Examinando por Materia "Color image processing"

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    Aspect ratio- and size-controlled patterned triangulations of parametric surfaces
    (ACTA PRESS ANAHEIM, 2007-01-01) Ruiz, Oscar E.; Pena, Sebastian; Duque, Juan; Universidad EAFIT. Departamento de Ingeniería Mecánica; Laboratorio CAD/CAM/CAE
    A method to produce patterned, controlled size triangulation of Boundary Representations is presented. Although the produced patterned triangulations are not immediately suited for fast visualization, they were used in Fixed Grid Finite Element Analysis, and do provide a control on the aspect ratio or shape factor of the triangles produced. The method presented first calculates a triangulation in the parameter space of the faces in which the B-Rep is partitioned and then maps it to 3D space. Special emphasis is set in ensuring that the triangulations of neighboring faces meet in a seamless manner, therefore ensuring that a borderless C2 2-manifold would have as triangulation a C0 borderless 2-manifold. The method works properly under the conditions (i) the parametric form of the face is a 1-1 function, (ii) the parametric pre-image of a parametric face is a connected region, and (iii) the user-requested sampling frequency ( samples per length unit ) is higher than twice the spatial frequency of the features in the B-Rep ( thus respecting the Nyquist principle ). As the conditions (i) and (ii) are possible under face reparameterization or sub-division and the condition (iii) is the minimum that a triangulation should comply with, the method is deemed as generally applicable.
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    Geometrical degeneracy removal by virtual disturbances - An application to surface reconstruction from point slice samples
    (INSTICC-INST SYST TECHNOLOGIES INFORMATION CONTROL & COMMUNICATION, 2008-01-01) Ruiz, Oscar; Vasquez, Eliana; Pena, Sebastian; Granados, Miguel; Universidad EAFIT. Departamento de Ingeniería Mecánica; Laboratorio CAD/CAM/CAE
    In surface reconstruction from slice samples (typical in medical imaging, coordinate measurement machines, stereolithography, etc.) the available methods attack the geometrical and topological properties of the surface. Topological methods classify the transitions occurred in the 2-manifold between two consecutive slices i and i+ 1. Geometrical methods synthesize the surface based on local proximity of the contours in consecutive slices. Superimposed 2D Voronoi Diagrams VDi and VDi+1 for slices i and i + 1, respectively, present topological problems if, for example, a site of VD i lies on an site or an edge of VDi+1. The usual treatment of this problem in literature is to apply a geometrical disturbance to either VDi or VDi+1, thus eliminating the degeneracy. In contrast, this article presents the implementation of a method which identifies the degenerate situation, constructs un-instantiated topological constructs, choses a geometrical instantiation based on a virtual disturbance introduced to the actual configuration. The algorithm was successfully applied to remove non-manifold topologies produced by well known algorithms in surface reconstruction.