nach oben

2017 | Buch

Kapitel lesen Erstes Kapitel lesen

Mathematical Methods for Curves and Surfaces

9th International Conference, MMCS 2016, Tønsberg, Norway, June 23–28, 2016, Revised Selected Papers

herausgegeben von: Prof. Dr. Michael Floater, Prof. Tom Lyche, Marie-Laurence Mazure, Knut Mørken, Larry L. Schumaker

Verlag: Springer International Publishing

Buchreihe : Lecture Notes in Computer Science

Enthalten in: Springer Professional "Wirtschaft+Technik" , Springer Professional "Technik" , Springer Professional "Wirtschaft"

Einloggen, um Zugang zu erhalten

Über dieses Buch

This volume constitutes the thoroughly refereed post-conference proceedings of the 9th International Conference on Mathematical Methods for Curves and Surfaces, MMCS 2016, held in Tønsberg, Norway, in June 2016. The 17 revised full papers presented were carefully reviewed and selected from 115 submissions. The topics range from mathematical theory to industrial applications.

Inhaltsverzeichnis

Frontmatter

Computational Assessment of Curvatures and Principal Directions of Implicit Surfaces from 3D Scalar Data

Abstract

An implicit method based on high-order differentiation to determine the mean, Gaussian and principal curvatures of implicit surfaces from a three-dimensional scalar field is presented and assessed. The method also determines normal vectors and principal directions. Compared to explicit methods, the implicit approach shows robustness and improved accuracy to measure curvatures of implicit surfaces. This is evaluated on simple cases where curvature is known in closed-form. The method is applied to compute the curvatures of wrinkled flames on large triangular unstructured meshes (namely a 3D isosurface of temperature).

Eric Albin, Ronnie Knikker, Shihe Xin, Christian Oliver Paschereit, Yves D’Angelo

Coefficient–Based Spline Data Reduction by Hierarchical Spaces

Abstract

We present a data reduction scheme for efficient surface storage, by introducing a coefficient–based least squares spline operator that does not require any pointwise evaluation to approximate (in a lower dimension spline space) a given bivariate B–spline function. In order to define an accurate approximation of the target spline with a significant reduction of the space dimension, this operator is subsequently combined with the hierarchical spline framework to design an adaptive method that exploits the capabilities of truncated hierarchical B–splines (THB–splines). The resulting THB–spline simplification approach is validated by several numerical tests. The target B–spline surfaces include approximations of functions whose analytical expression is available, reconstructions of geographic data and parametric surfaces.

Cesare Bracco, Carlotta Giannelli, Alessandra Sestini

A Versatile Strategy for the Implementation of Adaptive Splines

Abstract

This paper presents an implementation framework for spline spaces over T-meshes (and their d-dimensional analogs). The aim is to share code between the implementations of several spline spaces. This is achieved by reducing evaluation to a generalized Bézier extraction.

The approach was tested by implementing hierarchical B-splines, truncated hierarchical B-splines, decoupled hierarchical B-splines (a novel variation presented here), truncated B-splines for partially nested refinement and hierarchical LR-splines.

Andrea Bressan, Dominik Mokriš

Machinability of Surfaces via Motion Analysis

Abstract

The machinability of a surface describes its ability to be machined and the factors which affect this. These are independent of any material properties or cutting parameters but instead reflect an ability to replicate a desired tool path motion with sufficient control of the material removal process. Without this control there is a potential for surface defects and costly finishing stages.

Five-axis CNC milling machines are commonly used for machining complex free-form shapes. The processes required to obtain CNC instructions for a machine tool, starting from a target surface, are presented. An overview is first given and later formalised with mathematical methods. Specifically, a moving cutting tool is characterised by a tool path motion. Interpreting the moving cutter in terms of moving machine axes provides a diagnostic tool for detecting machining errors.

Examination of two case studies reveals different types of errors, machine-dependent and machine-independent. The contribution of geometry to machine-independent errors is discussed and related back to the machinability of a surface.

Robert J. Cripps, Ben Cross, Glen Mullineux, Mat Hunt

Simplicial Complex Entropy

Abstract

We propose an entropy function for simplicial complices. Its value gives the expected cost of the optimal encoding of sequences of vertices of the complex, when any two vertices belonging to the same simplex are indistinguishable. We focus on the computational properties of the entropy function, showing that it can be computed efficiently. Several examples over complices consisting of hundreds of simplices show that the proposed entropy function can be used in the analysis of large sequences of simplicial complices that often appear in computational topology applications.

Stefan Dantchev, Ioannis Ivrissimtzis

Precise Construction of Micro-structures and Porous Geometry via Functional Composition

Abstract

We introduce a modeling constructor for micro-structures and porous geometry via curve-trivariate, surface-trivariate and trivariate-trivariate function (symbolic) compositions. By using 1-, 2- and 3-manifold based tiles and paving them multiple times inside the domain of a 3-manifold deforming trivariate function, smooth, precise and watertight, yet general, porous/micro-structure geometry might be constructed, via composition. The tiles are demonstrated to be either polygonal meshes, (a set of) Bézier or B-spline curves, (a set of) Bézier or B-spline (trimmed) surfaces, (a set of) Bézier or B-spline (trimmed) trivariates or any combination thereof, whereas the 3-manifold deforming function is either a Bézier or a B-spline trivariate.

We briefly lay down the theoretical foundations, only to demonstrate the power of this modeling constructor in practice, and also present a few 3D printed tangible examples. We then discuss these results and conclude with some future directions and limitations.

Gershon Elber

Partially Nested Hierarchical Refinement of Bivariate Tensor-Product Splines with Highest Order Smoothness

Abstract

The established construction of hierarchical B-splines starts from a given sequence of nested spline spaces. In this paper we generalize this approach to sequences formed by spaces that are only partially nested. This enables us to choose from a greater variety of refinement options while constructing the underlying grid. We identify assumptions that allow to define a hierarchical spline basis, to establish a truncation mechanism, and to derive a completeness result. Finally, we present an application to surface approximation that demonstrates the potential of the proposed generalization.

Nora Engleitner, Bert Jüttler, Urška Zore

Regression Analysis Using a Blending Type Spline Construction

Abstract

Regression analysis allows us to track the dynamics of change in measured data and to investigate their properties. A sufficiently good model allows us to predict the behavior of dependent variables with higher accuracy, and to propose a more precise data generation hypothesis.

By using polynomial approximation for big data sets with complex dependencies we get piecewise smooth functions. One way to obtain a smooth spline representation of an entire data set is to use local curves and to blend them using smooth basis functions. This construction allows the computation of derivatives at any point on the spline. Properties such as tangent, velocity, acceleration, curvature and torsion can be computed, which gives us the opportunity to exploit these data in the subsequent analysis.

We can adjust the accuracy of the approximation on the different segments of the data set by choosing a suitable knot vector. This article describes a new method for determining the number and location of the knot-points, based on changes in the Frenet frame.

We present a method of implementation using generalized expo-rational B-splines (GERBS) for regression problems (in two and three variables) and we evaluate the accuracy of the model using comparison of the residuals.

Tatiana Kravetc, Børre Bang, Rune Dalmo

On the Coupling of Decimation Operator with Subdivision Schemes for Multi-scale Analysis

Abstract

Subdivision schemes [5, 11] are powerful tools for the fast generation of refined sequences ultimately representing curves or surfaces. Coupled with decimation operators, they generate multi-scale transforms largely used in signal/image processing [1, 3] that generalize the multi-resolution analysis/wavelet framework [8]. The flexibility of subdivision schemes (a subdivision scheme can be non-stationary, non-homogeneous, position-dependent, interpolating, approximating, non-linear...) (e.g. [3]) is balanced, as a counterpart, by the fact that the construction of suitable consistent decimation operators is not direct and easy.

In this paper, we first propose a generic approach for the construction of decimation operators consistent with a given linear subdivision. A study of the so-called prediction error within the multi-scale framework is then performed and a condition on the subdivision mask to ensure a fast decay of this error is established. Finally, the cases of homogeneous Lagrange interpolatory subdivision, spline subdivision, subdivision related to Daubechies scaling functions (and wavelets) and some recently developed non stationary non interpolating schemes are revisited.

Zhiqing Kui, Jean Baccou, Jacques Liandrat

Translation Surfaces and Isotropic Transport Nets on Rational Minimal Surfaces

Abstract

We will deal with the translation surfaces which are the shapes generated by translating one curve along another one. We focus on the geometry of translation surfaces generated by two algebraic curves in space and study their properties, especially those useful for geometric modelling purposes. It is a classical result that each minimal surface may be obtained as a translation surface generated by an isotropic curve and its complex conjugate. Thus, we can study the minimal surfaces as special instances of translation surfaces. All the results about translation surfaces will be directly applied also to minimal surfaces. Finally, we present a construction of rational isotropic curves with a prescribed tangent field which leads to the description of all rational minimal surfaces. A close relation to surfaces with Pythagorean normals will be also discussed.

Jan Vršek, Miroslav Lávička

Towards Subdivision Surfaces C2 Everywhere

Abstract

The conditions for subdivision surfaces which are piecewise polynomial in the regular region to have continuity higher than C1 were identified by Reif [7]. The conditions are ugly and although schemes have been identified and implemented which satisfy them, those schemes have not proved satisfactory from other points of view. This paper explores what can be created using schemes which are not piecewise polynomial in the regular regions, and the picture looks much rosier. The key ideas are (i) use of quasi-interpolation (ii) local evaluation of coefficients in the irregular context. A new method for determining lower bounds on the Hölder continuity of the limit surface is also proposed.

Malcolm Sabin

Adaptivity with B-spline Elements

Abstract

This paper takes a stage further the work of Kraft [1] and of Grinspun et al. [2] who used subdivision formulations to show that finite element formulation can be expressed better in terms of the basis functions used to span the space, rather than in terms of the partitioning of the domain into elements. Adaptivity is achieved not by subpartitioning the domain, but by nesting of solution spaces. This paper shows how, with B-spline elements, their approach can be further simplified: a B-spline element of any degree and in any number of dimensions can be refined independently of every other within the basis. This completely avoids the linear dependence problem, and can also give slightly more focussed adaptivity, adding extra freedom only, and exactly, where it is needed, thus reducing the solution times.

Malcolm Sabin

Reconstructing Sparse Exponential Polynomials from Samples: Difference Operators, Stirling Numbers and Hermite Interpolation

Abstract

Prony’s method, in its various concrete algorithmic realizations, is concerned with the reconstruction of a sparse exponential sum from integer samples. In several variables, the reconstruction is based on finding the variety for a zero dimensional radical ideal. If one replaces the coefficients in the representation by polynomials, i.e., tries to recover sparse exponential polynomials, the zeros associated to the ideal have multiplicities attached to them. The precise relationship between the coefficients in the exponential polynomial and the multiplicity spaces are pointed out in this paper.

Tomas Sauer

Reparameterization and Adaptive Quadrature for the Isogeometric Discontinuous Galerkin Method

Abstract

We use the Poisson problem with Dirichlet boundary conditions to illustrate the complications that arise from using non-matching interface parameterizations within the framework of Isogeometric Analysis on a multi-patch domain, using discontinuous Galerkin (dG) techniques to couple terms across the interfaces. The dG-based discretization of a partial differential equation is based on a modified variational form, where one introduces additional terms that measure the discontinuity of the values and normal derivatives across the interfaces between patches. Without matching interface parameterizations, firstly, one needs to identify pairs of associated points on the common interface of the two patches for correctly evaluating the additional terms. We will use reparameterizations to perform this task. Secondly, suitable techniques for numerical integration are needed to evaluate the quantities that occur in the discretization with the required level of accuracy. We explore two possible approaches, which are based on subdivision and adaptive refinement, respectively.

Agnes Seiler, Bert Jüttler

Deconfliction and Surface Generation from Bathymetry Data Using LR B-splines

Abstract

A set of bathymetry point clouds acquired by different measurement techniques at different times, having different accuracy and varying patterns of points, are approximated by an LR B-spline surface. The aim is to represent the sea bottom with good accuracy and at the same time reduce the data size considerably. In this process the point clouds must be cleaned by selecting the “best” points for surface generation. This cleaning process is called deconfliction, and we use a rough approximation of the combined point clouds as a reference surface to select a consistent set of points. The reference surface is updated using only the selected points to create an accurate approximation. LR B-splines is the selected surface format due to its suitability for adaptive refinement and approximation, and its ability to represent local detail without a global increase in the data size of the surface.

Vibeke Skytt, Quillon Harpham, Tor Dokken, Heidi E. I. Dahl

Application of Longest Common Subsequence Algorithms to Meshing of Planar Domains with Quadrilaterals

Abstract

The problem of mesh matching is addressed in this work. For a given n-sided planar region bounded by one loop of n polylines we are selecting optimal quadrilateral mesh from existing catalogue of meshes. The formulation of matching between planar shape and quadrilateral mesh from the catalogue is based on the problem of finding longest common subsequence (LCS). Theoretical foundation of mesh matching method is provided. Suggested method represents a viable technique for selecting best mesh for planar region and stepping stone for further parametrization of the region.

Petra Surynková, Pavel Surynek

Order-Randomized Laplacian Mesh Smoothing

Abstract

In this paper we compare three variants of the graph Laplacian smoothing. The first is the standard synchronous implementation, corresponding to multiplication by the graph Laplacian matrix. The second is a voter process inspired asynchronous implementation, assuming that every vertex is equipped with an independent exponential clock. The third is in-between the first two, with the vertices updated according to a random permutation of them. We review some well-known results on spectral graph theory and on voter processes, and we show that while the convergence of the synchronous Laplacian is graph dependent and, generally, does not converge on bipartite graphs, the asynchronous converges with high probability on all graphs. The differences in the properties of these three approaches are illustrated with examples including both regular grids and irregular meshes.

Ying Yang, Holly Rushmeier, Ioannis Ivrissimtzis

Backmatter

Titel: Mathematical Methods for Curves and Surfaces
herausgegeben von: Prof. Dr. Michael Floater
Prof. Tom Lyche
Marie-Laurence Mazure
Knut Mørken
Larry L. Schumaker
Verlag: Springer International Publishing
Electronic ISBN: 978-3-319-67885-6
Print ISBN: 978-3-319-67884-9
DOI: https://doi.org/10.1007/978-3-319-67885-6