Volume 15 (1996)

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Incremental Volume Rendering Using Hierarchical Compression
(Blackwell Science Ltd and the Eurographics Association, 1996) Haley, Michael B.; Blake, Edwin H.
We present a new algorithm here for efficient incremental rendering of volumetric datasets. The primary goal of this algorithm is to give average workstations the ability to efficiently render volume data received over relatively low bandwidth network links in such a way that rapid user feedback is maintained. Common limitations of workstation rendering of volume data include: large memory overheads, the requirement of expensive rendering hardware, and high speed processing ability. The rendering algorithm presented here overcomes these problems by making use of the efficient Shear-Warp Factorisation method which does not require specialised graphics hardware. However the original Shear-Warp algorithm suffers from a high memory overhead and does not provide for incremental rendering which is required should rapid user feedback be maintained. Our algorithm represents the volumetric data using a hierarchical data structure which provides for the incremental classification and rendering of volume data. This exploits the multiscale nature of the octree data structure. The algorithm reduces the memory footprint of the original Shear-Warp Factorisation algorithm by a factor of more than two, while maintaining good rendering performance. These factors make our octree algorithm more suitable for implementation on average desktop workstations for the purposes of interactive exploration of volume models over a network. Results from tests using typical volume datasets will be presented which demonstrate the ability of the algorithm to achieve high rendering rates for both incremental rendering and standard rendering while reducing the runtime memory requirements.
Implicit Sweep Objects
(Blackwell Science Ltd and the Eurographics Association, 1996) Crespin, Benoit; Blanc, Carole; Schlick, Christophe
Using a Convex Pyramid to Bound Surface Normal Vectors
(Blackwell Science Ltd and the Eurographics Association, 1996) Daniel, M.
Determining a tight bounding volume of all the surface normal vectors is of interest in surface modelling especially for intersection problems, in order to detect closed intersection curves. It is also important to determine quickly whether two such volumes intersect. This paper adresses both problems through the introduction of a pyramid with a convex planar base. For intersection problems, a different method has been proposed by M. Hohmeyer. The various solutions are discussed and compared.
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.
Generation of 3D Texture Using Multiple 2D Models Analysis
(Blackwell Science Ltd and the Eurographics Association, 1996) GHAZANFARPOUR, Djamchid; DISCHLER, Jean-Michel
Solid (30) texturing is commonly used in computer graphics for producing more realistic images. It is often more attractive than the conventional 20 texture mapping but remains more complex on some points. Its major difficulty concerns the generation of 30 texture in a general and efficient way. The well-known traditional procedural methods use generally a simplified mathematical model of a natural texture. No reliable way for the choice of the mathematical model parameters, which characterise directly the produced 30 texture, is given. Therefore, 30 texture generation becomes a more or less experimental process with these methods.Our recently published methodfor an automatic 30 texture generation avoids this problem by the use of the spectral analysis of one 2D model texture. The resulting 30 texture is of good quality but one open problem remains: the aspect of the produced texture cannot be fully controlled over the entire 30 space by only one 20 spectral analysis. This may be considered as a serious limitation for some kinds of textures representing important variations in any direction.In this paper we present a new and more powerful analytical approach for an automatic 30 texture generation. Contrarily to our previous method, this new approach is not exclusively based on the spectral analysis of only one 20 model. It uses two or three 2D models corresponding to different slices of a 30 texture block, so, the aspect of the produced 3D texture can be controlled more efficiently over the entire 30 space. In addition, a more efficient 30 texture antialiasing, well adapted to this new method is presented.
Physically-Based Deformations Constrained in Displacements and Volume
(Blackwell Science Ltd and the Eurographics Association, 1996) Promayon, E.; Baconnier, P.; Puech, C.
This paper presents a method of constraining physically-based deformable objects. In this method, an object can be defined locally in terms of kinetic and dynamic (mass, position, speed), and physical parameters (compressibility, elasticity, motor functioning). Several problems are solved: constant volume deformation, displacement constraints (fixed or moving required positions), and real object modelling. An object is described by a set of mass points on its contour. The evolution algorithm runs in two phases dealing successively with forces and constraints (which are presented as reaction forces).The main contribution of the method is the control of object volumes during evolution. We define a function that explicitly gives the inside volume of an object in order to use it as a constraint. Thus, the volume can be kept exactly constant during deformation without using an iterative process, in opposition to lagrangian approaches. Some results are illustrated by examples at the end of the paper.
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.
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.
Integrating Computer Animation and Multimedia
(Blackwell Science Ltd and the Eurographics Association, 1996) Preston, Martin; Hewitt, Terry
Pertinent Data for Modelling Pigmented Materials in Realistic Rendering
(Blackwell Science Ltd and the Eurographics Association, 1996) Callet, Patrick
This article discusses the important problem of determining pertinent data to describe a pigmented medium. The first part deals with optical characteristics of pigments and the general properties of binders and fillers. It also exposes the limits and conditions of applicability of single scattering. In the second part the connection between individual optical properties, size, and form of particles is made with phenomenological theories of multiple scattering in absorbing media, Progressively, it appears that pertinent data in realistic modelling are always in relation with true or effective complex refractive indices and size parameters.
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.
Interactive Rendering of CSG Models
(Blackwell Science Ltd and the Eurographics Association, 1996) Wiegand, T. E
We describe a CSG rendering algorithm that requires no evaluation of the CSG tree beyond normalization and pruning. It renders directly from the normalized CSG tree and primitives described (to the graphics system) by their facetted boundaries. It behaves correctly in the presence of user defined,"near" and"far" clipping planes. It has been implemented on standard graphics workstations using Iris GL1 and Open GL2 graphics libraries. Modestly sized models can be evaluated and rendered at interactive (less than a second per frame) speeds. We have combined the algorithm with an existing B-rep based modeller to provide interactive rendering of incremental updates to large models.
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.
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 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.
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.
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.
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.

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