Positive quartic, monotone quintic C2-spline interpolation in one and two dimensions

AbstractThis paper is concerned with shape-preserving interpolation of discrete data by polynomial splines. We show that positivity can be always preserved by quartic C2-splines and monotonicity by quintic C2-splines. This is proved for one-dimensional interpolation as well as for two-dimensional interpolation on rectangular grids

Smooth parametric surfaces and n-sided patches

The theory of 'geometric continuity' within the subject of CAGD is reviewed. In particular, we are concerned with how parametric surface patches for CAGD can be pieced together to form a smooth Ck surface. The theory is applied to the problem of filling an n-sided hole occurring within a smooth rectangular patch complex. A number of solutions to this problem are surveyed

Positivity Preserving Interpolation Using Rational Bicubic Spline

This paper discusses the positivity preserving interpolation for positive surfaces data by extending the C1 rational cubic spline interpolant of Karim and Kong to the bivariate cases. The partially blended rational bicubic spline has 12 parameters in the descriptions where 8 of them are free parameters. The sufficient conditions for the positivity are derived on every four boundary curves network on the rectangular patch. Numerical comparison with existing schemes also has been done in detail. Based on Root Mean Square Error (RMSE), our partially blended rational bicubic spline is on a par with the established methods

Visualization Of Curve And Surface Data Using Rational Cubic Ball Functions

This study considered the problem of shape preserving interpolation through regular data using rational cubic Ball which is an alternative scheme for rational Bézier functions. A rational Ball function with shape parameters is easy to implement because of its less degree terms at the end polynomial compared to rational Bézier functions. In order to understand the behavior of shape parameters (weights), we need to discuss shape control analysis which can be used to modify the shape of a curve, locally and globally. This issue has been discovered and brought to the study of conversion between Ball and Bézier curve

Shape-preserving algorithms for curve and surface design

PhD ThesisThis thesis investigates, develops and implements algorithms for shape- preserving curve and surface design that aim to reflect the shape characteristics of the underlying geometry by achieving a visually pleasing interpolant to a set of data points in one or two dimensions. All considered algorithms are local and useful in computer graphics applications. The thesis begins with an introduction to existing methods which attempt to solve the shape-preserving 1 curve interpolation problem using C cubic and quadratic splines. Next, a new generalized slope estimation method involving a parameter t, which is used to control the size of the estimated slope and, in turn, produces a more visually pleasing shape of the resulting curve, is proposed. Based on this slope generation formula, new automatic and interactive algorithms for constructing 1 shape-preserving curves from C quadratic and cubic splines are developed and demonstrated on a number of data sets. The results of these numerical experiments are also presented. Finally, a method suggested by Roulier which 1 generates C surfaces interpolating arbitrary sets of convex data on rectangular grids is considered in detail and modified to achieve more visually pleasing surfaces. Some numerical examples are given to demonstrate the performance of the method.Ministry of Education, Government of Pakista

Інтерполяція таблично-заданих функцій з використанням многочлена Фур'є

The methodology of interpolation of periodic table-given functions by the Fourier polynomial of the n-th order in arbitrarily located interpolation nodes has been developed. This methodology makes it possible to calculate the intermediate values of the function between nodal points, as well as to numerically differentiate them. Some features of interpolation of periodic Fourier polynomials of the n-th order are considered, the solution algorithm and mathematical formulation of the task of interpolation are given, the formalized notation of the task of interpolation is given, as well as the matrix notation of interpolation procedures for certain values of the argument in arbitrarily located interpolation nodes. There are many different ways of interpolating periodic table-given functions. It was found that the choice of the most suitable algorithm depends on how accurate the chosen method is, has the necessary stability and convergence, what are the costs of computer resources for its use, how smooth is the curve of interpolant, what is the number of data sets (argument values and corresponding functions values) it requires, etc. Algorithms for solving the task of interpolation of periodic of table-given functions by a Fourier polynomial of the 1st, 2nd, and 3rd orders are presented. The simplicity and clearness of this algorithm is one of its advantages, but it is inconvenient for its software implementation. The mathematical formulation of the interpolation task in terms of matrix algebra is presented, which is reduced to the calculation of the Fourier matrix using the values of nodal points known from the table, to the formation of the nodal column vector according to the function values specified in the table, and also to the solution of a linear system of algebraic equations, the root of which are the numerical coefficients of the Fourier polynomial of the n-th order. A method was developed for calculating the coefficients of the interpolant given by the Fourier polynomial of the n-th order, the essence of which is to calculate the product of the matrix which is inverted to the Fourier matrix, which is determined by the values of the nodal points of the table-given function, by the column vector, which contains the values of the interpolation nodes. Specific examples demonstrate the features of calculating the interpolant coefficients given by the Fourier polynomial of the 1st, 2nd, and 3rd orders, and for each of them, the interpolated value of the function at a given point is calculated. Calculations were performed in the Excel environment, which by analogy can be successfully implemented in any other computing environment.Розроблено методологію інтерполяції періодичних таблично-заданих функцій многочленом Фур'є n-го порядку в довільно розташованих вузлах інтерполяції, що дає можливість обчислювати їх проміжні значення між вузловими точками, а також чисельно їх диференціювати. Розглянуто деякі особливості інтерполяції періодичних многочленом Фур'є n-го порядку, наведено алгоритм розв'язання та математичне формулювання задачі інтерполяції, наведено її формалізований запис, а також матричний запис процедур інтерполяції для певних значень аргумента в довільно розташованих вузлах інтерполяції. Існує багато різних способів інтерполяції періодичних таблично-заданих функцій. З'ясовано, що вибір найпридатнішого алгоритму залежить від того, наскільки обраний метод є точним, має необхідну стійкість та збіжність, які затрати комп'ютерних ресурсів на його використання, наскільки гладкою є крива інтерполянти, яку кількість наборів даних (значень аргументів і відповідних значень функції) вона вимагає і т.д. Наведено алгоритми розв'язання задачі інтерполяції періодичних таблично-заданих функцій многочленом Фур'є 1-го, 2-го і 3-го порядків, простота й наочність якого є однією з його переваг, але він незручний для його програмної реалізації. Наведено математичне формулювання задачі інтерполяції у термінах матричної алгебри, яке зводиться до обчислення матриці Фур'є за відомими з таблиці значеннями вузлових точок, до формування вузлового вектора-стовпця за вказаними у таблиці значеннями функції, а також до розв'язання лінійної системи алгебричних рівнянь, коренем якої є числові коефіцієнти многочлена Фур'є n-го порядку. Розроблено метод розрахунку коефіцієнтів інтерполянти, заданої многочленом Фур'є n-го порядку, сутність якого полягає в обчисленні добутку матриці, оберненої до матриці Фур'є, яку визначають за значеннями вузлових точок таблично-заданої функції, на вектор-стовпець, який містить значення вузлів інтерполяції. На конкретних прикладах продемонстровано особливості розрахунку коефіцієнтів інтерполянт, заданих многочленом Фур'є 1-го, 2-го і 3-го порядків, а також для кожної з них обчислено інтерпольоване значення функції у заданій точці. Розрахунки виконано в середовищі Excel, які за аналогією можна успішно реалізувати й в будь-якому іншому обчислювальному середовищі

Arbitrary topology meshes in geometric design and vector graphics

Meshes are a powerful means to represent objects and shapes both in 2D and 3D, but the techniques based on meshes can only be used in certain regular settings and restrict their usage. Meshes with an arbitrary topology have many interesting applications in geometric design and (vector) graphics, and can give designers more freedom in designing complex objects. In the first part of the thesis we look at how these meshes can be used in computer aided design to represent objects that consist of multiple regular meshes that are constructed together. Then we extend the B-spline surface technique from the regular setting to work on extraordinary regions in meshes so that multisided B-spline patches are created. In addition, we show how to render multisided objects efficiently, through using the GPU and tessellation. In the second part of the thesis we look at how the gradient mesh vector graphics primitives can be combined with procedural noise functions to create expressive but sparsely defined vector graphic images. We also look at how the gradient mesh can be extended to arbitrary topology variants. Here, we compare existing work with two new formulations of a polygonal gradient mesh. Finally we show how we can turn any image into a vector graphics image in an efficient manner. This vectorisation process automatically extracts important image features and constructs a mesh around it. This automatic pipeline is very efficient and even facilitates interactive image vectorisation

Doctor of Philosophy

dissertationWhile boundary representations, such as nonuniform rational B-spline (NURBS) surfaces, have traditionally well served the needs of the modeling community, they have not seen widespread adoption among the wider engineering discipline. There is a common perception that NURBS are slow to evaluate and complex to implement. Whereas computer-aided design commonly deals with surfaces, the engineering community must deal with materials that have thickness. Traditional visualization techniques have avoided NURBS, and there has been little cross-talk between the rich spline approximation community and the larger engineering field. Recently there has been a strong desire to marry the modeling and analysis phases of the iterative design cycle, be it in car design, turbulent flow simulation around an airfoil, or lighting design. Research has demonstrated that employing a single representation throughout the cycle has key advantages. Furthermore, novel manufacturing techniques employing heterogeneous materials require the introduction of volumetric modeling representations. There is little question that fields such as scientific visualization and mechanical engineering could benefit from the powerful approximation properties of splines. In this dissertation, we remove several hurdles to the application of NURBS to problems in engineering and demonstrate how their unique properties can be leveraged to solve problems of interest

Geometrically exact theory for contact interactions

The intuitive understanding of contact bodies is based on the geometry and adjoining surfaces. A powerful approach to solve the contact problem is to take advantage of the geometry of an analyzed object and describe the problem in the best coordinate system. This book is a systematical analysis of geometrical situations leading to contact pairs: suface-to-surface, curve-to-surface, point-to-surface a.s.o. resultingin the corresponding computational algorithms to solve the contact problem

Parallel mesh adaptive techniques for complex flow simulation

Dynamic mesh adaptation on unstructured grids, by localised refinement and derefinement, is a very efficient tool for enhancing solution accuracy and optimise computational time. One of the major drawbacks however resides in the projection of the new nodes created, during the refinement process, onto the boundary surfaces. This can be addressed by the introduction of a library capable of handling geometric properties given by a CAD (Computer Aided Design) description. This is of particular interest also to enhance the adaptation module when the mesh is being smoothed, and hence moved, to then re-project it onto the surface of the exact geometry. However, the above procedure is not always possibly due to either faulty or too complex designs, which require a higher level of complexity in the CAD library. It is therefore paramount to have a built-in algorithm able to place the new nodes, belonging to the boundary, closer to the geometric definition of it. Such a procedure is proposed in this work, based on the idea of interpolating subdivision. In order to efficiently and effectively adapt a mesh to a solution field, the criteria used for the adaptation process needs to be as accurate as possible. Due to the nature of the solution, which is obtained by discretisation of a continuum model, numerical error is intrinsic in the calculation. A posteriori error estimation allows us to somewhat assess the accuracy by using the computed solution itself. In particular, an a posteriori error estimator based on the Zienkievicz Zhu model is introduced. This can be used in the adaptation procedure to refine the mesh in those areas where the local error exceeds a set tolerance, hence further increasing the accuracy of the solution in those regions during the next computational step. Variants of this error estimator have also been studied and implemented. One of the important aspects of this project is the fact that the algorithmic concepts are developed thinking parallel, i.e. the algorithms take into account the possibility of multiprocessor implementation. Indeed these concepts require complex programming if one tries to parallelise them, once they have been devised serially. Another important and innovative aspect of this work is the consistency of the algorithms with parallel processor execution