Volume 15 (1996)

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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.
3D Reconstruction of Complex Polyhedral Shapes from Contours using a Simplified Generalized Voronoi Diagram
(Blackwell Science Ltd and the Eurographics Association, 1996) Oliva, J-M.; Perrin, M.; Coquillart, S.
We are interested in modelling the suface of very irregular objects known through a few planar polygonal cross-sections. This problem is considered difficult when severe topology and morphology variations appear between neighbouring cross-sections (multi-branching, holes, disconnected areas). Only few methods deal with this problem in a systematic way.The paper describes an original method allowing to build, in a fully automatic and systematic way, an external surface with a valid topology in any case. It moreover allows to adjust details of the reconstructed surface in view of the morphologies and topologies of the various initial cross-sectional contours.At first, a global correspondence is operated between each couple of adjacent cross-sections by extracting polygonal areas of difference. Next steps are based on the computation in each area of difference of the bisector network, a well-defined simplified generalised Voronoi diagram. This structure is used both for connecting initial contour points and for interpolating new intermediate portions of contours. It depends on the complexity of initial 2D shapes. Interpolation stage is then recursively operated until a satisfactory surface has been obtained or until a maximum number of new intermediate cross-sectional contours have been built. The valid final suface is directly obtained by concatenating all the tiling areas of difference without need of any post processing step. The processing of several real data related to geological bodies or human organs has proved that the described method allows detailed modelling of irregular objects with very performing CPU times. The reconstruction appears insensitive to severe variations of the object shape, including apparitions of holes or disconnections.
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.
Adaptive Enumeration of Implicit Surfaces with Affine Arithmetic
(Blackwell Science Ltd and the Eurographics Association, 1996) de Figueiredo, Luiz Henrique; Stolfi, Jorge
We discuss adaptive enumeration and rendering methods for implicit surfaces, using octrees computed with affine arithmetic, a new tool for range analysis. Affine arithmetic is similar to standard interval arithmetic, but takes into account correlations between operands and sub-formulas, generally providing much tighter bounds for the computed quantities. The resulting octrees are accordingly much smaller, and the rendering faster.
Adaptive Sampling of Implicit Surfaces for Interactive Modelling and Animation
(Blackwell Science Ltd and the Eurographics Association, 1996) Desbrun, Mathieu; Tsingos, Nicolas; Gascuel, Marie-Paule
This paper presents a new adaptive sampling method for implicit surfaces that can be used in both interactive modelling and animation. The algorithm samples implicit objects composed of blending primitives and efficiently maintains this sampling over time, even when their topology changes (during fractures and fusions). It provides two complementary modes of immediate visualization: displaying"scales" lying on the surface, or a"primitive-wise" polygonization. The sampling method efficiently avoids unwanted blending between different parts of an object. Moreover, it can be used for partitioning an implicit surface into local bounding boxes that will accelerate collision detection during animation and ray-intersections during final rendering.
Animation of Human Diving
(Blackwell Science Ltd and the Eurographics Association, 1996) Wooten, Wayne L.; Hodgins, Jessica K.
The motion of a human platform diver was simulated using a dynamic model and a control system. The dynamic model has 32 actuated degrees of freedom and dynamic parameters within the range of those reported in the literature for humans. The control system uses algorithms for balance, jumping, and twisting to initiate the dive, sequences of desired values for proportional-derivative servos to perform the aerial portion of the dice, and a state machine to sequence the actions throughout the dice. The motion of the simulated diver closely resembles video footage of dices performed by human athletes. The control and simulation techniques presented in this paper are useful for providing realistic motion for synthetic actors in computer animations and virtual environments and may some day be useful for analysis of sports performance.
Approximate Conversion of Parametric to Implicit Surfaces
(Blackwell Science Ltd and the Eurographics Association, 1996) Velho, Luiz; Gomes, Jonas
In this paper we present a framework for the approximate conversion of parametric to implicit surfaces. It takes as input a parametric description and generates a piecewise analytic implicit representation. The conversion process consists of three steps: 1) the parametric surface is rasterized into a volumetric characteristic function. 2) this binary function is converted into a volume array corresponding to samples of a smooth implicit function. 3) this volumetric representation is converted into a multiscale B-spline model. This method is based on wavelet analysis and synthesis techniques and is very general. It can convert to implicit form any geometric object that is suitable for discretization into a characteristic function.
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.
Blob Metamorphosis based on Minkowski Sums
(Blackwell Science Ltd and the Eurographics Association, 1996) Galin, E.; Akkouche, S.
This paper addresses the metamorphosis of soft objects built from skeletons. We propose a new approach that may be split into three steps. The first step consists in an original splitting of the initial and the final shapes with a view to creating a bijective graph of correspondence. In the second step, we assume that the skeletons are convex polygonal shapes, and thus take advantage of the properties of Minkowski sums to characterize the skeletons of intermediate shapes. Eventually, we characterize the intermediate distance and field functions- we describe a set of interpolation methods and propose to use a restricted class of parametrized distance and field functions so as to preserve coherence and speed-up computations.We show that we can easily extend those results to achieve a Bezier like metamorphosis where control points are replaced by control soft objects- in this scope, we have adapted existing accelerated techniques that build a Bezier transformation from a set of convex polyhedra to any kind of convex polygonal shapes.Eventually, we point out that matching all components of the initial and the final shapes generates amorphous intermediate shapes based on an overwhelming number of intermediate sub-components. Thus, we propose heuristics with a view to preserving coherence during the transformation and accelerating computations. We have implemented and tested our techniques in an experimental ray-tracer.
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.
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.
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.
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.
Data Dependent Thin Plate Energy and its use in Interactive Surface Modeling
(Blackwell Science Ltd and the Eurographics Association, 1996) Greiner, Gunther; Loos, Joachim; Wesselink, Wieger
When modeling spline surfaces of complex shape, one has to deal with an overwhelming number of control points. Modeling by direct manipulation of the control points is a tedious task. In particular, it is very difficult to maintain a generally pleasant looking surface shape. It becomes therefore increasingly important to build tools that allow the designer to specify only a few geometric constraints while automatically determining the explicit representation of the surface. The basic concept of such a tool is simple. In a first step one has to somehow measure the"fairness" (=quality) of a surface. Once this is achieved, an optimization process selects the one surface with optimal fairness from all surfaces satisfying the user specified geometric constraints.To measure the fairness, thin plate energy functionals are a good choice. However, for interactive use these functionals are far too complex. W e will present appropriate approximations to these functionals that allow an optimization nearly in real time. Thefunctionals are obtained by introducing reference surfaces thus leading to data dependent, quadratic approximations to the exact thin plate energy functionals. We apply the method to interactive surface manipulations based on energy constraints.
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.
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.
An Efficient Algorithm for Line Clipping by Convex and Non-convex Polyhedra in E3
(Blackwell Science Ltd and the Eurographics Association, 1996) Skala, Vaclav
A new algorithm for clipping lines against convex polyhedron with O(N) complexity is given with modification for non-convex polyhedron. The suggested algorithm is faster for higher number of facets of the given polyhedron than the traditional Cyrus-Beck s algorithm. Some principal results of comparison of all algorithms are shown and give some ideas how the proposed algorithm could be used effectively.
Efficient Hierarchical Refinement and Clustering for Radiosity in Complex Environments
(Blackwell Science Ltd and the Eurographics Association, 1996) Gibson, S.; Hubbold, R.J.
Generating accurate radiosity solutions of very complex environments is a time-consuming problem. We present a rapid hierarchical algorithm that enables such solutions to be computed quickly and efficiently. Firstly, a new technique for bounding the error in the transfer of radiosity between surfaces is discussed, incorporating bounds on form factors, visibility, irradiance, and reflectance over textured surfaces. This technique is then applied to the problem of bounding radiosity transfer between clusters of surfaces, leading to a fast, practical clustering algorithm that builds on the previous work of Sillion1. Volumes are used to represent clusters of small surfaces, but unlike previous algorithms, the orientations of surfaces inside each cluster are accounted for in both the error bound and radiosity transfer. This enables an accurate solution to be generated very efficiently, and results are presented demonstrating the performance of the algorithm on a variety of complex models, one containing almost a quarter of a million initial surfaces.
Efficient Lossless Image Contour Coding
(Blackwell Science Ltd and the Eurographics Association, 1996) Turner, Martin J.; Wiseman, Neil E.
A process is presented for converting a raster image into a discrete set of plateaus or contours. A contour coder has been developed which fully describes these contours via their boundary descriptions in a compact and computationally efficient manner, and is the basis for an image compression method. An analysis of some of the possible edge coding schemes is presented with both theoretical and practical conclusions. Described is a detailed study of the problems encountered and solutions chosen.
Energy Duality Methods for Piecewise Bezier Curve Construction
(Blackwell Science Ltd and the Eurographics Association, 1996) Bercovier, M.; Volpin, O.
Piecewise Bezier Curves are constructed using a minimization principle. Ck and GCk continuity is imposed by linear constraints. The corresponding quadratic programming with linear constraints problem is introduced and solved by duality methods. Bordering matrices methods are implemented to deal with local refinement (subdivision). The result is a versatile tool for defining/editing contours made of piecewise Bezier curves.

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