The Experts below are selected from a list of 28539 Experts worldwide ranked by ideXlab platform
Changhun Kim - One of the best experts on this subject based on the ideXlab platform.
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a robust reconstruction algorithm of displaced butterfly subdivision surfaces from unorganized points
Lecture Notes in Computer Science, 2003Co-Authors: Byeongseon Jeong, Sun Jeong Kim, Changhun KimAbstract:This paper presents a more robust reconstruction algorithm to solve the genus restriction of displaced subdivision surface (DSS) from unorganized points. DSS is a useful mesh representation to guarantee the memory efficiency by storing a vertex position as one scalar displacement value, which is measured from the original mesh to its Parametric Domain. However, reconstructing DSS from unorganized points has some defects such as the incorrect approximation of concave region and the limited application of genus-0. Based on volumetric approach, our new cell carving method can easily and quickly obtain the shape of point clouds and preserve its genus. In addition, using interpolatory subdivision scheme, our displaced butterfly subdivision surface is also effective multiresolution representation, because it samples exclusively new odd vertices at each level, compared with previous works to resample all vertices of every level. We demonstrate that displaced butterfly subdivision surface is an effective multiresolution representation that overcome the topological restriction and preserve the detailed features nicely.
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direct reconstruction of displaced subdivision surface from unorganized points
Pacific Conference on Computer Graphics and Applications, 2001Co-Authors: Wonki Jeong, Changhun KimAbstract:We propose a new mesh reconstruction algorithm that produces a displaced subdivision mesh directly from unorganized points. The displaced subdivision surface is a new mesh representation that defines a detailed mesh with a displacement map over a smooth Domain surface. This mesh representation has several benefits-compact mesh size, piecewise regular connectivity-to overcome limitations of an irregular mesh produced by an ordinary mesh reconstruction scheme, but the original displaced subdivision surface generation algorithm needs an explicit polygonal mesh to be converted. Our approach is producing displaced subdivision surface directly from input points during the mesh reconstruction process. The main ideas of our algorithm are building initial coarse control mesh by the shrink-wrapping like projection and sampling fine surface detail from unorganized points along the each limit vertex normal without any connectivity information of given points. We employ an existing subdivision surface fitting scheme to generate a Parametric Domain surface, and suggest a surface detail sampling scheme that determines a valid sampling triangle which can be made with combinations of input points. We show several reconstruction examples and applications to show the validity of suggested sampling technique and benefits of the result like multiresolution modeling.
Hong Qin - One of the best experts on this subject based on the ideXlab platform.
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surface mesh to volumetric spline conversion with generalized polycubes
IEEE Transactions on Visualization and Computer Graphics, 2013Co-Authors: Kexiang Wang, Hong QinAbstract:This paper develops a novel volumetric parameterization and spline construction framework, which is an effective modeling tool for converting surface meshes to volumetric splines. Our new splines are defined upon a novel Parametric Domain called generalized polycubes (GPCs). A GPC comprises a set of regular cube Domains topologically glued together. Compared with conventional polycubes (CPCs), the GPC is much more powerful and flexible and has improved numerical accuracy and computational efficiency when serving as a Parametric Domain. We design an automatic algorithm to construct the GPC Domain while also permitting the user to improve shape abstraction via interactive intervention. We then parameterize the input model on the GPC Domain. Finally, we devise a new volumetric spline scheme based on this seamless volumetric parameterization. With a hierarchical fitting scheme, the proposed splines can fit data accurately using reduced number of superfluous control points. Our volumetric modeling scheme has great potential in shape modeling, engineering analysis, and reverse engineering applications.
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technical section a divide and conquer approach for automatic polycube map construction
Computers & Graphics, 2009Co-Authors: Hongyu Wang, Hong QinAbstract:Polycube map is a global cross-surface parameterization technique, where the polycube shape can roughly approximate the geometry of modeled objects while retaining the same topology. The large variation of shape geometry and its complex topological type in real-world applications make it difficult to effectively construct a high-quality polycube that can serve as a good global Parametric Domain for a given object. In practice, existing polycube map construction algorithms typically require a large amount of user interaction for either pre-constructing the polycubes with great care or interactively specifying the geometric constraints to arrive at the user-satisfied maps. Hence, it is tedious and labor intensive to construct polycube maps for surfaces of complicated geometry and topology. This paper aims to develop an effective method to construct polycube maps for surfaces with complicated topology and geometry. Using our method, users can simply specify how close the target polycube mimics a given shape in a quantitative way. Our algorithm can both construct a similar polycube of high geometric fidelity and compute a high-quality polycube map in an automatic fashion. In addition, our method is theoretically guaranteed to output a one-to-one map. To demonstrate the efficacy of our method, we apply the automatically-constructed polycube maps in a number of computer graphics applications, such as seamless texture tiling, T-spline construction, and quadrilateral mesh generation.
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free form geometric modeling by integrating Parametric and implicit pdes
IEEE Transactions on Visualization and Computer Graphics, 2007Co-Authors: Hong QinAbstract:Parametric PDE techniques, which use partial differential equations (PDEs) defined over a 2D or 3D Parametric Domain to model graphical objects and processes, can unify geometric attributes and functional constraints of the models. PDEs can also model implicit shapes defined by level sets of scalar intensity fields. In this paper, we present an approach that integrates Parametric and implicit trivariate PDEs to define geometric solid models containing both geometric information and intensity distribution subject to flexible boundary conditions. The integrated formulation of second-order or fourth-order elliptic PDEs permits designers to manipulate PDE objects of complex geometry and/or arbitrary topology through direct sculpting and free-form modeling. We developed a PDE-based geometric modeling system for shape design and manipulation of PDE objects. The integration of implicit PDEs with Parametric geometry offers more general and arbitrary shape blending and free-form modeling for objects with intensity attributes than pure geometric models.
Rifat Sipahi - One of the best experts on this subject based on the ideXlab platform.
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an exact method for the stability analysis of time delayed linear time invariant lti systems
IEEE Transactions on Automatic Control, 2002Co-Authors: Nejat Olgac, Rifat SipahiAbstract:A general class of linear time invariant systems with time delay is studied. Recently, they attracted considerable interest in the systems and control community. The complexity arises due to the exponential type transcendental terms in their characteristic equation. The transcendentality brings infinitely many characteristic roots, which are cumbersome to elaborate as evident from the literature. A number of methodologies have been suggested with limited ability to assess the stability in the Parametric Domain of time delay. This study offers an exact, structured and robust methodology to bring a closure to the question at hand. Ultimately we present a unique explicit analytical expression in terms of the system parameters which not only reveals the stability regions (pockets) in the Domain of time delay, but it also declares the number of unstable characteristic roots at any given pocket. The method starts with the determination of all possible purely imaginary (resonant) characteristic roots for any positive time delay. To achieve this a simplifying substitution is used for the transcendental terms in the characteristic equation. It is proven that the number of such resonant roots for a given dynamics is finite. Each one of these roots is created by infinitely many time delays, which are periodically distributed. An interesting property is also claimed next, that the root crossing directions at these locations are invariant with respect to the delay and dependent only on the crossing frequency. These two unique findings facilitate a simple and practical stability method, which is the highlight of the work.
Kun Zhou - One of the best experts on this subject based on the ideXlab platform.
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geometrically nonlinear analysis of thin shell structures based on an isogeometric meshfree coupling approach
Computer Methods in Applied Mechanics and Engineering, 2018Co-Authors: Nhon Nguyenthanh, Kun ZhouAbstract:Abstract This paper develops a novel coupling approach of the isogeometric analysis (IGA) method and the meshfree method for geometrically nonlinear analysis of thin-shell structures. The Kirchhoff–Love (KL) thin-shell theory is employed without the consideration of rotational degrees of freedom. Both Parametric Domain and physical Domain are utilized for the thin-shell structures, and the former one is used to couple the IGA and meshfree methods and to obtain the later one via mapping. The Domain is divided into three subDomains: the subDomain described by the IGA method to ensure geometry exactness, the subDomain described by the meshfree method to achieve local refinement, and the coupling subDomain described by both methods. In the coupling subDomain, the reproducing points are obtained based on the consistency conditions to realize smoothness between the IGA and meshfree subDomains. The coupling approach can achieve a higher convergence rate than the IGA and meshfree methods because of the realization of local refinement. The accuracy and robustness of the coupling approach are validated by solving shell benchmark problems.
Wonki Jeong - One of the best experts on this subject based on the ideXlab platform.
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direct reconstruction of displaced subdivision surface from unorganized points
Pacific Conference on Computer Graphics and Applications, 2001Co-Authors: Wonki Jeong, Changhun KimAbstract:We propose a new mesh reconstruction algorithm that produces a displaced subdivision mesh directly from unorganized points. The displaced subdivision surface is a new mesh representation that defines a detailed mesh with a displacement map over a smooth Domain surface. This mesh representation has several benefits-compact mesh size, piecewise regular connectivity-to overcome limitations of an irregular mesh produced by an ordinary mesh reconstruction scheme, but the original displaced subdivision surface generation algorithm needs an explicit polygonal mesh to be converted. Our approach is producing displaced subdivision surface directly from input points during the mesh reconstruction process. The main ideas of our algorithm are building initial coarse control mesh by the shrink-wrapping like projection and sampling fine surface detail from unorganized points along the each limit vertex normal without any connectivity information of given points. We employ an existing subdivision surface fitting scheme to generate a Parametric Domain surface, and suggest a surface detail sampling scheme that determines a valid sampling triangle which can be made with combinations of input points. We show several reconstruction examples and applications to show the validity of suggested sampling technique and benefits of the result like multiresolution modeling.