Search results for "computational geometry"
showing 9 items of 139 documents
Extension des méthodes de géométrie algorithmique aux structures fractales
2013
Defining shapes by iteration allows us to generate new structures with specific properties (roughness,lacunarity), which cannot be achieved with classic modelling.For developing an iterative modeller to design fractals described by a BCIFS, we developed a set oftools and algorithms that permits one to evaluate, to characterize and to analyse different geometricproperties (localisation, convex hull, volume, fractal dimension) of fractals. We identified properties ofstandard CAD operations (intersection, union, offset, . . . ) allowing us to approximate them for fractalsand also to optimize these approximation algorithms.In some cases, it is possible to construct a CIFS with generalised HUTCH…
Alternative method for binary shape alignment of non-symmetrical shapes based on minimal enclosing box
2012
Proposed is a novel method based on the minimal enclosing box (MEB) to determine the canonical orientation associated with a three-dimensional binary shape. It is suggested that, when the shape has no clear distinctive features and two or more of the eigenvalues are similar, this method is more suitable than the commonly used method based on principal component analysis (PCA). An experiment is performed with shapes of human livers by measuring the degree on which a prototypical image (atlas) matches to a new shape after alignment by PCA, minimal area projection (MAP), and MEB showing that in this case MEB outperforms the usual PCA-based alignment method and also the MAP method.
Metamagnetic Behavior in [M (tvp) (NCS)2] Coordination Polymers (M = Fe(II) and Co(II); tvp = 1,2-di-(4-pyridyl)-ethylene)
1999
Abstract We report the synthesis and magnetic properties of two new coordination polymers of formula [M(tvp)(NCS)2] (M = Fe(II) and Co(II)). The magnetic data reveal the occurrence of metamagnetic behavior. Switching from bulk antiferromagnetic to ferromagnetic behavior occurs for magnetic fields greater than 1300 G (Fe(II)) and 450 G (Co(II)) at temperatures lower than 4 K. Both compounds are isomorphous. A molecular structure is suggested in the light of the magnetic properties and precedent data on related systems.
An Optimized Architecture for CGA Operations and Its Application to a Simulated Robotic Arm
2022
Conformal geometric algebra (CGA) is a new geometric computation tool that is attracting growing attention in many research fields, such as computer graphics, robotics, and computer vision. Regarding the robotic applications, new approaches based on CGA have been proposed to efficiently solve problems as the inverse kinematics and grasping of a robotic arm. The hardware acceleration of CGA operations is required to meet real-time performance requirements in embedded robotic platforms. In this paper, we present a novel embedded coprocessor for accelerating CGA operations in robotic tasks. Two robotic algorithms, namely, inverse kinematics and grasping of a human-arm-like kinematics chain, ar…
Implementation and evaluation of medical imaging techniques based on conformal geometric algebra
2020
Medical imaging tasks, such as segmentation, 3D modeling, and registration of medical images, involve complex geometric problems, usually solved by standard linear algebra and matrix calculations. In the last few decades, conformal geometric algebra (CGA) has emerged as a new approach to geometric computing that offers a simple and efficient representation of geometric objects and transformations. However, the practical use of CGA-based methods for big data image processing in medical imaging requires fast and efficient implementations of CGA operations to meet both real-time processing constraints and accuracy requirements. The purpose of this study is to present a novel implementation of …
Approximation of pore space with ellipsoids: a comparison of a geometrical method with a statistical one.
2018
International audience; We work with tomographic images of pore space in soil. The images have large dimensions and so in order to speed-up biological simulations (as drainage or diffusion process in soil), we want to describe the pore space with a number of geometrical primitives significantly smaller than the number of voxels in pore space. In this paper, we use the curve skeleton of a volume to segment it into some regions. We describe the method to compute the curve skeleton and to segment it with a simple segment approximation. We approximate each obtained region with an ellipsoid. The set of final ellipsoids represents the geometry of pore space and will be used in future simulations.…
A Curvature Based Method for Blind Mesh Visual Quality Assessment Using a General Regression Neural Network
2016
International audience; No-reference quality assessment is a challenging issue due to the non-existence of any information related to the reference and the unknown distortion type. The main goal is to design a computational method to objectively predict the human perceived quality of a distorted mesh and deal with the practical situation when the reference is not available. In this work, we design a no reference method that relies on the general regression neural network (GRNN). Our network is trained using the mean curvature which is an important perceptual feature representing the visual aspect of a 3D mesh. Relatively to the human subjective scores, the trained network successfully asses…
A Complete, Exact and Efficient Implementation for Computing the Edge-Adjacency Graph of an Arrangement of Quadrics
2011
International audience; We present a complete, exact and efficient implementation to compute the edge-adjacency graph of an arrangement of quadrics, i.e. surfaces of algebraic degree 2. This is a major step towards the computation of the full 3D arrangement. We enhanced an implementation for an exact parameterization of the intersection curves of two quadrics, such that we can compute the exact parameter value for intersection points and from that the edge-adjacency graph of the arrangement. Our implementation is complete in the sense that it can handle all kinds of inputs including all degenerate ones, i.e. singularities or tangential intersection points. It is exact in that it always comp…
Sur la réductibilité des graphes de contraintes géométriques
2017
La modélisation géométrique par contraintes dont les applications intéressent des communautés issues de divers domaines tels l'ingénierie mécanique, la conception assistée par ordinateur, le calcul symbolique ou la chimie moléculaire est maintenant intégré dans les outils standards de modélisation. Dans cette discipline une forme géométrique est spécifiée par les relations que doivent vérifier les composants de cette forme au lieu de spécifier explicitement ces composants. Le but de la résolution est de déduire la forme répondant à toutes ces contraintes. Diverses méthodes ont été proposées pour résoudre ce problème. Nous nous intéresserons spécifiquement aux méthodes dites graphiques ou ba…