Volume 18 (1999)

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Modelling and Rendering Graphics Scenes Composed of Multiple Volumetric Datasets
(Blackwell Publishers Ltd and the Eurographics Association, 1999) Leu, Adrian; Chen, Min
This paper presents a method for modelling graphics scenes consisting of multiple volumetric objects. A two-level hierarchical representation is employed, which enables the reduction of the overall storage consumption as well as rendering time. With this approach, different objects can be derived from the same volumetric dataset, and 2D images can be trivially integrated into a scene. The paper also describes an efficient algorithm for rendering such scenes on ordinary workstations, and addresses issues concerning memory requirements and disk swapping.
Virtual Dunhuang Art Cave: A Cave within a CAVE
(Blackwell Publishers Ltd and the Eurographics Association, 1999) Lutz, B.; Weintke, M.
Virtual Reality can present historical places in a three-dimensional and interactive way, giving visitors a photorealistic impression of objects. Not only existing scenarios can be shown, but VR can also be used to rebuild scenarios that were damaged or destroyed a long time ago, giving new life to the cultural heritage. We used Virtual Reality to present the Mogao Grottos in Dunhuang. This cave site is one of the most important cultural and religious places by the ancient Silk Road. The presentation is to give visitors the impression of visiting the cave site and provide information about the caves, paintings and statues in an interesting way. To achieve this, we developed a new, intuitive interaction paradigm, which enables the user to explore the caves. To give observers a photorealistic impression of the caves and to create a feeling of immersion, innovative rendering techniques were integrated.The resulting presentation combines Virtual Reality and archaeology to give tourists a realistic experience of this cave site and to support scientists in their research work.
Improved Laplacian Smoothing of Noisy Surface Meshes
(Blackwell Publishers Ltd and the Eurographics Association, 1999) Vollmer, J.; Mencl, R.; Muller, H.
This paper presents a technique for smoothing polygonal surface meshes that avoids the well-known problem of deformation and shrinkage caused by many smoothing methods, like e.g. the Laplacian algorithm. The basic idea is to push the vertices of the smoothed mesh back towards their previous locations. This technique can be also used in order to smooth unstructured point sets, by reconstructing a surface mesh to which the smoothing technique is applied. The key observation is that a surface mesh which is not necessarily topologically correct, but which can efficiently be reconstructed, is sufficient for that purpose.
Texturing 3D Models of Real World Objects from Multiple Unregistered Photographic Views
(Blackwell Publishers Ltd and the Eurographics Association, 1999) Neugebauer, Peter J.; Klein, Konrad
As the efficiency of computer graphic rendering methods is increasing, generating realistic models is now becoming a limiting factor. In this paper we present a new technique to enhance already existing geometry models of real world objects with textures reconstructed from a sparse set of unregistered still photographs. The aim of the proposed technique is the generation of nearly photo-realistic models of arbitrarily shaped objects with minimal effort. In our approach, we require neither a prior calibration of the camera nor a high precision of the user's interaction. Two main problems have to be addressed of which the first is the recovery of the unknown positions and parameters of the camera. An initial estimate of the orientation is calculated from interactively selected point correspondences. Subsequently, the unknown parameters are accurately calculated by minimising a blend of objective functions in a 3D-2D projective registration approach. The key point of the proposed method of registration is a novel filtering approach which utilises the spatial information provided by the geometry model. Second, the individual images have to be combined yielding a set of consistent texture maps. We present a robust method to recover the texture from the photographs thereby preserving high spatial frequencies and eliminating artifacts, particularly specular highlights. Parts of the object not seen in any of the photographs are interpolated in the textured model. Results are shown for three complex example objects with different materials and numerous self-occlusions.
An Informed Environment Dedicated to the Simulation of Virtual Humans in Urban Context
(Blackwell Publishers Ltd and the Eurographics Association, 1999) Farenc, Nathalie; Boulic, Ronan; Thalmann, Daniel
In this paper, we outline the creation of an Informed Environment, dedicated to urban life simulation.We propose methods and tools for creating and providing the information necessary for animating virtual humans in a city using an Informed Environment. The Informed Environment is based on a hierarchical decomposition of a urban scene into Environment Entities providing geometrical information as well as semantic notions, thus allowing a more realistic simulation of human behaviour. In this manner, virtual humans can integrate with a certain kind of urban knowledge.
Efficient and Handy Texture Mapping on 3D Surfaces
(Blackwell Publishers Ltd and the Eurographics Association, 1999) Matsushita, Kenji; Kaneko, Toyohisa
There has been a rapid technical progress in three-dimensional (3D) computer graphics. But gathering surface and texture data is yet a laborious task. This paper addresses the problem of mapping photographic images on the surface of a 3D object whose geometric data are already known. We propose an efficient and handy method for acquiring textures and mapping them precisely on the surface, employing a digital camera alone. We describe an algorithm for selecting a minimal number of camera positions that can cover the entire surface of a given object and also an algorithm to determine camera's position and direction for each photograph taken so as to paste it to the corresponding surfaces precisely. We obtained a matching accuracy within a pixel on a surface through three experimental examples, by which the practicability of our method is demonstrated.
A New Method of Image Mosaicking and Its Application to Cultural Heritage Representation
(Blackwell Publishers Ltd and the Eurographics Association, 1999) Cortelazzo, G.M.; Lucchese, L.
This paper presents an original two-step procedure for estimating projective transformations between pairs of images: first, the transformation between the images is approximated as an affine transformation; second, this estimate is refined into that of a projective transformation. This strategy for matching projective views is computationally very efficient. The proposed method can be applied both to mosaicking of high resolution images of planar textured objects (e.g., frescoes and paintings), with subpixel accuracy, and to construction of panoramic images. Practical examples of mosaicking of cultural heritage imagery obtained by using the presented procedure are discussed in the paper.
Book Reviews
(Blackwell Publishers Ltd and the Eurographics Association, 1999)
Books reviewed:Arlov, Laura. GUI Design for DummiesLeopoldseder, Hannes and Schopf, Christine (Editors). Cyberarts98Lorentz, H. A. On the Theory of the Reflection and Refraction of LightVince, John. Essential Virtual Reality FastJolion, J.-M. and Kropatsch, W. G. Graph-Based Representations in Pattern RecognitionKokaram, Anil C. Motion Picture Restoration: Digital Algorithms for Artefact Suppression in Degraded Motion Picture Film and Video
Modeling and Rendering Escher-Like Impossible Scenes
(Blackwell Publishers Ltd and the Eurographics Association, 1999) Savransky, Guillermo; Dimerman, Dan; Gotsman, Craig
Inspired by the drawings of "impossible" objects by artists such as M.C. Escher, we describe a mathematical theory which captures some of the underlying principles of their work. Using this theory, we show how impossible three-dimensional scenes may be modeled and rendered synthetically.
Wavelet-Based 3D Compression Scheme for Interactive Visualization of Very Large Volume Data
(Blackwell Publishers Ltd and the Eurographics Association, 1999) Ihm, Insung; Park, Sanghun
Interactive visualization of very large volume data has been recognized as a task requiring great effort in a variety of science and engineering fields. In particular, such data usually places considerable demands on run-time memory space. In this paper, we present an effective 3D compression scheme for interactive visualization of very large volume data, that exploits the power of wavelet theory. In designing our method, we have compromised between two important factors: high compression ratio and fast run-time random access ability. Our experimental results on the Visual Human data sets show that our method achieves fairly good compression ratios. In addition, it minimizes the overhead caused during run-time reconstruction of voxel values. This 3D compression scheme will be useful in developing many interactive visualization systems for huge volume data, especially when they are based on personal computers or workstations with limited memory.
Nonphotorealistic Rendering by Q-mapping
(Blackwell Publishers Ltd and the Eurographics Association, 1999) Hall, P.
We present Q-mapping which is a technique for rendering three-dimensional objects using nonphotorealistic cues, by applying Q-maps. Q-maps are three-dimensional textures that make marks on objects, and thus provide visual cues for shape, shade, and texture. Q-maps adapt to light intensity, typically by making more marks in darker areas. Q-maps can produce images with a very wide range of visual styles (e.g. half tone shading, and pen-and-ink colour wash). The primary contribution is that these styles reside in a single parametric space. Importantly this space includes photorealism as a style, which is therefore regarded as a special case of nonphotorealistic image rendering in general. We illustrate our explanation of Q-mapping using examples from scientific visualisation and computer graphics - and provide a gallery of images to show the versatility of the approach.
Stochastic Iteration for Non-diffuse Global Illumination
(Blackwell Publishers Ltd and the Eurographics Association, 1999) Szirmay-Kalos, Laszlo
This paper presents a single-pass, view-dependent method to solve the rendering equation, using a stochastic iterational scheme where the transport operator is selected randomly in each iteration. The requirements of convergence are given for the general case. To demonstrate the basic idea, a very simple,continuous random transport operator is examined, which gives back the light tracing algorithm incorporating Russian roulette. Then, a new mixed continuous and finite-element based iteration method is proposed, which uses ray-bundles to transfer the radiance in a single random direction. The resulting algorithm is fast, it provides initial results in seconds and accurate solutions in minutes and does not suffer from the error accumulation problem and the high memory demand of other finite-element and hierarchical approaches.
An Efficient and Flexible Perception Pipeline for Autonomous Agents
(Blackwell Publishers Ltd and the Eurographics Association, 1999) Bordeux, Christophe; Boulic, Ronan; Thalmann, Daniel
Agents in virtual environments require a combination of perception and action to behave in an autonomous way. We extend a software architecture for the management of actions blending, called AGENTlib, with a perception mechanism. The perception system provides a uniform interface to various techniques in the field of virtual perception, including synthetic vision, database access and perception persistency. We describe the framework we designed to efficiently filter valuable information from the scene and we address concerns about computation redundancy and data propagation through multiple filtering modules.
Event Reports
(Blackwell Publishers Ltd and the Eurographics Association, 1999)
Eurographics '99Eurographics '99 Awards10th Eurographics Workshop on RenderingSiggraph '992000 Cover Competition
A Practical Analysis of Clustering Strategies for Hierarchical Radiosity
(Blackwell Publishers Ltd and the Eurographics Association, 1999) Hasenfratz, Jean-Marc; Damez, Cyrille; Sillion, Francois; Drettakis, George
The calculation of radiant energy balance in complex scenes has been made possible by hierarchical radiosity methods based on clustering mechanisms. Although clustering offers an elegant theoretical solution by reducing the asymptotic complexity of the algorithm, its practical use raises many difficulties, and may result in image artifacts or unexpected behavior. This paper proposes a detailed analysis of the expectations placed on clustering and compares the relative merits of existing, as well as newly introduced, clustering algorithms. This comparison starts from the precise definition of various clustering strategies based on a taxonomy of data structures and construction algorithms, and proceeds to an experimental study of the clustering behavior for real-world scenes. Interestingly, we observe that for some scenes light is difficult to simulate even with clustering. Our results lead to a series of observations characterizing the adequacy of clustering methods for meeting such diverse goals as progressive solution improvement, efficient ray casting acceleration, and faithful representation of object density for approximate visibility calculations.
Multi-layered impostors for accelerated rendering
(Blackwell Publishers Ltd and the Eurographics Association, 1999) Decoret, Xavier; Sillion, Francois; Schaufler, Gernot; Dorsey, Julie
This paper describes the successful combination of pre-generated and dynamically updated image-based representations to accelerate the visualization of complex virtual environments. We introduce a new type of impostor, which has the desirable property of limiting de-occlusion errors to a user-specified amount. This impostor, composed of multiple layers of textured meshes, replaces the distant geometry and is much faster to draw. It captures the relevant depth complexity in the model without resorting to a complete sampling of the scene. We show that layers can be dynamically updated during visualization. This guarantees bounded scene complexity in each frame and also exploits temporal coherence to improve image quality when possible. We demonstrate the strengths of this approach in the context of city walkthroughs.
Eurographics
(Blackwell Publishers Ltd and the Eurographics Association, 1999)
Interactive Mechanical Design Variation for Haptics and CAD
(Blackwell Publishers Ltd and the Eurographics Association, 1999) Nelson, Donald D.; Cohen, Elaine
A fast design variation technique for mechanical systems is presented. It is used to interactively optimize mechanical characteristics while "self-assembling" or satisfying large systems of mechanical constraints. The high speed method is central to providing inverse dynamics force feedback in haptics and control applications. Performance advantages with the use of augmented coordinates for inverse dynamics of closed loop topologies are also noted. The interaction framework allows manipulation of complex assemblies while maintaining kinematically admissible configurations though linkage and joint limit constraints. Furthermore, design variables such as link length can be treated as free variables and optimized to meet design criteria such as assembly dexterity. Assemblies with flexible bodies fit naturally within this framework. Thus, the contribution of this paper is the advancement of techniques in augmented coordinates for the kinematic and force feedback interaction with virtual mechanical assembly design optimization at force control rates.
Editorial
(Blackwell Publishers Ltd and the Eurographics Association, 1999) Coquillart, Sabine; Seidel, Hans-Peter
Erratum
(Blackwell Publishers Ltd and the Eurographics Association, 1999)

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