Browsing by Author "Hitschfeld, N."

Now showing 1 - 5 of 5
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    A GIS-based urban and peri-urban landscape representation toolbox for hydrological distributed modeling
    (2017) Sanzana Cuevas, Pedro Pablo; Gironás León, Jorge Alfredo; Brand, I.; Branger, F.; Rodríguez, F.; Vargas, X.; Hitschfeld, N.; Muñoz Pardo, José Francisco; Vicuña, Sebastián; Mejía, A.; Jankowski, S.; CEDEUS (Chile)
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    Decomposition of 2D polygons and its effect in hydrological models
    (2019) Sanzana Cuevas, Pedro Pablo; Gironás León, Jorge Alfredo; Braud, I; Hitschfeld, N.; Branger, F.; Rodríguez, F.; Fuamba, M.; Romero, J.; Vargas, X.; Muñoz, J. F.; Vicuña, S.; Mejía, A.; CEDEUS (Chile)
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    Delfin plus plus : A Delaunay based algorithm for finding 3D polyhedral voids in galaxy surveys
    (2023) Guidotti, V.; Alonso, R.; Bravo, M.; Hitschfeld, N.; Marinello, G.; Hervias, C.; Campusano, L. E.
    Delfin++ (Delaunay Edge Void Finder) is a simple and time-efficient algorithm, with a single input variable, designed to find cosmological voids within a 3-dimensional distribution of galaxies by characterizing them as polyhedral regions from a Delaunay tessellation. Two density metrics are defined and used to search for density minima and construct polyhedra that represent the underdense zones. A density threshold is used to define the limit above which a galaxy will not be considered part of a void. This threshold is commonly defined as 0.2n over bar , where n over bar is the mean point density of the sample, whereas the values used in this work range from 0.2n over bar to 0.33n over bar . The algorithm is applied to artificial data, with different density contrasts, as well as to galaxy data from SDSS DR10. The detected voids are compared with voids that have been produced through the application of VIDE. Our algorithm detects roundish underdense regions in the galaxy samples, with differences and overlaps compared to the VIDE algorithm's results. Closer agreement is revealed when the edge length density metric is used over large galaxy samples, allowing for the detection of up to 90% of the largest VIDE voids. We measure ellipticities of Delfin++ detected voids and find that their distribution is shifted towards smaller values in comparison with VIDE's distribution, and with predictions from an analytical model. The voids found with Delfin++ are not intended to generate a catalog, but rather represent a proof of concept of a simpler algorithm or with fewer rules for further calibration and future production of a final catalog. Delfin++ performance tests suggest that enhanced characterization of voids can be achieved through (i) choice of other density threshold values, and (ii) early recognition and rejection of deformed polyhedra induced by missing data.& COPY; 2023 Elsevier B.V. All rights reserved.
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    Representation of the Drainage Network in Urban and Peri-urban Areas Using a 2D Polygonal Mesh Composed of Pseudo-convex Elements
    (2018) Sanzana, P.; Villaroel, S.; Braud, I.; Hitschfeld, N.; Gironas, J.; Branger, F.; Rodriguez, F.; Vargas, X.; Gomez, T.
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    Simulation of defects in aluminium castings using CAD models of flaws and real X-ray images
    (BRITISH INST NON-DESTRUCTIVE TESTING, 2005) Mery, D.; Hahn, D.; Hitschfeld, N.
    In order to evaluate the sensitivity of defect inspection systems, it is convenient to examine simulated data. This gives the possibility to tune the parameters of the inspection method and to test the performance of the system in cases where the detection is known to be difficult. In this paper, an interactive environment for the simulation of defects in radioscopic images of aluminium castings is presented. The approach simulates only the flaws and not the whole radioscopic image of the object under test. A manifold surface is used to model a flaw with complex geometry, which is projected and superimposed onto real radioscopic images of a homogeneous object according to the exponential attenuation law for X-rays. The new grey value of a pixel, where the 3D flaw is projected, depends only on four parameters: a) the grey value of the original X-ray image without flaw; b) the linear absorption coefficient of the examined material; c) the maximal thickness observable in the radioscopic image; and d) the length of the intersection of the 3D flaw with the modelled X-ray beam, that is projected into the pixel. The approach allows the user the simulation of complex flaws at any position of an aluminium casting. Simulation results of flaws like blow holes and cracks on X-ray images are shown and contrasted with real digital images with real flaws.