Subdivision for Generating Quadrics

Quadrics are of basic importance in Computer Graphics and Computer Aided Design. In this paper,we design a subdivision scheme based on the method suggested by G. Morin and J. Warren to generate conics and quadrics conveniently. Given the control polygon(p     

Method for fairing B-spline surfaces

A method of fairing tensor product B-spline surfaces is described. The technique is based on automatic repositioning of the surface control points by a constrained minimization algorithm. The objective function is based on a measure of the surface curvature, and the constraint is a measure of the distance between the original and the modified surfaces. Changes in surface shapedare analysed from illustrations of plane sections, contour plots of surface slope and Gaussian curvature, and colour plots of Gaussian curvature. These illustrations indicate that the present form of the technique is effective in some circumstances and suggest that improved implementations will produce more generally useful results.     

Artifact analysis on B-splines, box-splines and other surfaces defined by quadrilateral polyhedra

When using NURBS or subdivision surfaces as a design tool in engineering applications, designers face certain challenges. One of these is the presence of artifacts. An artifact is a feature of the surface that cannot be avoided by movement of control points by the designer. This implies that the surface contains spatial frequencies greater than one cycle per two control points. These are seen as ripples in the surface and are found in NURBS and subdivision surfaces and potentially in all surfaces specified in terms of polyhedrons of control points.Ideally, this difference between designer intent and what emerges as a surface should be eliminated. The first step to achieving this is by understanding and quantifying the artifact observed in the surface.We present methods for analysing the magnitude of artifacts in a surface defined by a quadrilateral control mesh. We use the subdivision process as a tool for analysis. Our results provide a measure of surface artifacts with respect to initial control point sampling for all B-Splines, quadrilateral box-spline surfaces and regular regions of subdivision surfaces. We use four subdivision schemes as working examples: the three box-spline subdivision schemes, Catmull-Clark (cubic B-spline), 4-3, 4-8; and Kobbelt?s interpolating scheme.     

一种对称非均匀细分曲面算法

为了得到能更好应用于CAD系统的细分曲面造型方法,提出一种基于B-样条的对称非均匀细分算法,其中的思想和均匀Lane-Riesenfeld节点插入算法相似。基于B-样条的节点插入算法,以Blossoming为工具,计算出细分后的新控制顶点。细分后得到的极限曲面由张量积样条曲面组成,在奇异点达到2C连续。与传统的细分曲面算法相比,该细分曲面算法具有良好的局部支撑性,大大降低了算法的复杂度,而且该算法是对称的,不用考虑定向问题。     

An Improving Subdivision Scheme for Curve Design

This paper extends the classical 4-point interpolatory subdivision scheme, and brings forward a new 4-point subdivision scheme with Three Parameters for Curve Design. We discuss the influence of three parameters to limit curve and realize the adjustment and control to it by choosing these three parameters appropriately, The sufficient conditions of the uniform convergence and continuity properties of the subdivision scheme are given.     

Non-uniform recursive Doo–Sabin surfaces

This paper presents a generalization of Catmull–Clark-variant Doo–Sabin surfaces and non-uniform biquadratic B-spline surfaces called Non-Uniform Recursive Doo–Sabin Surfaces (NURDSes). One step of NURDS refinement can be factored into one non-uniform linear subdivision step plus one dual step. Compared to the prior non-uniform Doo–Sabin surfaces (i.e., quadratic NURSSes), NURDSes are convergent for arbitrary n-sided faces. Closed form limit point rules, which are important for applications in adaptive rendering and NC machining, are given as well.     

Touch-enabled haptic modeling of deformable multi-resolution surfaces

Currently, interactive data exploration in virtual environments is mainly focused on vision-based and non-contact sensory channels such as visual/auditory displays. The lack of tactile sensation in virtual environments removes an important source of information to be delivered to the users. In this paper, we propose the touch-enabled haptic modeling of deformable multi-resolution surfaces in real time. The 6-DOF haptic manipulation is based on a dynamic model of Loop surfaces, where the dynamic parameters are computed easily without subdividing the control mesh recursively. A local deforming scheme is developed to approximate the solution of the dynamics equations, thus the order of the linear equations is reduced greatly. During each of the haptic interaction loop, the contact point is traced and reflected to the rendering of updated graphics and haptics. The sense of touch against the deforming surface is calculated according to the surface properties and the damping-spring force profile. Our haptic system supports the dynamic modeling of deformable Loop surfaces intuitively through the touch-enabled interactive manipulation.     

细分蒙皮曲面

对细分曲面在曲面造型中的应用进行了研究,并着重于蒙皮曲面造型技术．所提方法在传统的蒙皮曲面构造过程中引入细分方法,有效地避免了因截面曲线的相容性处理而产生的数据量激增的问题;最后生成的蒙皮曲面能够精确插值预先设计的截面曲线,并且可以在指定的截面曲线处产生折痕效果．     

Rational bicubic simple quadrilateral mesh surfaces

In free-form modeling a closed smooth piecewise surface is highly desirable when the smoothness across the boundaries of patches can be represented within the formulation. Closed, smooth, piecewise bicubic surfaces, defined on simple quadrilateral mesh. (SQM), may be defined as SQM surfaces. We have extended previous work on SQM surfaces and described the surface representation in rational form. The global constraint of the control parameters associated with each control vertex is relaxed. The new local shape-control parameters with their larger range of usability further enhance the power of this free-form surface design scheme. We have also provided more B-spline functions. A complete set of B-spline functions for various topologies of the SQM is now available. Examples demonstrate that editing of shapes for reasonably complex objects can be carried out on an SGI Personal Iris machine at an interactive rate.     

Extension of half-edges for the representation of multiresolution subdivision surfaces

We address in this paper the problem of the data structures used for the representation and the manipulation of multiresolution subdivision surfaces. The classically used data structures are based on quadtrees, straightforwardly derived from the nested hierarchy of faces generated by the subdivision schemes. Nevertheless, these structures have some drawbacks: specificity to the kind of mesh (triangle or quad); the time complexity of neighborhood queries is not optimal; topological cracks are created in the mesh in the adaptive subdivision case. We present in this paper a new topological model for encoding multiresolution subdivision surfaces. This model is an extension to the well-known half-edge data structure. It allows instant and efficient navigation at any resolution level of the mesh. Its generality allows the support of many subdivision schemes including primal and dual schemes. Moreover, subdividing the mesh adaptively does not create topological cracks in the mesh. The extension proposed here is formalized in the combinatorial maps framework. This allows us to give a very general formulation of our extension.     

Biorthogonal Loop-Subdivision Wavelets

We present a biorthogonal wavelet construction for Loop subdivision, based on the lifting scheme. Our wavelet transform uses scaling functions that are recursively defined by Loop subdivision for arbitrary manifold triangle meshes. We orthogonalize our wavelets with respect to local scaling functions. This way, the wavelet analysis computes locally a least squares fit when reducing the resolution and converting geometric detail into sparse wavelet coefficients. The contribution of our approach is local computation of both, wavelet analysis and synthesis in linear time. We provide numerical examples supporting the stability of our scheme.     

拟B样条离散曲面分层修改的研究

拟Ｂ样条离散曲面在曲面造型中是十分灵活的，但当对它进行局部修改时却存在一些不足，针对这一问题，本文提出了一种怕谓分层修改的方法，这一方法为设计者提供了新的有力的编辑工具。     

The definition and manufacture of compound curvature surfaces using G-surf

G-surf is a method for defining and machining the compound curvature surfaces encountered in many engineering applications. The surfaces are defined by orthogonal grids of B-spline space curves and machined with a cylindrical end-milling cutter inclined at predetermined angles to the surface normals. The approach proves to be very flexible and, as the cutter operates at a full and select cutting speed, gives an efficient means of material removal. Surface finish and cutter interference are both affected by cutter inclination to the surface normal and can be adjusted for optimum conditions.The interactive menu-driven package fits onto microcomputer installations and is suitable for small- to medium-size manufacturing companies.     

Generating subdivision surfaces from profile curves

The construction of freeform models has always been a challenging task. A popular approach is to edit a primitive object such that its projections conform to a set of given planar curves. This process is tedious and relies very much on the skill and experience of the designer in editing 3D shapes. This paper describes an intuitive approach for the modeling of freeform objects based on planar profile curves. A freeform surface defined by a set of orthogonal planar curves is created by blending a corresponding set of sweep surfaces. Each of the sweep surfaces is obtained by sweeping a planar curve about a computed axis. A Catmull-Clark subdivision surface interpolating a set of data points on the object surface is then constructed. Since the curve points lying on the computed axis of the sweep will become extraordinary vertices of the subdivision surface, a mesh refinement process is applied to adjust the mesh topology of the surface around the axis points. In order to maintain characteristic features of the surface defined with the planar curves, sharp features on the surface are located and are retained in the mesh refinement process. This provides an intuitive approach for constructing freeform objects with regular mesh topology using planar profile curves.     

Subdivision Schemes for Thin Plate Splines

Thin plate splines are a well known entity of geometric design. They are defined as the minimizer of a variational problem whose differential operators approximate a simple notion of bending energy. Therefore, thin plate splines approximate surfaces with minimal bending energy and they are widely considered as the standard "fair" surface model. Such surfaces are desired for many modeling and design applications.
Traditionally, the way to construct such surfaces is to solve the associated variational problem using finite elements or by using analytic solutions based on radial basis functions. This paper presents a novel approach for defining and computing thin plate splines using subdivision methods. We present two methods for the construction of thin plate splines based on subdivision: A globally supported subdivision scheme which exactly minimizes the energy functional as well as a family of strictly local subdivision schemes which only utilize a small, finite number of distinct subdivision rules and approximately solve the variational problem. A tradeoff between the accuracy of the approximation and the locality of the subdivision scheme is used to pick a particular member of this family of subdivision schemes.
Later, we show applications of these approximating subdivision schemes to scattered data interpolation and the design of fair surfaces. In particular we suggest an efficient methodology for finding control points for the local subdivision scheme that will lead to an interpolating limit surface and demonstrate how the schemes can be used for the effective and efficient design of fair surfaces.     

Smooth blending of subdivision surfaces

A technique for merging freeform objects modeled with subdivision surfaces is proposed. The method takes into consideration the possible distortion of the surfaces while the smoothness of the blending surface connecting the objects is maintained. A blend region between the given object surfaces is located. The topology of the surfaces in the vicinity of the blend region is refined and the boundary curves of the blend region are smoothed to reduce possible distortion in the blending surface. A blend curve between the two surfaces is used for connecting the given surfaces. Vertices on the blend curve are regular whereas extraordinary vertices are restricted to locate along the boundary of the blend region. Locations of the blend vertices are adjusted such that the curvature of the surfaces along the boundaries of the blend region is minimized. This ensures extraordinary vertices on the boundaries to lie on a relatively flat region, and hence, minimizes the distortion of the surfaces in the merging process.     

Good local behavior of offsets to rational regular algebraic surfaces

Local information on the shape of a regular surface is provided by the well-known notions in Differential Geometry of elliptic, parabolic and hyperbolic points. Here, we provide algorithms to check that, for a given distance, the offsetting process does not introduce relevant local changes in the shape of a surface, under the hypothesis that the surface is described by means of a rational, regular, real parametrization. Also, we provide algorithms for computing intervals of distances with this nice property.     

Sufficient conditions for draft angles on general B-spline surfaces

Many manufacturing processes, e.g. casting, forging, moulding, require that components must have a sufficient draft angle. Ensuring this when using general B-spline surfaces is a difficult task, often requiring iterative modeling. In this paper a theorem is presented that provides sufficient conditions to ensure draft angle on B-spline surfaces. The theorem is used to develop a simple algorithm that was used to add a draft angle to two surfaces.