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Hierarchical Representation (hierarchical + representation)
Selected AbstractsFast display of large-scale forest with fidelityCOMPUTER ANIMATION AND VIRTUAL WORLDS (PREV: JNL OF VISUALISATION & COMPUTER ANIMATION), Issue 2 2006Huaisheng Zhang Abstract We propose a new hierarchical representation for a forest model, namely hierarchical layered depth mosaics (HLDM). Each node in the HLDM comprises a number of discrete textured quadrilaterals, called depth mosaics (DMs). The DMs are generated from the sampled depth images of the polygonal tree models. Meanwhile, their textures are compressed by a new approach accounting for occlusion. Our rendering procedure traverses the HLDM and renders the appropriate nodes according to a view-dependent selection criterion. A blending scheme is adopted to mitigate the visual ,popping' caused by the transition of levels of detail. The experiment demonstrates that the viewer could interactively walk or fly above the forest with fidelity. Copyright © 2006 John Wiley & Sons, Ltd. [source] Hierarchical Structure Recovery of Point-Sampled SurfacesCOMPUTER GRAPHICS FORUM, Issue 6 2010Marco Attene I.3 COMPUTER GRAPHICS; I.3.5 Computational Geometry and Object Modeling,Object hierarchies Abstract We focus on the class of ,regular' models defined by Várady et al. for reverse engineering purposes. Given a 3D surface,,represented through a dense set of points, we present a novel algorithm that converts,,to a hierarchical representation,. In,, the surface is encoded through patches of various shape and size, which form a hierarchical atlas. If,,belongs to the class of regular models, then,,captures the most significant features of,,at all the levels of detail. In this case, we show that,,can be exploited to interactively select regions of interest on,,and intuitively re-design the model. Furthermore,,,intrinsically encodes a hierarchy of useful ,segmentations' of,. We present a simple though efficient approach to extract and optimize such segmentations, and we show how they can be used to approximate the input point sets through idealized manifold meshes. [source] Practical modeling of molecular systems with symmetriesJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 9 2010Sergei Grudinin Abstract A new method for efficient modeling of macromolecular systems with symmetries is presented. The method is based on a hierarchical representation of the molecular system and a novel fast binary tree-based neighbor list construction algorithm. The method supports all types of molecular symmetry, including crystallographic symmetry. Testing the proposed neighbor list construction algorithm on a number of different macromolecular systems containing up to about 200,000 of atoms shows that (1) the current binary tree-based neighbor list construction algorithm scales linearly in the number of atoms for the central subunit, and sublinearly for its replicas, (2) the overall computational overhead of the method for a system with symmetry with respect to the same system without symmetry scales linearly with the cutoff value and does not exceed 50% for all but one tested macromolecules at the cutoff distance of 12 Ĺ. (3) the method may help produce optimized molecular structures that are much closer to experimentally determined structures when compared with the optimization without symmetry, (4) the method can be applied to models of macromolecules with still unknown detailed structure. © 2010 Wiley Periodicals, Inc. J Comput Chem, 2010 [source] A classification of mental models of undergraduates seeking information for a course essay in history and psychology: Preliminary investigations into aligning their mental models with online thesauriJOURNAL OF THE AMERICAN SOCIETY FOR INFORMATION SCIENCE AND TECHNOLOGY, Issue 13 2007Charles Cole The article reports a field study which examined the mental models of 80 undergraduates seeking information for either a history or psychology course essay when they were in an early, exploration stage of researching their essay. This group is presently at a disadvantage when using thesaurus-type schemes in indexes and online search engines because there is a disconnect between how domain novice users of IR systems represent a topic space and how this space is represented in the standard IR system thesaurus. The study attempted to (a) ascertain the coding language used by the 80 undergraduates in the study to mentally represent their topic and then (b) align the mental models with the hierarchical structure found in many thesauri. The intervention focused the undergraduates' thinking about their topic from a topic statement to a thesis statement. The undergraduates were asked to produce three mental model diagrams for their real-life course essay at the beginning, middle, and end of the interview, for a total of 240 mental model diagrams, from which we created a 12-category mental model classification scheme. Findings indicate that at the end of the intervention, (a) the percentage of vertical mental models increased from 24 to 35% of all mental models; but that (b) 3rd-year students had fewer vertical mental models than did 1st-year undergraduates in the study, which is counterintuitive. The results indicate that there is justification for pursuing our research based on the hypothesis that rotating a domain novice's mental model into a vertical position would make it easier for him or her to cognitively connect with the thesaurus's hierarchical representation of the topic area. [source] A NEW AGENT MATCHING SCHEME USING AN ORDERED FUZZY SIMILARITY MEASURE AND GAME THEORYCOMPUTATIONAL INTELLIGENCE, Issue 2 2008Hamed Kebriaei In this paper, an agent matching method for bilateral contracts in a multi-agent market is proposed. Each agent has a hierarchical representation of its trading commodity attributes by a tree structure of fuzzy attributes. Using this structure, the similarity between the trees of each pair of buyer and seller is computed using a new ordered fuzzy similarity algorithm. Then, using the concept of Stackelberg equilibrium in a leader,follower game, matchmaking is performed among the sellers and buyers. The fuzzy similarities of each agent with others in its personal viewpoint have been used as its payoffs in a bimatrix game. Through a case study for bilateral contracts of energy, the capabilities of the proposed agent-based system are illustrated. [source] Are Points the Better Graphics Primitives?COMPUTER GRAPHICS FORUM, Issue 3 2001Markus Gross Since the early days of graphics the computer based representation of three-dimensional geometry has been one of the core research fields. Today, various sophisticated geometric modelling techniques including NURBS or implicit surfaces allow the creation of 3D graphics models with increasingly complex shape. In spite of these methods the triangle has survived over decades as the king of graphics primitives meeting the right balance between descriptive power and computational burden. As a consequence, today's consumer graphics hardware is heavily tailored for high performance triangle processing. In addition, a new generation of geometry processing methods including hierarchical representations, geometric filtering, or feature detection fosters the concept of triangle meshes for graphics modelling. Unlike triangles, points have amazingly been neglected as a graphics primitive. Although being included in APIs since many years, it is only recently that point samples experience a renaissance in computer graphics. Conceptually, points provide a mere discretization of geometry without explicit storage of topology. Thus, point samples reduce the representation to the essentials needed for rendering and enable us to generate highly optimized object representations. Although the loss of topology poses great challenges for graphics processing, the latest generation of algorithms features high performance rendering, point/pixel shading, anisotropic texture mapping, and advanced signal processing of point sampled geometry. This talk will give an overview of how recent research results in the processing of triangles and points are changing our traditional way of thinking of surface representations in computer graphics - and will discuss the question: Are Points the Better Graphics Primitives? [source] Phylogenetic Species, Nested Hierarchies, and Character FixationCLADISTICS, Issue 4 2000Paul Z. Goldstein Cladistic mechanics and ramifications of various species concepts rooted in phylogenetic theory are explored. Published discussions of the phylogenetic species concept (PSC) have been hampered by persistent misconceptions surrounding its ontology and applicability, and by confusion of various incompatible versions of species concepts claiming to follow from Hennig's (1966), Phylogenetic Systematics, Univ. of Illinois Press, Urbana work. Especially problematic are topology- or tree-based versions of species diagnosis, which render diagnoses dependent on relationships depicted as hierarchically structured regardless of any lack of underlying hierarchy. Because the applicability of concepts such as monophyly, paraphyly, and polyphyly rests ultimately on the underlying hierarchical distribution of characters, representations of tokogenetic or reticulating systems as nested hierarchies are necessarily inaccurate. And since hierarchical representations,even if accurate,of nonrecombining genetic elements need not coincide with the organisms that bear them, tree-based diagnoses are further hampered, except potentially as retrospective tools. The relationship between tree-based species delineations and the criterion of character fixation is explored. Fixation of characters by which one identifies phylogenetic species is further distinguished from the fixation of character state differences, and the implications of that distinction are explored with reference to the interpretation of speciation events. It is demonstrated that character fixation in alternative species need not coincide with the achievement of reciprocal monophyly. While the PSC retains shortcomings, some of the more frequently criticized aspects of the PSC are functions of sampling that are no more problematic than for any basic systematic endeavor. [source] | ||||||||||||||||||||||