Issue 3

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https://diglib.eg.org/handle/10.2312/80

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Now showing 1 - 20 of 41

An Algorithmic Reflectance and Transmittance Model for Plant Tissue
(Blackwell Publishers Ltd and the Eurographics Association, 1997) Baranoski, Gladimir V.G.; Rokne, Jon G.
Recent developments in rendering have provided very realistic images. However, these images rarely show organic objects. We believe that one of the main difficulties of rendering these objects realistically is the lack of reflectance and transmittance models oriented to organic materials. In this paper an algorithmic reflectance and transmittance model for plant tissue oriented to computer graphics applications is presented. The model accounts for the three components of light propagation in plant tissues, namely surface reflectance, subsurface reflectance and transmittance, and mechanisms of light absorption by pigments present in these tissues. The model design is based on the available biological information, and it is controlled by a small number of biologically meaningful parameters. Its formulation, based on standard Monte Carlo techniques, guarantees its easy incorporation into most rendering systems. The spectral curves of reflectance and transmittance computed by the model are compared with measured curves from actual experiments.
An Analysis of Quasi-Monte Carlo Integration Applied to the Transillumination Radiosity Method
(Blackwell Publishers Ltd and the Eurographics Association, 1997) Szirmay-Kalos, Laszlo; Foris, Tibor; Neumann, Laszlo; Csebfalvi, Balazs
This paper presents an enhanced transillumination radiosity method that can provide accurate solutions at relatively low computational cost. The proposed algorithm breaks down the double integral of the gathered power to an area integral that is computed analytically and to a directional integral that is evaluated by quasi-Monte Carlo techniques. Since the analytical integration results in a continuous function of finite variation, the quasi-Monte Carlo integration that follows the analytical integration will be efficient and its error can be bounded by the Koksma-Hlawka inequality. The paper also analyses the requirements of the convergence, presents theoretical error bounds and proposes error reduction techniques. The theoretical bounds are compared with simulation results.
Animation by Deformation of Space-Time Objects
(Blackwell Publishers Ltd and the Eurographics Association, 1997) Aubert, Fabrice; Bechmann, Dominique
This article presents the properties of animation with space-time objects. A space-time object means here a geometrical object embedded in R4 with a volumic topology. Resulting animations are obtained by deforming space-time objects with a free-form deformation model. In this way topological modifications, such as disconnecting or hole making, as well as classical geometrical modifications, can be created in an animated object.
Automatic Hierarchical Level of Detail Optimization in Computer Animation
(Blackwell Publishers Ltd and the Eurographics Association, 1997) Mason, Ashton E.W.; Blake, Edwin H.
We show that the hierarchical level of detail optimization problem is equivalent to a constrained version of the Multiple Choice Knapsack Problem, and present a new algorithm whose solution to it is at least half as good as the optimal one. The advantage of the hierarchical algorithm is that it allows the use of hierarchical level of detail descriptions in which shared representations may be provided for groups of objects. Rendering cost may then be saved to afford better renderings of more important objects, and the algorithm is capable of providing a complete representation of the visible scene even when the visible scene complexity is very high. Our algorithm has a worst case time complexity of O(nlogn), and is incremental so that it typically completes in only a few iterations. We introduce the use of perceptual evaluation to demonstrate the effectiveness of the use of representations for groups of objects that our algorithm allows.
Bounded Radiosity - Illumination on General Surfaces and Clusters
(Blackwell Publishers Ltd and the Eurographics Association, 1997) Stamminger, Marc; Slusallek, Philipp; Seidel, Hans-Peter
Traditionally, Radiosity algorithms have been restricted to scenes made from planar patches. Most algorithms for computing form factors and the subdivision criterion for hierarchical methods implicitly assume planar patches. In this paper, we present a new radiosity algorithm that is solely based on simple geometric information about surface elements, namely their bounding boxes and cone of normals. Using this information allows to compute efficient error bounds that can be used for the subdivision oracle and for computing the energy transfer. Due to the simple interface to geometric objects, our algorithm not only allows for computing illumination on general curved surfaces, but it can also be directly applied to a hieararchy of clusters. Several examples demonstrate the advantages of the new approach.
Building Telepresence Systems: Translating Science Fiction Ideas into Reality
(Blackwell Publishers Ltd and the Eurographics Association, 1997) Fuchs, Henry
Many people feel that at some time in the distant future it will be possible to see and interact with remote individuals so realistically that they will appear to be standing next to us, that it will also be possible for physicians to look inside their patients and see organs and tumors, as if they possessed Supermanâ s X-ray vision.Although we are far from the realization of such dreams, we are witnessing some encouraging progress toward them. For example, we understand that two aspects common to these systems are a) the acquisition and synthesis of complex 3D information (whether from cameras at a distant scene or medical imaging devices inside a patient), and b) reconstruction and presentation of the 3D information to the observer (whether a distant collaborator or a nearby physician). Early results from several institutions are encouraging.It is now possible to walk around distant scenes, although the visual data still needs to be preprocessed, the scene still needs to be static and the reconstruction still has gaps. It is possible to look inside patients, although with crude ultrasound imaging and with very limited visualization, or not naturally from the physicianâ s own point of view. It is not yet possible to view any of this kind of information with high degree of immersive 3D realism without wearing cumbersome visualization aids. Truly compelling realization of these long-held dreams will take careful analysis of the remaining problems, creative thinking about new approaches, and innovative and sustained development of the required acquisition and display technologies.
Compression Domain Volume Rendering for Distributed Environments
(Blackwell Publishers Ltd and the Eurographics Association, 1997) Lippert, L.; Gross, M.H.; Kurmann, C.
This paper describes a method for volume data compression and rendering which bases on wavelet splats. The underlying concept is especially designed for distributed and networked applications, where we assume a remote server to maintain large scale volume data sets, being inspected, browsed through and rendered interactively by a local client. Therefore, we encode the serverâ s volume data using a newly designed wavelet based volume compression method. A local client can render the volumes immediately from the compression domain by using wavelet footprints, a method proposed earlier. In addition, our setup features full progression, where the rendered image is refined progressively as data comes in. Furthermore, framerate constraints are considered by controlling the quality of the image both locally and globally depending on the current network bandwidth or computational capabilities of the client. As a very important aspect of our setup, the client does not need to provide storage for the volume data and can be implemented in terms of a network application. The underlying framework enables to exploit all advantageous properties of the wavelet transform and forms a basis for both sophisticated lossy compression and rendering. Although coming along with simple illumination and constant exponential decay, the rendering method is especially suited for fast interactive inspection of large data sets and can be supported easily by graphics hardware.
Computing Volumes of Solids Enclosed by Recursive Subdivision Surfaces
(Blackwell Publishers Ltd and the Eurographics Association, 1997) Peters, Jorg; Nasri, Ahmad
The volume of a solid enclosed by a recursive subdivision surface can be approximated based on the closed-form representation of regular parts of the subdivision surface and a tight estimate of the local convex hull near extraordinary points. The approach presented is efficient, i.e. non-exponential, and robust in that it yields rapidly contracting error bounding boxes. An extension to measuring higher-order moments is sketched.
Deformable Surface Techniques for Field Visualization
(Blackwell Publishers Ltd and the Eurographics Association, 1997) Sadarjoen, I.; Post, Frits H.
Surface extraction from data fields is often used in scientific visualization, as surfaces can represent meaningful information and they are well suited for display. This paper describes a general method for localized surface extraction from scalar and vector fields. An initial polygonal surface is placed within the field, and the shape of the surface is adapted to the field by iterative displacement of surface nodes according to a displacement criterion. To achieve a good approximation of a smooth surface, the polygon mesh can be locally refined during iteration. The type of surface extracted depends on the displacement criterion, which can be any function of the available field variables. Techniques for displacement and mesh refinement are discussed in detail. The results we show are generation of a local isosurface and extraction of a vortex tube. Finally, we will draw conclusions and discuss some issues for further development.
Efficient Impostor Manipulation for Real-Time Visualization of Urban Scenery
(Blackwell Publishers Ltd and the Eurographics Association, 1997) Sillion, Francois; Drettakis, George; Bodelet, Benoit
Urban environments present unique challenges to interactive visualization systems, because of the huge complexity of the geometrical data and the widely varying visibility conditions. This paper introduces a new framework for real-time visualisation of such urban scenes. The central concept is that of a dynamic segmentation of the dataset, into a local three-dimensional model and a set of impostors used to represent distant scenery. A segmentation model is presented, based on inherent urban structure. A new impostor structure is introduced, derived from the level-of-detail approach. Impostors combine three-dimensional geometry to correctly model large depth discontinuities and parallax, and textures to rapidly display visual detail. We present the algorithms necessary for the creation of accurate and efficient three-dimensional impostors. The implementation of our algorithms allows interactive navigation in complex urban databases, as required by many applications.
Fast Analytic Shading and Shadowing for Area Light Sources
(Blackwell Publishers Ltd and the Eurographics Association, 1997) Tanaka, Toshimitsu; Takahashi, Tokiichiro
This paper describes a fast analytic algorithm that generates exact highlights and soft shadows from area light sources. In order to realize fast shadowing, we propose the ray-oriented buffer which segments 3D space by following light rays from polygonal sources. Each cell of the buffer stores objects that intersect a related subspace. Candidate objects which may cast shadows onto a point are selected by referring to the buffer. The candidates are then tested with their shadow bounding volumes to suppress objects that never occlude light sources.In addition, we propose the cross scanline clipping algorithm. It quickly determines the exact regions of uncovered area light sources with simple silhouette generation. Both diffuse and specular reflections are computed by integrating light rays from the uncovered sources. Experimental results confirm the high performance of the proposed method.
Finally Everyone Can Work With Highly Complex 3D Models
(Blackwell Publishers Ltd and the Eurographics Association, 1997) Rossignac, Jarek
In the past, access to 3D databases was restricted to few specialists having the appropriate CAD skills, software, and graphics hardware.The availability of inexpensive graphics support on personal computers, the Internetâ s impact on private and commercial communication, and the emergence of multimedia standards provide the basis for linking CAD databases with other personal productivity and communication tools and for making them accessible to everyone at home, in schools, in hospitals, or in the industry. For example, employees that have no design expertise, customers, and suppliers would benefit from having an easy access to the 3D databases of a company for: collaborative design review, 3D-based multi-media problem reports, collaborative problem solving and tracking, online training and documentation, internet-based part purchasing and subcontracting, demonstration to customers, or advertising. This presentation will address three of the key issues that have so far limited the non-specialistâ s access to 3D databases.First-time or occasional non-expert users need to become instant experts in 3D navigation through Virtual Environments or in the interactive manipulation of digital 3D models, so that they may immediately focus on their tasks, and not waste precious time learning and fighting an unnatural user interface. Immersive VR is not the panacea - other more effective techniques show promise.The data complexity found in commercial CAD databases, especially in the automotive, aerospace, and construction industries, significantly exceeds the capabilities of any interactive graphics system. This situation is not likely to change, since the growth of the complexity and availability of 3D models outpaces the performance improvement of personal computers. Research on the automatic simplification of 3D models and on the use of levels of detail to accelerate the rendering of distant portions of the scene is growing rapidly.The still limited bandwidth of internet communication channels prohibits a pervasive access to large amounts of 3D data. Recent 3D compression techniques reduce the storage requirements for polyhedral 3D models by two orders of magnitudes.
A Flexible Architecture for Virtual Humans in Networked Collaborative Virtual Environments
(Blackwell Publishers Ltd and the Eurographics Association, 1997) Sunday Pandzic, Igor; Lee, Elwin; Magnenat Thalmann, Nadia; Capin, Tolga K.; Thalmann, Daniel
Complex virtual human representation provides more natural interaction and communication among participants in networked virtual environments, hence it is expected to increase the sense of being together within the same virtual world. We present a flexible framework for the integration of virtual humans in networked collaborative virtual environments. A modular architecture allows flexible representation and control of the virtual humans, whether they are controlled by a physical user using all sorts of tracking and other devices, or by an intelligent control program turning them into autonomous actors. The modularity of the system allows for fairly easy extensions and integration with new techniques making it interesting also as a testbed for various domains from "classic" VR to psychological experiments. We present results in terms of functionalities, example applications and measurements of performance and network traffic with an increasing number of participants in the simulation.
A Framework for Interacting with Paper
(Blackwell Publishers Ltd and the Eurographics Association, 1997) Robinson, Peter; Sheppard, Dan; Watts, Richard; Harding, Robert; Lay, Steve
This paper reports on ways of using digitised video from television cameras in user interfaces for computer systems. The DigitalDesk is built around an ordinary physical desk and can be used as such, but it has extra capabilities. A video camera mounted above the desk, pointing down at the work surface, is used to detect where the user is pointing and to read documents that are placed on the desk. A computer-driven projector is also mounted above the desk, allowing the system to project electronic objects onto the work surface and onto real paper documents. The animated paper documents project is considering particular applications of the technology in electronic publishing. The goal is to combine electronic and printed documents to give a richer presentation than that afforded by either separate medium.This paper describes the framework that has been developed to assist with the preparation and presentation of these mixed-media documents. The central component is a registry that associates physical locations on pieces of paper with actions. This is surrounded by a number of adaptors that assist with the creation of new documents either from scratch or by translating from conventional hypermedia, and also allow the documents to be edited. Finally the DigitalDesk itself identifies pieces of paper and animates them with the actions described in the registry.
Generating Reflected Directions from BRDF Data
(Blackwell Publishers Ltd and the Eurographics Association, 1997) Lalonde, Paul; Fournier, Alain
Monte-Carlo path tracing algorithms for computer graphics require that given an incident light ray at a surface an outgoing direction can be computed with a distribution given by the magnitude of the bidirectional reflectance distribution function (BRDF). For analytic reflectance functions this can be done using various techniques including inverting the function, or tabulating some representation of the inverse. However, measured BRDF data sets are too large for this to be practical.We present a method to generate reflection rays distributed according to the magnitude of the BRDF. The method relies on a wavelet-based representation of the BRDF. This representation is efficient and compact, allowing large, anisotropic measured BRDF data sets to be represented with a few thousand coefficients. In particular, we exploit the wavelet representation to quickly compute integrals over ranges of the BRDF.
Growing and Animating Polygonal Models of Animals
(Blackwell Publishers Ltd and the Eurographics Association, 1997) Walter, Marcelo; Fournier, Alain
While there exist many computer models of animal bodies, as polygonal meshes and parametric surfaces, these are difficult to modify to take growth into account, or to animate. Growth data available from the literature usually is expressed as very sparse measurements over the body at various ages of the animal. We present here basic techniques to transfer growth data to computer models (especially polygonal meshes), which allows animation of the growth as well as animation of the body in the traditional sense.The main technique consists of defining local coordinate systems around the growing parts of the body, each one being transformed according to the relevant growth data while maintaining their relationship with the adjoining parts and the continuity of the surface. The local coordinates also permit ordinary animation mainly as relative rotation such as in articulated objects.We present examples with polygonal models of horses and cows, growth data from same, and motion from Muybridgeâ s classic photographic data.
Interactive Boundary Computation of Boolean Combinations of Sculptured Solids
(Blackwell Publishers Ltd and the Eurographics Association, 1997) Krishnan, S.; Gopi, M.; Manocha, D.; Mine, M.
We present algorithms and systems for interactive boundary computation of Boolean combinations of sculptured solids. The algorithm is applicable to all spline solids and computes an accurate boundary representation. To speed up the computation, the algorithm exploits parallelism at all stages. It has been implemented on a multi-processor SGI and takes one second on average per boolean operation to compute the boundary of high degree primitives. The system has also been integrated with an immersive design and manipulation environment. The resulting system is able to interactively evaluate boundaries of the models, display them for model validation and place them at appropriate position using collision detection algorithms.
Interactive High-Quality Soft Shadows in Scenes with Moving Objects
(Blackwell Publishers Ltd and the Eurographics Association, 1997) Loscos, Celine; Drettakis, George
Interactive rendering of soft shadows (or penumbra) in scenes with moving objects is a challenging problem. High quality walkthrough rendering of static scenes with penumbra can be achieved using pre-calculated discontinuity meshes, which provide a triangulation well adapted to penumbral boundaries, and backprojections which provide exact illumination computation at vertices very efficiently. However, recomputation of the complete mesh and back-projection structures at each frame is prohibitively expensive in environments with changing geometry. This recomputation would in any case be wasteful: only a limited part of these structures actually needs to be recalculated. We present a novel algorithm which uses spatial coherence of movement as well as the rich visibility information existing in the discontinuity mesh to avoid unnecessary recomputation after object motion. In particular we isolate all modifications required for the update of the discontinuity mesh by using an augmented spatial subdivision structure and we restrict intersections of discontinuity surfaces with the scene. In addition, we develop an algorithm which identifies visibility changes by exploiting information contained in the planar discontinuity mesh of each scene polygon, obviating the need for many expensive searches in 3D space. A full implementation of the algorithm is presented, which allows interactive updates of high-quality soft shadows for scenes of moderate complexity. The algorithm can also be directly applied to global illumination.
Interactive Rendering of Deforming NURBS Surfaces
(Blackwell Publishers Ltd and the Eurographics Association, 1997) Li, Frederick W. B.; Lau, Rynson W. H.; Green, Mark
Non-uniform rational B-splines (NURBS) has been widely accepted as a standard tool for geometry representation and design. Its rich geometric properties allow it to represent both analytic shapes and free-form curves and surfaces precisely. Moreover, a set of tools is available for shape modification or more implicitly, object deformation. Existing NURBS rendering methods include de Boor algorithm, Oslo algorithm, Shantzâ s adaptive forward differencing algorithm and Silbermannâ s high speed implementation of NURBS. However, these methods consider only speeding up the rendering process of individual frames. Recently, Kumar et al. proposed an incremental method for rendering NURBS surfaces, but it is still limited to static surfaces. In real-time applications such as virtual reality, interactive display is needed. If a virtual environment contains a lot of deforming objects, these methods cannot provide a good solution. In this paper, we propose an efficient method for interactive rendering of deformable objects by maintaining a polygon model of each deforming NURBS surface and adaptively refining the resolution of the polygon model. We also look at how this method may be applied to multi-resolution modelling.
A Million Polygons, a Million Pixels: Which is Heavier?
(Blackwell Publishers Ltd and the Eurographics Association, 1997) Sillion, Francois X.
The impressive progress of rendering software and hardware over the last two decades often leads to the - too rapid - conclusion that high-quality 3D imagery can now be incorporated in all sorts of applications. Interestingly, these advances allow more and more complex applications to be envisioned: however, an increase in processing power is not necessarily used to treat the same problem faster, but also creates a desire to attack larger problems. In many ways the models for visual simulation or engineering applications grow faster than the graphics systems! recent work on image-based rendering and modeling shows a growing awareness that traditional 3D methods may not scale well for the current and coming complexity levels.This talk will examine some of the challenges lying ahead for the development of future graphics applications. Specifically, when is it better to use pixels than polygons? when is a 3D model required? how can we mix and match competing approaches? can image-based approaches help for different applications such as lighting simulations? some issues related to network applications will also be discussed.

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