputed, since their calculation is the most time-consuming part of the radiosity method. To correctly understand and solve this problem, we start with a method in 2D for polygonal scenes using the visibility complex. It is a powerful data structure representing the visibility relationships between objects in the plane. We have developed and implemented an algorithm which uses this structure to efficiently compute the discontinuity mesh and the form factors for static scenes. We also propose an extension to our algorithm to efficiently update only the modified form factors when an object is moving. This approach enhances our understanding and will hopefully lead to efficient solutions in 3D.
An Energy-Based Approach for Contact Force Computation
(Blackwell Science Ltd and the Eurographics Association, 1996) Faure, Francois
A new approach for computing resting contact forces between solids is presented, which handles both static and sliding friction, while avoiding the problems arising from previous approaches. Each iteration provides values for all unknowns and needs a constant computation time. The first iteration is a global dynamic solution involving inertia and external forces. The subsequent iterations consist of global redistributions of energy through the solids in order to restrict the values within correct bounds, leading to a progressive refinement of the solution. This allows the termination of the computation when a user-defined level of precision is reached. Convergence is proven in the frictionless case.The method is concise and is easily usable in a motion control system. It was implemented and tested on some examples involving simultaneously static and sliding friction along with motion control.
Interpolatory Subdivision on Open Quadrilateral Nets with Arbitrary Topology
(Blackwell Science Ltd and the Eurographics Association, 1996) Kobbelt, Leif
A simple interpolatory subdivision scheme for quadrilateral nets with arbitrary topology is presented which generates C1 surfaces in the limit. The scheme satisfies important requirements for practical applications in computer graphics and engineering. These requirements include the necessity to generate smooth surfaces with local creases and cusps. The scheme can be applied to open nets in which case it generates boundary curves that allow a C0-join of several subdivision patches. Due to the local support of the scheme, adaptive refinement strategies can be applied. We present a simple device to preserve the consistency of such adaptively refined nets.
Full-range approximation of triangulated polyhedra.
(Blackwell Science Ltd and the Eurographics Association, 1996) Ronfard, Remi; Rossignac, Jarek
We propose a new algorithm for automatically computing approximations of a given polyhedral object at different levels of details. The application for this algorithm is the display of very complex scenes. where many objects are seen with a range of varying levels of detail. Our approach is similar to the region-merging method used for image segmentation. We iteratively collapse edges, based on a measure of the geometric deviation from the initial shape. When edges are merged in the right order, this strategy produces a continuum of valid approximations of the original object, which can be used for faster rendering at vastly different scales.
Generation of Smooth Surfaces by Controlling Curvature Variation
(Blackwell Science Ltd and the Eurographics Association, 1996) Higashi, Masatake; Tsutamori, Hideo; Hosaka, Mamoru
To satisfy a designer s intention for constructing aesthetic shapes such as automotive bodies, we propose a surface generation method. In the surface design process, designers determine shapes according to their great concern for the reflected images of vehicle surroundings, shade lines and highlight lines. Since reflection and shading are affected by changes of surface normal, the curvature variation of the surface, which represents the change of the surface normal, should be smooth and distributed as designers want. The proposed method controls curvature distribution directly by determining a surface shape from an evolute, which is a locus of the curvature center of the generatrix and moves along directrices to form the surface. It first generates evolutes of boundary curves to be generatrices as rational Bezier curves, then interpolates their shapes with the Bezier polygons, and locates the interpolated shape to the corresponding position of the directrices. By applying this method, we have confirmed that a smooth shape is generated from four boundary curves.
Fractal modeling using free form techniques
(Blackwell Science Ltd and the Eurographics Association, 1996) Zair, Chems Eddine; Tosan, Eric
IFS models have become a powerful tool for the construction of fractal sets. They offer a straightforward way to generate complex, self-similar figures as attractors. However, they present the fundamental disadvantage of providing little control over the global form of the attractor. In contrast, free form techniques give a high control over smooth man-made objects with the use of a set of control points.In this paper, we present a new approach of fractal modeling which is based on IFS theory. We shall use free form techniques to give a practical and efficient way to build controlled fractal attractors. The resulting effect consists on the ability to deform a fractal shape interactively into the desired shape, in the same way as parametric forms (Bezier, splines).
3D Interactive Topological Modeling using Visible Human Dataset
(Blackwell Science Ltd and the Eurographics Association, 1996) Beylot, P; Gingins, P; Kalra, P; Thalmann, N Magnenat; Maurel, W; Thalmann, D; Fasel, J
Availability of Visible Human Dataset (VHD)has provided numerous possibilities for its exploitation in both medical applications and 3D animation. In this paper, we present our interactive tools which enable extraction of surfaces for different organs, including bones, muscles, fascia, and skin, from the VHD. The reconstructed surfaces then are used for defining the inter-relationship of organs, a process we refer to as topological modeling. A data base is constructed, which encapsulates structural, topological, mechanical and other relevant information about organs. A 3D interactive tool enables the building and editing of this data base. Such a data base can later be used for different applications in fields such as medicine, sports, education, and entertainment.
CCD-Camera Based Optical Beacon Tracking for Virtual and Augmented Reality
(Blackwell Science Ltd and the Eurographics Association, 1996) Madritsch, Franz; Gervautz, Michael
We introduce a scheme for optical beacon tracking using two CCD-cameras and LED beacons. Due to the sub-pixel accuracy of the beacon detection algorithm a very high precision can be achieved so that the tracking method is suitable for augmented reality applications. We describe the assembly of the equipment needed for the whole tracking system, the behavior of LED-beacons, and how three beacons can be combined to form a 6-DOF tracker. A report on our accuracy evaluation and its results are given. Furthermore we describe two application prototypes in which the tracker was incorporated and tested.
Computation of Higher Order Illumination with a Non-Deterministic Approach
(Blackwell Science Ltd and the Eurographics Association, 1996) Bouatouch, Kadi; Pattanaik, S. N.; Zeghers, Eric
In spite of the number of efforts made by the computer graphics researchers, till today the computation of view-independent global illumination in an environment containing non-diffusely reflecting objects is a non-resolved problem. In general, non-deterministic techniques seem to be capable of solving this problem. In this article we propose one such non-deterministic method which will permit such calculation by using a combined technique of higher order function approximation and particle tracing. We have used multi-wavelets as basis functions and have calculated the illumination function approximation coefficients by exploiting the adjointness between the radiance equation and the potential equation.
Surface Graph Sketching
(Blackwell Science Ltd and the Eurographics Association, 1996) Hutchinson, D.; Lin, F.; Hewitt, W.T.
The production of patterns and designs upon surfaces has received only limited attention, with texturing techniques being accepted as adequate. Texturing, however, can be a very unsatisfactory and clumsy method of producing complex and accurate designs upon a surface, even more so with surfaces such as NURBS where a texture may appear very much distorted when mapped to a surface. This paper introduces a new approach called surface graph sketching which draws upon ideas from planar graph sketching for the construction of complex curve networks across parametrically defined surfaces. Surface curves can be created by a number of methods and stored in the parameter space of the surface thereby allowing intricate and more importantly accurate surface designs to be created. Regions of the surface may be assigned a property such as colour or texture, or cut away to produce holes. Surface graph sketching has a number of applications, in the design of trimming curves, surface patterning and texture map definitions.
Incremental constraint modelling in a feature modelling system
(Blackwell Science Ltd and the Eurographics Association, 1996) Laakko, Timo; Mantyla, Martti
The techniques of constraint propagation have recently been successfully applied to feature-based design. Because of their speed, constraint propagation methods allow incremental design and rapid local modifcations of the part. However, cyclic constraints cause serious problems to current constraint propagation algorithms. Variational geometric design systems can, in principle, manage these cases. Unfortunately, this typically requires complete re-evaluation of the underlying set of constraint equations, making the method unsuitable for interactive use.The proposed system aims to localize the problem of constraint solving and maintenance. The constraint graph of the part or assembly is divided into several independent partial graphs, subsystems. Afterwards, each subsystem is handled separately using a selected constraint solving technique for the subsystem.
Automatic Generation of Multiresolution Boundary Representations
(Blackwell Science Ltd and the Eurographics Association, 1996) Andujar, C.; Ayala, D.; Brunet, P.; Arinyo, R. Joan; Sole, J.
The paper focuses on automatic simplification algorithms for the generation of a multiresolution family of solid models from an initial boundary representation of a polyhedral solid. An algorithm for general polyhedra based on an intermediate octree representation is proposed. Simplified elements of the multiresolution family approximate the initial solid within increasing tolerances. A discussion among different octree-based simplification methods and the standard marching cubes algorithm is presented.
Compositing Computer and Video Image Sequences: Robust Algorithms for the Reconstruction of the Camera Parameters
(Blackwell Science Ltd and the Eurographics Association, 1996) Berger, M.-O.; Chevrier, C.; Simon, G.
Augmented reality shows great promises in fields where a simulation in situ would be impossible or too expensive. When mixing synthetic and real objects in the same animated sequence, we must be sure that the geometrical coherence as well as the photometrical coherence is ensured. One major challenge is to compute the camera viewpoint with sufficient accuracy to ensure a satisfactory composition. We especially address this point in this paper using computer vision techniques and robust statistical methods. We prove that such techniques make it possible to compute almost automatically the viewpoint for long video sequences even for bad quality images in outdoor environments. Significant results on the lighting simulation of the bridges of Paris are shown.
Method for Calculation of Sky Light Luminance Aiming at an Interactive Architectural Design
(Blackwell Science Ltd and the Eurographics Association, 1996) Dobashi, Yoshinori; Kaneda, Kazufumi; Yamashita, Hideo; Nishita, Tomoyuki
Recently, computer graphics are frequently used for both architectural design and visual environmental assessment. Using computer graphics, designers can easily compare the effect of the natural light on their architectural designs under various conditions, such as different times of day, seasons, atmospheric conditions (clear or overcast sky) or building wall materials. In traditional methods of calculating the luminance due to sky light, however, all calculation must be performed from scratch if such conditions undergo change. Therefore, to compare the architectural designs under different conditions, a great deal of time has to be spent on generating the images.This paper proposes a new method of quickly generating images of an outdoor scene, taking into account glossy specular reflection, even if such conditions change. In this method, luminance due to sky light is expressed by a series of basis functions, and basis luminances corresponding to each basis function are precalculated and stored in a compressed form in the preprocess. Once the basis luminances are calculated, the luminance due to sky light can be quickly calculated by the weighted sum of the basis luminances. Several examples of an architectural design demonstrate the usefulness of the proposed method.
BOXTREE: A Hierarchical Representation for Surfaces in 3D
(Blackwell Science Ltd and the Eurographics Association, 1996) Barequet, Gill; Chazelle, Bernard; Guibas, Leonidas J.; Mitchell, Joseph S.B.; Tal, Ayellet
We introduce the boxtree, a versatile data structure for representing triangulated or meshed surfaces in 3D. A boxtree is a hierarchical structure of nested boxes that supports efficient ray tracing and collision detection. It is simple and robust, and requires minimal space. In situations where storage is at a premium, boxtrees are effective alternatives to octrees and BSP trees. They are also more flexible and efficient than R-trees, and nearly as simple to implement.
Extraction of Typographic Elements from Outline Representations of Fonts
(Blackwell Science Ltd and the Eurographics Association, 1996) Shainir, Ariel; Rappoport, Ari
Digital typefaces for computer graphics and multimedia applications should be capable of supporting operations such as font variations, transformations. deformations and blending. A powerful implementation of such operations must rely on the inherent typographic attributes of the typeface. However, even today s most advanced typeface representations support only geometric outline representations and basic font variations.In this paper we discuss high-level typeface representations which we term Parametric Typographic Representations (PTRs). We present an algorithm for automatically extracting typographic elements of typefaces from their outline representation, which, is an essential initial step in converting typefaces from outline representations to PTRs. The extracted typographic elements include serifs, bars. sterns, slants, bows, arcs, curve stems and curve bars. Most notable is the treatment of serifs, which are represented by finite-automata. The algorithm only needs to learn a serif type once, and is then capable of automatically recognizing it in different typefaces.We show an application of a PTR for automatic high-quality hinting of fonts, which is one of the most important stages in, digital font production. Our system was used to generate hints for dozens of thousands of Kanji, Roman and Hebrew characters.
Vector Field Based Texture Mapping of Animated Implicit Objects
(Blackwell Science Ltd and the Eurographics Association, 1996) Smets-Solanes, Jean-Paul
This paper shows that an adequate use of vectorfields can solve most inconsistencies related to texture mapping that appear in current animation and rendering systems based on implicit objects. The method used is based on the concept of a virtual skin. A skin with its own texture mapping is spread over an implicit object and is constrained to stick to the deformation of the implicit object. A vectorfield is used to compute the relationship between the motion of the skin and the deformation of the object. Visual and implementation issues are discussed with respect to typical applications of implicit objects in computer graphics.
Simplification of Global-Illumination Meshes
(Blackwell Science Ltd and the Eurographics Association, 1996) Hughes, Merlin; Lastra, Anselmo A.; Saxe, Edward
We present a methodfor simplifying the meshes produced as solutions to global illumination problems, reducing geometric complexity while retaining the perceived imagefidelity. The method has been applied to produce meshes of linearly, quadratically and cubically colour-interpolated triangles. The goal of our work is to permit interactive rendering of more complex global illumination solutions through the application of simplification algorithms as well as the use of more powerful rendering primitives.
Three-Dimensional Modeling and Effects on Still Images
(Blackwell Science Ltd and the Eurographics Association, 1996) Zakait, Yaron; Rappoport, Ari
Designers and creative artists use computer graphics and image processing effects on stall photographs in application areas such as advertising entertainment broadcasting and the arts Most of the effects available in research arid commercial work are two-dimensional in nature, for example image processing filters [blur, edge enhancement) and creative effects (tilings, reflections) There is almost no usage of information taken from the 3-D world in which the objects appearing an the image are located.In this paper we present a novel method for creating 3-D effects on photographs or in general on any image created by rendering a 3-D world The artist interacts with the image using a set of intuitive direct manipulation interface objects These objects let the user define a 3-D model, display at, and manipulate it in a 3-D space which is correlated with that of the input image.The generated model can be an arbitrarily complex 3-D polyhedron Any texture, including texture taken from the input photograph, can be mapped into any of its faces arid used for special effects We discuss and show examples for effects such as copy and paste, motion blur, model editing and deformations lighting effects, and shadows.

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