Extensions to OpenGL for CAGD.

Many computer graphic API’s, including OpenGL, emphasize modeling with rectangular patches, which are especially useful in Computer Aided Geomeric Design (CAGD). However, not all shapes are rectangular; some are triangular or more complex. This paper extends the OpenGL library to support the modeling of triangular patches, Coons patches, and Box-splines patches. Compared with the triangular patch created from degenerate rectangular Bezier patch with the existing functions provided by OpenGL, the triangular Bezier patches can be used in certain design situations and allow designers to achieve high-quality results that are less CPU intense and require less storage space. The addition of Coons patches and Box splines to the OpenGL library also give it more functionality. Both patch types give CAGD users more flexibility in designing surfaces. A library for all three patch types was developed as an addition to OpenGL

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

Filling n-sided regions with G1 triangular Coons B-spline patches

International audienceFilling n-sided regions is an essential operation in shape and surface modeling. Positional and tangential continuities are highly required in designing and manufacturing. We propose a method for filling n-sided regions with untrimmed triangular Coons B-spline patches, preserving G1 continuity exactly. The algorithm first computes a central point, a central normal, the central, and the corner derivative vectors. Then the region is split into n triangular areas by connecting the central point to each corner of the boundary. These inner curves and all cross-boundary derivatives are computed fulfilling G1 compatibility conditions. And finally, the triangular patches are generated in the Coons B-spline form, one boundary of which is regressed to the central vertex. Neither positional nor tangential error is introduced by this method. And only one degree elevation is needed

The Construction of Optimized High-Order Surface Meshes by Energy-Minimization

Despite the increasing popularity of high-order methods in computational fluid dynamics, their application to practical problems still remains challenging. In order to exploit the advantages of high-order methods with geometrically complex computational domains, coarse curved meshes are necessary, i.e. high-order representations of the geometry. This dissertation presents a strategy for the generation of curved high-order surface meshes. The mesh generation method combines least-squares fitting with energy functionals, which approximate physical bending and stretching energies, in an incremental energy-minimizing fitting strategy. Since the energy weighting is reduced in each increment, the resulting surface representation features high accuracy. Nevertheless, the beneficial influence of the energy-minimization is retained. The presented method aims at enabling the utilization of the superior convergence properties of high-order methods by facilitating the construction of coarser meshes, while ensuring accuracy by allowing an arbitrary choice of geometric approximation order. Results show surface meshes of remarkable quality, even for very coarse meshes representing complex domains, e.g. blood vessels

Multisided generalisations of Gregory patches

We propose two generalisations of Gregory patches to faces of any valency by using generalised barycentric coordinates in combination with two kinds of multisided Bézier patches. Our first construction builds on S-patches to generalise triangular Gregory patches. The local construction of Chiyokura and Kimura providing G1 continuity between adjoining Bézier patches is generalised so that the novel Gregory S-patches of any valency can be smoothly joined to one another. Our second construction makes a minor adjustment to the generalised Bézier patch structure to allow for cross-boundary derivatives to be defined independently per side. We show that the corresponding blending functions have the inherent ability to blend ribbon data much like the rational blending functions of Gregory patches. Both constructions take as input a polygonal mesh with vertex normals and provide G1 surfaces interpolating the input vertices and normals. Due to the full locality of the methods, they are well suited for geometric modelling as well as computer graphics applications relying on hardware tessellation

HS-Patch: A New Hermite Smart Bicubic Patch Modification

Bicubic four-sided patches are widely used in computer graphics, CAD/CAM systems etc. Their flexibility is high and enables to compress a surface description before final rendering. However, computer graphics hardware supports only triangular meshes. Therefore, four-sided bicubic patches are approximated by a triangular mesh. The border curves of a bicubic patch are of degree 3, while diagonal and anti-diagonal curves are of degree 6. Therefore the resulting shape and texturing depend on the actual mapping, i.e. how the tessellation of a bicubic patch is made. The proposed new modification of the Hermite bicubic patch, the HS-patch, is a result of additional restriction put on the Hermite bicubic patch formulation - the diagonal and anti-diagonal curves are of degree 3. This requirement leads to a new Hermite based bicubic four-sided patch with 12 control points and another 4 control points, i.e. twist vectors, are computed from those 12 control points.Comment: Draft of the paper: NAUN Journal International Journal of Mathematics and Computers in Simulation, Vol.8, pp.292-299, ISSN: 1998-0159, 2014. arXiv admin note: substantial text overlap with arXiv:2212.11986, arXiv:2212.1187

Filling triangular holes by convex combination of surfaces

A surface generation method is presented based on convex combination of surfaces with rational weight functions. The three constituents and the resulting surface are defined over the same triangular domain. The constructed surface matches each component along one of its boundary curves with C0 or C1 continuity depending on the weight functions in the combination. The method can be applied in surface modelling for filling triangular holes

Mathematical description of curved domains via transfinite interpolation

Orientador: Philippe Remy Bernard DevlooDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Civil, Arquitetura e UrbanismoResumo: Este trabalho é dedicado ao desenvolvimento de uma metodologia específica de mapeamento curvo aplicável a qualquer tipo de elemento geométrico regular. Trata-se de uma generalização do modelo matemático de representação geométrica apresentado em 1967 por Steven Anson Coons, denominado "Bilinearly Blended Coons Patches", o qual ajusta uma superfície retangular em um contorno delimitado por quatro curvas arbitrárias. A generalização proposta permitirá a utilização deste tipo de interpolação geométrica em elementos de qualquer topologia, através de uma sistemática única e consistente.Abstract: In this work a methodology is developed for mathematical representation of curved domains, applicable to any type of finite element geometry. This methodology is a generalization of the mathematical model of a geometric representation presented in 1967 by Steven Anson Coons, called "Bilinearly Blended Coons Patches", which patch a rectangular surface in four arbitrary boundary curves. The proposed methodology is a kind of geometric transfinite interpolation applicable to elements of any topology, using a single and consistent systematic.MestradoEstruturasMestre em Engenharia Civi