Issue 3

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https://diglib.eg.org/handle/10.2312/74

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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.
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.
Output-SensitiveVisibility Algorithms for Dynamic Scenes with Applications to Virtual Reality
(Blackwell Science Ltd and the Eurographics Association, 1996) Sudarsky, Oded; Gotsman, Craig
An output-sensitive visibility algorithm is one whose runtime is proportional to the number of visible graphic primitives in a scene model-not to the total number of primitives, which can be much greater. The known practical output-sensitive visibility algorithms are suitable only for static scenes, because they include a heavy preprocessing stage that constructs a spatial data structure which relies on the model objects positions. Any changes to the scene geometry might cause significant modifications to this data structure. We show how these algorithms may be adapted to dynamic scenes. Two main ideas are used: first, update the spatial data structure to reflect the dynamic objects current positions- make this update efficient by restricting it to a small part of the data structure. Second, use temporal bounding volumes (TBVs) to avoid having to consider every dynamic object in each frame. The combination of these techniques yields efficient, output-sensitive visibility algorithms for scenes with multiple dynamic objects. The performance of our methods is shown to be significantly better than previous output-sensitive algorithms, intended for static scenes.TBVs can be adapted to applications where no prior knowledge of the objects trajectories is available, such as virtual reality (VR), simulations etc. Furthermore, they save updates of the scene model itself- notjust of the auxiliary data structure used by the visibility algorithm. They can therefore be used to greatly reduce the communications overhead in client-server VR systems, as well as in general distributed virtual environments.
Implicit Sweep Objects
(Blackwell Science Ltd and the Eurographics Association, 1996) Crespin, Benoit; Blanc, Carole; Schlick, Christophe
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.
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).
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.
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.
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.
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.
Special Effects with Half-Toning
(Blackwell Science Ltd and the Eurographics Association, 1996) Buchanan, John W.
Half-toning is the process by which gray-scale images are approximated with sets of black and white pixels. The process works because our eyes perceive a local average, thus half-toning seeks to approximate the local average. Ideally this approximation should be accomplished without introducing undesirable artifacts.In many situations the stylized display of images is desired. Often this stylized display is accomplished by the addition of semi-structured artifacts. In current applications the designer processes the image using tools provided by some image processing package. The resulting image is then half-toned and printed. Half-toning these processed images can reduce the visual impact of the special effects that have been introduced in the image.In this paper we show that the processes of controlled artifact introduction and half-toning can successfully be combined. By combining these two processes we ensure that the printed image is what the designer intended. We present a brief overview of the current error-diffusion half-toning techniques. We then propose several ways in which artifacts can be introduced to the image. This discussion is accompanied by a set of illustrative images.In particular, we discuss the introduction of false edges and the alteration of the scan pattern. We illustrate these techniques with a variety of images.We conclude the paper with a discussion on these new half-toning methods for the generation of binary gray-scale textures. In addition to showing how to generate these binary gray-scale textures we also show how these gray-scale textures can be used to half-tone images.
Demand-Driven Geometry Transmission for Distributed Virtual Environments
(Blackwell Science Ltd and the Eurographics Association, 1996) Schmalstieg, Dieter; Gervautz, Michael
We present a strategy for rendering in distributed virtual environments. A geometry database is maintained by a server, while users invoke individual clients to interact with the environment. Instead of downloading a complete copy of the geometry data, the data is distributed on demand, thus gaining signifcant savings in network bandwidth. Our strategy combines several techniques, including levels of detail, progressive refinement and graceful degradation to deliver the data"just in time" over the network to the rendering process. The method allows operate on a tight resource budget, which important if attempting to use low cost systems for virtual reality applications.
A Platform for User-Tailored Interaction Development in 2D, 3D, and VR
(Blackwell Science Ltd and the Eurographics Association, 1996) Encarnacao, L. Miguel; Fechter, Jurgen; Grunert, Thomas; Strasser, Wolfgang
The discussion on the advantages and disadvantages of 2D, 3D, and VR interfaces and their applicability to different types of systems, users, and information led to a series of stand-alone implementations that lack the possibility of realizing an integrated approach. The acceptance of the different interaction techniques will depend on their success in practical applications, i.e. with systems that are used by different users for different purposes. Since this acceptance is especially hard to achieve in computer-critical environments, such as medicine, we developed a software environment that allows for the development, integration, and user-centered evaluation of existing and new interaction techniques for their use in medical applications. This environment is equipped with an innovative message-passing functionality that provides the communication to and among application objects in 2D, 3D, and VR. Furthermore, the environment contains a component for user-adapted interaction and system support at runtime.
A Three Dimensional Image Cache for Virtual Reality
(Blackwell Science Ltd and the Eurographics Association, 1996) Schaufler, Gernot; Sturzlinger, Wolfgang
Despite recent advances in rendering hardware, large and complex virtual environments cannot be displayed with a sufficiently highframe rate, because of limitations in the available rendering performance.This paper presents a new approach of software accelerated rendering which draws from the concepts of impostors, hierarchical scene subdivision and levels of detail. So far software optimization in real-time rendering has merely considered individual objects. This work is actually optimizing the rendering of the whole virtual environment by implementing a three dimensional image cache. It speeds up rendering for large portions of the scene by exploiting the coherence inherent in any smooth frame sequence.The implementation of the three dimensional image cache is discussed and the savings in rendering load achievable on a suitable hardware platform are presented.
Reusable Radiosity Objects
(Blackwell Science Ltd and the Eurographics Association, 1996) Ouhyoung, Ming; Chuang, Yung-Yu; Liang, Rung-Huei
Because of the view independence and photo realistic image generation in a diffuse environment, radiosity is suitable for an interactive walk through system. The drawback of radiosity is that it is time-consuming in form factor estimation, and furthermore, inserting, deleting or moving an object makes the whole costly rendering process repeat itself. To solve this problem, we encapsulate necessary information for form factor calculation and visibility estimation in each object, which is called a reusable radiosity object. An object is defined as a cluster or clusters of triangles. Whenever a scene updates, the radiosity algorithm looks up the prestored information in each object, thus speeding itself up by two orders of magnitude. Besides, solution time based on cluster representatives is linear to the number of objects since each object is reusable, encapsulated with preprocessed data in every level of hierarchy. We also analyze the unregarded error on visibility estimation and propose a statistically optimal adaptive algorithm to maintain the same error for each link.
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.
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.
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.
Head-Tracked Stereo Viewing with Two-Handed 3 D Interaction for Animated Character Construction
(Blackwell Science Ltd and the Eurographics Association, 1996) Turner, Russell; Gobbetti, Enrico; Soboroff, Ian
In this paper, we demonstrate how a new interactive 3 D desktop metaphor based on two-handed 3 D direct manipulation registered with head-tracked stereo viewing can be applied to the task of constructing animated characters. In our configuration, a six degree-of-freedom head-tracker and CrystalEyes shutter glasses are used to produce stereo images that dynamically follow the user head motion. 3 D virtual objects can be made to appear at a fixed location in physical space which the user may view from different angles by moving his head. To construct 3 D animated characters, the user interacts with the simulated environment using both hands simultaneously: the left hand, controlling a Spaceball, is used for 3 D navigation and object movement, while the right hand, holding a 3 D mouse, is used to manipulate through a virtual tool metaphor the objects appearing in front of the screen. In this way, both incremental and absolute interactive input techniques are provided by the system. Hand-eye coordination is made possible by registering virtual space exactly to physical space, allowing a variety of complex 3 D tasks necessary for constructing 3 D animated characters to be performed more easily and more rapidly than is possible using traditional interactive techniques. The system has been tested using both Polhemus Fastrak and Logitech ultrasonic input devices for tracking the head and 3 D mouse.

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