Examinando por Materia "Image segmentation"

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    2D shape similarity as a complement for Voronoi-Delone methods in shape reconstruction
    (PERGAMON-ELSEVIER SCIENCE LTD, 2005-02-01) Ruiz, O.E.; Cadavid, C.A.; Granados, M.; Peña, S.; Vásquez, E.; Universidad EAFIT. Departamento de Ingeniería Mecánica; Laboratorio CAD/CAM/CAE
    In surface reconstruction from planar cross sections it is necessary to build surfaces between 2D contours in consecutive cross sections. This problem has been traditionally attacked by (i) direct reconstruction based on local geometric proximity between the contours, and (ii) classification of topological events between the cross sections. These approaches have been separately applied with limited success. In case (i), the resulting surfaces may have overstretched or unnatural branches. These arise from local contour proximity which does not reflect global similarity between the contours. In case (ii), the topological events are identified but are not translated into the actual construction of a surface. This article presents an integration of the approaches (i) and (ii). Similarity between the composite 2D regions bounded by the contours in consecutive cross sections is used to: (a) decide whether a surface should actually relate two composite 2D regions, (b) identify the type and location of topological transitions between cross sections and (c) drive the surface construction for the regions found to be related in step (a). The implemented method avoids overstretched or unnatural branches, rendering a surface which is both geometrically intuitive and topologically faithful to the cross sections of the original object. The presented method is a good alternative in cases in which correct reproduction of the topology of the surface (e.g. simulation of flow in conduits) is more important than its geometry (e.g. assessment of tumor mass in radiation planning). © 2004 Elsevier Ltd. All rights reserved.
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    Face reconstruction with structured light
    (INSTICC-INST SYST TECHNOLOGIES INFORMATION CONTROL & COMMUNICATION, 2011-01-01) Congote, J.; Barandiaran, I.; Barandiaran, J.; Nieto, M.; Ruiz, O.; Universidad EAFIT. Departamento de Ingeniería Mecánica; Laboratorio CAD/CAM/CAE
    This article presents a methodology for reconstruction of 3D faces which is based on stereoscopic images of the scene using active and passive surface reconstruction. A sequence of Gray patterns is generated, which are projected onto the scene and their projection recorded by a pair of stereo cameras. The images are rectified to make coincident their epipolar planes and so to generate a stereo map of the scene. An algorithm for stereo matching is applied, whose result is a bijective mapping between subsets of the pixels of the images. A particular connected subset of the images (e.g. the face) is selected by a segmentation algorithm. The stereo mapping is applied to such a subset and enables the triangulation of the two image readings therefore rendering the (x,y,z) points of the face, which in turn allow the reconstruction of the triangular mesh of the face. Since the surface might have holes, bilateral filters are applied to have the holes filled. The algorithms are tested in real conditions and we evaluate their performance with virtual datasets. Our results show a good reconstruction of the faces and an improvement of the results of passive systems.
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    Hybrid geometry / topology based mesh segmentation for reverse engineering
    (PERGAMON-ELSEVIER SCIENCE LTD, 2018-06-01) Mejia D.; Ruiz-Salguero O.; Sánchez J.R.; Posada J.; Moreno A.; Cadavid C.A.; Universidad EAFIT. Departamento de Ingeniería Mecánica; Laboratorio CAD/CAM/CAE
    Mesh segmentation and parameterization are crucial for Reverse Engineering (RE). Bijective parameterizations of the sub-meshes are a sine-qua-non test for segmentation. Current segmentation methods use either (1) topologic or (2) geometric criteria to partition the mesh. Reported topology-based segmentations produce large sub-meshes which reject parameterizations. Geometry-based segmentations are very sensitive to local variations in dihedral angle or curvatures, thus producing an exaggerated large number of small sub-meshes. Although small sub-meshes accept nearly isometric parameterizations, this significant granulation defeats the intent of synthesizing a usable Boundary Representation (compulsory for RE). In response to these limitations, this article presents an implementation of a hybrid geometry / topology segmentation algorithm for mechanical workpieces. This method locates heat transfer constraints (topological criterion) in low frequency neighborhoods of the mesh (geometric criterion) and solves for the resulting temperature distribution on the mesh. The mesh partition dictated by the temperature scalar map results in large, albeit parameterizable, sub-meshes. Our algorithm is tested with both benchmark repository and physical piece scans data. The experiments are successful, except for the well - known cases of topological cylinders, which require a user - introduced boundary along the cylinder generatrices. © 2018 Elsevier Ltd
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    Ítem
    Hybrid geometry / topology based mesh segmentation for reverse engineering
    (PERGAMON-ELSEVIER SCIENCE LTD, 2018-06-01) Mejia D.; Ruiz-Salguero O.; Sánchez J.R.; Posada J.; Moreno A.; Cadavid C.A.; Mejia D.; Ruiz-Salguero O.; Sánchez J.R.; Posada J.; Moreno A.; Cadavid C.A.; Universidad EAFIT. Departamento de Ciencias; Matemáticas y Aplicaciones
    Mesh segmentation and parameterization are crucial for Reverse Engineering (RE). Bijective parameterizations of the sub-meshes are a sine-qua-non test for segmentation. Current segmentation methods use either (1) topologic or (2) geometric criteria to partition the mesh. Reported topology-based segmentations produce large sub-meshes which reject parameterizations. Geometry-based segmentations are very sensitive to local variations in dihedral angle or curvatures, thus producing an exaggerated large number of small sub-meshes. Although small sub-meshes accept nearly isometric parameterizations, this significant granulation defeats the intent of synthesizing a usable Boundary Representation (compulsory for RE). In response to these limitations, this article presents an implementation of a hybrid geometry / topology segmentation algorithm for mechanical workpieces. This method locates heat transfer constraints (topological criterion) in low frequency neighborhoods of the mesh (geometric criterion) and solves for the resulting temperature distribution on the mesh. The mesh partition dictated by the temperature scalar map results in large, albeit parameterizable, sub-meshes. Our algorithm is tested with both benchmark repository and physical piece scans data. The experiments are successful, except for the well - known cases of topological cylinders, which require a user - introduced boundary along the cylinder generatrices. © 2018 Elsevier Ltd
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    Mesh Segmentation and Texture Mapping for Dimensional Inspection inWeb3D
    (Association for Computing Machinery, Inc, 2017-01-01) Mejia D.; Sánchez J.R.; Segura Á.; Ruiz-Salguero O.; Posada J.; Cadavid C.; Universidad EAFIT. Departamento de Ingeniería Mecánica; Laboratorio CAD/CAM/CAE
    Traditionally, the data generated by industrial metrology so.ware is stored as static reports that metrology experts produce for engineering and production departments. Nevertheless, industry demands new approaches that provide ubiquitous and real time access to overall geometry, manufacturing and other data. Web3D technologies can help to improve the traditional metrology methods and o.er new ways to convey this information in web-based continuous friendly manner. However, enriched point clouds may be massive, thus presenting transmission and display limitations. To partially overcome these limitations, this article presents an algorithm that computes efficient metrology textures, which are then transferred and displayed through Web3D standards. Texture coordinates are computed only once for the reference CAD mesh on the server using in-house thermal-based segmentation and Hessian-based parameterization algorithms. The metrology data is then encoded in a texture le, which becomes available instantly for interactive visual inspection through the Web3D platform. © 2017 ACM.
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    Monoscopic multifocus in polarization images for biological samples segmentation
    (OSA - The Optical Society, 2018-01-01) Cano C.; Restrepo R.; Universidad EAFIT. Departamento de Ciencias Básicas; Óptica Aplicada
    We present an implementation based on polarization images acquisition for different focus planes in a microscope, allowing the volumetric segmentation of structured biological samples like onion cellular walls. © 2018 The Author (s)
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    Numerical estimation of carbonate properties using a digital rock physics workflow
    (EAGE Publishing BV, 2014-01-01) Osorno, M.; Uribe, D.; Saenger, E.H.; Madonna, C.; Steeb, H.; Ruiz, O.; Universidad EAFIT. Departamento de Ingeniería Mecánica; Laboratorio CAD/CAM/CAE
    Digital rock physics combines modern imaging with advanced numerical simulations to analyze the physical properties of rocks. In this paper we suggest a special segmentation procedure which is applied to a carbonate rock from Switzerland. Starting point is a CT-scan of a specimen of Hauptmuschelkalk. The first step applied to the raw image data is a non-local mean filter. We then apply different thresholds to identify pores and solid phases. Because we are aware of a non-neglectable amount of unresolved microporosity we also define intermediate phases. Based on this segmentation determine porosity-dependent values for the p-wave velocity and for the permeability. The porosity measured in the laboratory is then used to compare our numerical data with experimental data. We observe a good agreement. Future work includes an analytic validation to the numerical results of the p-wave velocity upper bound, employing different filters for the image segmentation and using data with higher resolution.
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    On the estimation of extreme directional multivariate quantiles
    (Marcel Dekker Inc., 2019-01-01) Torres R.; Di Bernardino E.; Laniado H.; Lillo R.E.; Universidad EAFIT. Escuela de Ciencias; Modelado Matemático
    In multivariate extreme value theory (MEVT), the focus is on analysis outside of the observable sampling zone, which implies that the region of interest is associated to high risk levels. This work provides tools to include directional notions into the MEVT, giving the opportunity to characterize the recently introduced directional multivariate quantiles (DMQ) at high levels. Then, an out-sample estimation method for these quantiles is given. A bootstrap procedure carries out the estimation of the tuning parameter in this multivariate framework and helps with the estimation of the DMQ. Asymptotic normality for the proposed estimator is provided and the methodology is illustrated with simulated data-sets. Finally, a real-life application to a financial case is also performed. © 2019, © 2019 Taylor & Francis Group, LLC.