Issue 4

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https://diglib.eg.org/handle/10.2312/97

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    Automatic Creation of Object Hierarchies for Radiosity Clustering
    (Blackwell Publishers Ltd and the Eurographics Association, 2000) Muller, Gordon; Schafer, Stephan; Fellner, Dieter W.
    Using object clusters for hierarchical radiosity greatly improves the efficiency and thus usability of radiosity computations. By eliminating the quadratic starting phase very large scenes containing about 100k polygons can be handled efficiently. Although the main algorithm extends rather easily to using object clusters, the creation of 'good' object hierarchies is a difficult task both in terms of construction time and in the way how surfaces or objects are grouped to clusters. The quality of an object hierarchy for clustering depends on its ability to accurately simulate the hierarchy of the energy flow in a given scene. Additionally it should support visibility computations by providing efficient ray acceleration techniques.In this paper we will present a new approach of building hierarchies of object clusters. Our hybrid structuring algorithm provides accuracy and speed by combining a highly optimized bounding volume hierarchy together with uniform spatial subdivisions for nodes with regular object densities. The algorithm works without user intervention and is well suited for a wide variety of scenes. First results of using these hierarchies in a radiosity clustering environment are very promising and will be presented here.The combination of very deep hierarchies (we use a binary tree) together with an efficient ray acceleration structure shifts the computational effort away from form factor and visibility calculation towards accurately propagating the energy through the hierarchy. We will show how an efficient single pass gathering can be used to minimize traversal costs.
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    Announcements
    (Blackwell Publishers Ltd and the Eurographics Association, 2000)
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    Constructive Volume Geometry
    (Blackwell Publishers Ltd and the Eurographics Association, 2000) Chen, Min; Tucker, John V.
    We present an algebraic framework, called Constructive Volume Geometryn (CVG), for modelling complex spatial objects using combinational operations. By utilising scalar fields as fundamental building blocks, CVG provides high-level algebraic representations of objects that are defined mathematically or built upon sampled or simulated datasets. It models amorphous phenomena as well as solid objects, and describes the interior as well as the exterior of objects. We also describe a hierarchical representation scheme for CVG, and a direct rendering method with a new approach for consistent sampling. The work has demonstrated the feasibility of combining a variety of graphics data types in a coherent modelling scheme.
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    Event Reports
    (Blackwell Publishers Ltd and the Eurographics Association, 2000)
    Eurographics 2000Siggraph 2000
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    Versatile Tuning of Humanoid Agent Activity
    (Blackwell Publishers Ltd and the Eurographics Association, 2000) Emering, Luc; Boulic, Ronan; Molet, Tom; Thalmann, Daniel
    In this paper, we present an integration framework for heterogeneous motion generators. The objective is to outline issues that are currently easily solved in professional post-processing systems used in film and game production but which cannot be transposed as is to real-time systems with autonomous agents. We summarise our approach for articulated agent-modelling and their animation by combining heterogeneous motion generators, such as real-time motion capturing, key-framing, inverse kinematics, procedural walking. We propose an agent/action-oriented framework. Activity properties such as action simultaneity and motion blending, spatial coherence, motion-flow update schemes, agent attachments, and location corrections, are the main topics handled by our generic animation framework. Numerous examples throughout the paper illustrate our approach and outline encountered problems and solutions or open research directions.
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    Filtered Jitter
    (Blackwell Publishers Ltd and the Eurographics Association, 2000) Klassen, R. Victor
    Jitter is one popular way of generating samples for stochastic sampling in computer graphics. The Poisson disk distribution better approximates that of the human photomosaic. In this paper we examine the spatial and frequency space behaviour of a number of existing algorithms for generating stochastic samples and propose a new algorithm based on low pass filtering a jittered set of displacements. The distribution is at least as much like that of the human photomosaic as any existing algorithm, while being fast to compute.
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    Eurographics
    (Blackwell Publishers Ltd and the Eurographics Association, 2000)
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    Variable Resolution 4-k Meshes: Concepts and Applications
    (Blackwell Publishers Ltd and the Eurographics Association, 2000) Velho, Luiz; Gomes, Jonas
    In this paper we introduce variable resolution 4-k meshes, a powerful structure for the representation of geometric objects at multiple levels of detail. It combines most properties of other related descriptions with several advantages, such as more flexibility and greater expressive power. The main unique feature of the 4-k mesh structure lies in its variable resolution capability, which is crucial for adaptive computation. We also give an overview of the different methods for constructing the 4-k mesh representation, as well as the basic algorithms necessary to incorporate it in modeling and graphics applications.
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    Morphing the BlobTree
    (Blackwell Publishers Ltd and the Eurographics Association, 2000) Galin, Eric; Leclercq, Antoine; Akkouche, Samir
    Implicit surfaces have proved to be a particularly well suited and efficient model for animating and morphing shapes of arbitrary topologies. The BlobTree model is characterized as a hierarchical combination of skeletal primitives organized in a tree. The nodes hold blending, boolean and warping operators, which allows the design of complex objects.In this paper, we address the metamorphosis of the BlobTree. This appears a difficult task as the tree data-structures of the initial and final shapes are completely different in the general case, and consequently cannot be matched easily. We propose an original technique that solves the correspondence process and creates an intermediate generic BlobTree model whose instances interpolate the initial and final shapes.The animator may control the correspondence between features and can specify both the speed of transformation and the trajectory of the nodes and the leaves of the generic BlobTree model. This provides the end user with a tight control over the transformation so as to achieve good visual effects.
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    Editorial
    (Blackwell Publishers Ltd and the Eurographics Association, 2000) Coquillart, Sabine; Duke, David
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    A Hybrid Approach for Stroke-Based Letterform Composition Including Outline-Based Methods
    (Blackwell Publishers Ltd and the Eurographics Association, 2000) Schneider, Uwe
    For three decades a number of computer-aided systems have been developed in order to assist in the design of digital type. Even though some of them are used by typographers in commercial type design, they are not yet widely accepted. One reason is the lack of appropriate design metaphors in systems which provide low-level operations (e.g. the manipulation of outlines). Another reason is the lack of essential functionality in high-level approaches (not all characters can be modeled). While these two reasons correspond with the underlying paradigms of those systems, namely the outline and the stroke approach, the presented model provides a synthesis of both. By exploring the high-level semantics of the stroke-based paradigm, letterforms can be composed by individual strokes. Properties like round corners at stroke intersections, as they typically appear in the design of Western type, can be modeled via outline segments attached to the associated stroke elements. As a consequence, Latin characters as well as characters incorporating hand-written characters, like Kanji, can be expressed using a single model. These two classes of types are considered by the typographic community to be fundamentaly different.
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    Perceptual Principles and Computer Graphics
    (Blackwell Publishers Ltd and the Eurographics Association, 2000) May, Jon
    Now that technology allows us to present photorealistic animations of scenically lit objects acting in real-time, the problem of computer graphics has changed from making displays recognisable, to ensuring that users notice what they are intended to see, without being distracted by irrelevant information. Worse than that, the use of veridical displays that are intended to be lifelike runs the risk of introducing unpredictable sources of information, that can lead users to infer all sorts of unwanted details. Traditional visual theory, based upon bottom-up models of feature extraction from the retinal image, cannot inform us about these aspects of perception. Broader based cognitive theories are required that integrate visual perception with attention, memory, emotion and inference. Theories such as Barnard's Interacting Cognitive Subsystems enable phenomena such as change blindness and the craft principles of film editing to be interpreted within a common framework, supporting extrapolation to computer graphics.