Volume 15 (1996)

Permanent URI for this community

https://diglib.eg.org/handle/10.2312/71

Browse

Now showing 1 - 20 of 65

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.
The Layout Design Language: A Technique for Generating Layout Plans
(Blackwell Science Ltd and the Eurographics Association, 1996) Grimsdale, R.L.; Chang, C.W.
The work described in this paper arose from a requirement for a system to support the production of models for training simulator visual systems and other visualisation applications. To reduce the labour involved in generating such models, it was decided to develop a technique whereby models could be generated by a high-leuel language. For these models there is a requirement to generate 2-D plans showing, for example, the locations of roads and buildings, subsequently 3-D models of the buildings are placed at the defined locations. The 2-D plans can be created through the use of the Layout Design Language (LD-Language). LD-Language has been formulated particularly for designing urban area street plans.The primitive elements of the LD-Language, plots, are assembled into patterns which can be further combined into a layout plan, with some support provided by the system. The work reported has successfully demonstrated that a complex layout plan can be developed using this language.
Functions Defining Arbitrary Meshes - A Flexible Interface between Numerical Data and Visualization Routines
(Blackwell Science Ltd and the Eurographics Association, 1996) Rumpf, Martin; Schmidt, Alfred; Siebert, Kunibert G.
Most of the rendering tools in scientific visualization are restricted to special data structures which differ substantially from the data formats used in numerical applications. Trying to close this gap, we present an interface between data from numerical methods on general types of grids - like cuboidal, prismatic, simplicial, parametric, mixed, or hierarchical meshes - and general visualization routines. It is based on a procedural approach managing a collection of arbitrary elements and a set of functions describing each element type. No mapping of (an in general enormous amount of) numerical data onto new data structures is necessary- a user may use his own data structures and only has to provide this small set of procedures and functions. The visualization tools will then use these routines to access (temporarily and locally) data of interest, like information about a single element. Compared with display routines on a specialized data structure, this general interface does not produce much cpu overhead.
Implicit Sweep Objects
(Blackwell Science Ltd and the Eurographics Association, 1996) Crespin, Benoit; Blanc, Carole; Schlick, Christophe
SCROOGE:Perceptually-Driven Polygon Reduction
(Blackwell Science Ltd and the Eurographics Association, 1996) Reddy, M.
Many real-time 3D graphics renderers represent each object as a collection of simple polygons. The complexity of this polygon structure is of practical relevance because it can manifestly affect the performance of the graphics system. It is therefore common place to find techniques to reduce the polygonal complexity of a model with the ultimate aim of improving the interactivity of the application. In the past, many of these schemes have not been concerned with the perceptual side-effects of this reduction and as a result a number of visual incongruities are often perceivable when these correspondingly-reduced representations are employed. As an attempt to circumvent these problems, this paper presents a methodology for reducing the polygonal complexity of a model, whilst retaining a degree of perceptual predictability. This allows the visual consequences of the degradation to be quantified and accurately modelled.
Surface Reconstruction from Unstructured 3D Data
(Blackwell Science Ltd and the Eurographics Association, 1996) Algorri, Maria-Elena; Schmitt, Francis
Building 3 0 models from unstructured data is a problem that arises increasingly as new 30 scanning technology is able to produce large and complex databases of full 3 0 information. Huge efforts put into segmenting entire sets of 20 images demand robust tools that are then able to reconstruct any arbitrary 30 surface segmented from the images. In this paper we propose an algorithmic methodology that automatically produces a surface from a set of points in ?3 about which we have no topological knowledge. Our method uses a spatial decomposition and a surface tracking algorithm to produce a rough approximation S of the unknown manifold S. The produced surface S serves as a robust initialisation for a physically based modeling technique that yields the fine details of S and so improves the quality of the reconstruction.
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.
Scripting Interactive Physically-Based Motions with Relative Paths and Synchronization
(Blackwell Science Ltd and the Eurographics Association, 1996) Lamouret, Alexis; Gascuel, Marie-Paule
This paper presents a novel approach for facilitating the use of physically based models by animators. The idea is to let the user guide motion at a high level of control by giving approximate desired trajectories and synchronization constraints between the objects over time, while a simulation module computes the final motion, dealing with collision detection and response, and enhancing realism.The objects, which are either isolated or components of an articulated structure, are guided through the specification of key-positions and orientations, defined by coordinates that can be fixed or relative to another object. The animation sequence is scripted by specifying a graph of synchronization constraints between objects over time. During the animation, objects automatically regulate their speed in order to meet these constraints.
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).
The Production of Volume Data from Triangular Meshes Using Voxelisation
(Blackwell Science Ltd and the Eurographics Association, 1996) Jones, Mark W.
Voxelisation is the term given to the process of converting data from one source type into a three dimensional volume of data values. The techniques known collectively as volume visualisation can then be applied to the data in order to produce a graphical representation of the object. This paper gives a practical approach to the voxelisation of data in the form of triangular meshes, and demonstrates the use of the method on various datasets. Visualisation is achieved by a method also described in the paper.
Dynamics and Chaos: The Spherical Pendulum
(Blackwell Science Ltd and the Eurographics Association, 1996) Palacios, Antonio; Gross, Lee M.; Rockwood, Alyn P.
All but the simplest of dynamical systems contain nonlinearities that play an important role in modeling and simulating physical systems. They create unpredictable (chaotic) behavior that is often hidden or neglected in traditional solutions. A simple dynamical system, the spherical pendulum, is introduced to illustrate issues, principles, and effects of chaos in dynamics. The spherical pendulum is a two degrees of freedom nonlinear system with a pivot point in space. The equations of motion for the pendulum are derived, simulated, and animated. A periodical perturbation is applied to the pivot point producing radically different behavior.
Accelerated Evaluation of Box Splines via a Parallel Inverse FFT
(Blackwell Science Ltd and the Eurographics Association, 1996) McCool, Michael D.
Box splines are a multivariate extension of uniform univariate B-splines. Direct evaluation of a box spline basis function can he difficult but they have a relatively simple Fourier transform and can therefore be evaluated with an inverse FFT. Symmetry recursive evaluation of the coefficients, and parallelization can be used to improve absolute performance. A windowing function can also he used to reduce truncation artifacts. We explore all these options in the context of a high-performance parallel implementation. Our goal is the provision of an empirical touchstone for the inverse FFT evaluation of box spline basis functions, for eventual application to forward projection (splat-based) volume rendering.
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.

Browse

Browsing Volume 15 (1996) by Issue Date

Results Per Page

Sort Options