附加自由曲面构造框架及其有效性维护的研究*

在对HUST-CAID(哈尔滨理工大学计算机辅助工业造型设计)系统进行研究的基础上,首先引入了自由曲面特征,然后结合HUST-CAID系统定义了自由曲面特征的分类和参数化,应用这种分类和参数化的方法创建了一个自由曲面特征,提出了一种基于FFDP配置的附加自由曲面特征的构造框架。此框架可以使自由曲面整体模型的构造完全参数化。最后建立了基于这个框架构造的自由曲面附加特征的有效性维护机制,从而达到对自由曲面附加特征进行有效性维护的目的。     

Numeric and curve parameters for freeform surface feature models

The success of feature modelling systems depends to a large extent on offering user-friendly ways for specifying and varying feature models. In this paper, several new facilities are introduced for this.Numeric and curve parameters are presented for specification and variation of freeform surface feature models. Several properties of the parameters can be defined, such as the direction of evaluation for a curve parameter. In addition to parameters present in features, other parameters can be added to a feature model, including intersection curves between features.To provide these facilities, a new three-level structure is introduced, which includes a partially evaluated model that can capture new generic model entities, including feature intersection curves. The work has been implemented in a prototype surface feature modelling system with functionality for feature class definition, feature model creation, and advanced feature model variation through the new types of parameters.     

自由曲面特征造型及其有效性维护的研究

对HUST-CAID（哈尔滨理工大学计算机辅助工业造型设计）系统研究的基础之上,引入自由曲面特征,运用自由曲面特征定义点构建几何形状轮廓曲线,实现特征参数化。其次,根据特征的分类和参数化,结合HUST-CAID系统的自身特点,完成特征类的定义,并在所构建的几何形状轮廓曲线的基础之上,使用扫掠法和蒙皮法技术构造出几何形状原型和最终的特征实例形状。最后,建立了一套自由曲面特征有效性维护机制。     

基于层次B样条的自由形状特征重用

借助层次B样条技术提出了一种自由形状特征的重用算法.首先利用低通滤波和泊松方程对源曲面上特征区域进行基面与细节特征的分离操作,求得基面与特征之间的偏移矢量场;然后利用平面参数化将偏移矢量场应用到目标曲面上完成特征重构;最后借助层次B样条技术优化重用结果.实验结果表明,该算法能够有效地完成自由形状特征的重用.     

自由特征模型参数化研究

为了更高效直观地对自由特征形状进行建模,对自由特征形体及自由特征定义点进行参数化,提出了一种通过封装参数和约束创建自由特征体特征的方法。在自由特征形状的定义中,建立数值参数和最终特征形状几何属性的映射关系。在轨迹线上提取特征定义点,在各点处建立横截面,对横截面进行蒙皮和扫掠运算,生成和基曲面无缝连接的自由形状体特征。     

自由特征模型约束求解研究*

在对自由特征模型参数化基础上,提出一种约束求解的新方法。该方法对自由特征形体定义点进行参数化,建立几何约束图,将约束问题分解为三角形约束和四面体约束两大类,分别进行求解,定义手向性规则,利用该规则将子问题组合为全局解。在自主开发的HUST-CAIDS（哈尔滨理工大学计算机辅助工业设计系统）中实现了本算法,并得到满足设计者需求的模型。     

密集标志点集的拓扑保持变换方法*

在对自由特征模型参数化基础上,提出一种约束求解的新方法。该方法对自由特征形体定义点进行参数化,建立几何约束图,将约束问题分解为三角形约束和四面体约束两大类,分别进行求解,定义手向性规则,利用该规则将子问题组合为全局解。在自主开发的HUST-CAIDS（哈尔滨理工大学计算机辅助工业设计系统）中实现了本算法,并得到满足设计者需求的模型。     

流线型结构特征造型方法及其在高速列车设计中的应用

提出了一种基于自由曲面的流线型结构特征造型方法,并将其应用于200km／h电动车组“先锋号”的流线型结构设计之中,流线型结构特征所描述的实体模型对自由曲面外形的变化具有自适应性,该方法便于流线型结构数据存取和修改,可在自由曲面外形和流线型结构各种参数多次修改的情况下自动生成流线型结构实体;大幅度地减少了人机交互时间,解决了高速列车流线型结构实体造型过程中设计周期过长的问题。     

基于弧长参数化的曲面W-M 分形插值

论文提出了一种以Weierstrass-Mandelbrot 分形（简称W-M 分形）与参数 曲面相合成来实现分形曲面的数字化建模的方法。指出了在参数曲面上合成W-M 分形以及 实施弧长参数化计算的必要性;论述了弧长参数化的具体算法,并用此方法实现了W-M 分 形与参数曲面的合成;在此基础上,提出了两向异性分形曲面的一种建模方法,实现了参数 曲面上进行两向异性W-M 分形的插值模拟。     

自由曲面特征模型中的数值和曲线参数*

成功的特征模型系统,在很大程度上取决于是否能给用户提供友好的方式来指定和改变特征模型,针对这一点,给出了两个新的功能：a）利用数值参数和曲线参数来指定和改变自由曲面特征模型;b）除了特征模型中现有的参数,其他参数可以添加到特征模型,包括特征之间的交叉曲线。为了提供这些功能,提出了一个新的三个层次的结构,最高层次为不可估计模型,最低层次为可评估的模型,中间层次为部分评估模型,后者链接最高层次的特征和最低层次的几何模型,并且也提供了最高层次和最低层次几何模型中的特征定义的交互。     

Parameterization and parametric design of mannequins

This paper presents a novel feature based parameterization approach of human bodies from the unorganized cloud points and the parametric design method for generating new models based on the parameterization. The parameterization consists of two phases. First, the semantic feature extraction technique is applied to construct the feature wireframe of a human body from laser scanned 3D unorganized points. Secondly, the symmetric detail mesh surface of the human body is modeled. Gregory patches are utilized to generate G¹ continuous mesh surface interpolating the curves on feature wireframe. After that, a voxel-based algorithm adds details on the smooth G¹ continuous surface by the cloud points. Finally, the mesh surface is adjusted to become symmetric. Compared to other template fitting based approaches, the parameterization approach introduced in this paper is more efficient. The parametric design approach synthesizes parameterized sample models to a new human body according to user input sizing dimensions. It is based on a numerical optimization process. The strategy of choosing samples for synthesis is also introduced. Human bodies according to a wide range of dimensions can be generated by our approach. Different from the mathematical interpolation function based human body synthesis methods, the models generated in our method have the approximation errors minimized. All mannequins constructed by our approach have consistent feature patches, which benefits the design automation of customized clothes around human bodies a lot.     

带自由曲面的三视图重建算法研究

针对蕴含自由曲面的三视图,提出了通过恢复边界线和轮廓线进而根据这些恢复 的空间曲线重建自由曲面的算法。首先分析并证明了自由曲面在三视图中的投影性质,从而提 出边界投影和轮廓投影的匹配算法。针对视图中存在的被打断的样条曲线,提出了分段样条曲 线的爬坡算法来解决此类曲线不能匹配的问题。然后基于投影匹配序列重建出自由曲面的边界 线,再由边界投影上的点和轮廓投影端点的对应关系重建出空间轮廓线。由轮廓线等参采样构 造截面线并和边界线一起蒙皮生成最终自由曲面。本文提出的算法扩展了工程图的重建域。     

自由曲面特征的定义与识别技术的研究

结合自主开发的HUST-CAID（哈尔滨理工大学计算机辅助工业造型设计）系统的特点,引入自由曲面特征,给出了自由曲面特征的参数化定义,并在此基础上对自由曲面特征识别进行研究,先是给出自由曲面特征识别的定义,接着提出了基于曲线的特征识别的算法。该方法将基于曲线的特征以二维参数的形式给出定义,使其能在二维平面上研究,通过重构特征的剖面模板库,从而利用目标特征与模板特征匹配实现了特征识别。     

一种三角网格模型的轮廓生成方法

从三维网格模型中提取轮廓信息是一个具有挑战性的过程。现有的方法一般是基于局部形状特征 分析,如曲面的曲率和相邻面法向之间的夹角,但其特性通常对模型中的局部特征变化敏感。为了解决这个问题, 提出一种基于三维形状几何近似的轮廓提取方法。利用完善的变分几何分割算法来得到一套完整的描述性特征曲 线,首先基于变分几何近似方法划分模型为若干分片;其次提取所有分片的内部特征曲线,并过滤较短的特征曲 线;然后将分片的边界曲线平滑化;最后合并分片边界曲线与特征曲线,并延伸曲线得到闭合的轮廓。该方法的 优点是：在几何近似的基础上结合特征提取方法,使轮廓能够体现三维形状的全局结构。通过在各类网格模型上 进行实验和比较表明,该方法在提取模型轮廓的正确性和完整性方面优于现有方法。     

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.     

基于特征线的三维服装部件参数化造型

基于特征线的服装三维造型方法有诸多优点,但是现有服装模型并不能很好地支持服装参数化设计.为此将参数化造型方法引入三维服装部件造型中,以得到参数化的服装部件.基于光顺人体模型,依据服装部件特点设计服装特征线,将特征线分为截面环和轮廓线,依次通过截面环和轮廓线的生成与调整、特征线综合调整和特征线添加约束3个步骤,得到服装特征线框架;并对该框架利用曲面插值方法得到服装曲面模型.实例结果表明,文中方法功能强大、方便灵活.     

Parameterization and reconstruction from 3D scattered points basedon neural network and PDE techniques

Reverse engineering ordinarily uses laser scanners since they can sample 3D data quickly and accurately relative to other systems. These laser scanner systems, however, yield an enormous amount of irregular and scattered digitized point data that requires intensive reconstruction processing. Reconstruction of freeform objects consists of two main stages: parameterization and surface fitting. Selection of an appropriate parameterization is essential for topology reconstruction as well as surface fitness. Current parameterization methods have topological problems that lead to undesired surface fitting results, such as noisy self-intersecting surfaces. Such problems are particularly common with concave shapes whose parametric grid is self-intersecting, resulting in a fitted surface that considerably twists and changes its original shape. In such cases, other parameterization approaches should be used in order to guarantee non-self-intersecting behavior. The parameterization method described in this paper is based on two stages: 2D initial parameterization; and 3D adaptive parameterization. Two methods were developed for the first stage: partial differential equation (PDE) parameterization and neural network self organizing maps (SOM) parameterization. The Gradient Descent Algorithm (GDA) and Random Surface Error Correction (RSEC), both of which are iterative surface fitting methods, were developed and implemented     

基于特征造型的自由曲面特征及约束求解的研究

在对HUST-CAID（哈尔滨理工大学计算机辅助工业造型设计）系统进行研究的基础上，首先引入了自由曲面特征。然后结合HUST—CAID系统定义了自由曲面特征的分类和参数化，同时系统为用户提供了一组适当的参数，使用户能够直观的设计任意曲面，而不必参与曲面的底层设计。当用户修改参数时，系统就会自动提供相应的反馈。为了求解出与约束一致的图形，还给出了一种新颖的原型驱动约束求解算法，并在HUST—CAID系统中进行了仿真实验，结果显示，此算法能够有效地简化约束求解和特征造型的过程。     

Progressive surface modelling scheme from unorganised curves

This paper presents a novel surface modelling scheme to construct a freeform surface progressively from unorganised curves representing the boundary and interior characteristic curves. The approach can construct a base surface model from four ordinary or composite boundary curves and support incremental surface updating from interior characteristic curves, some of which may not be on the final surface. The base surface is first constructed as a regular Coons surface and upon receiving an interior curve sketch, it is updated. With this progressive modelling scheme, a final surface with multiple sub-surfaces can be obtained from a set of unorganised curves and transferred to commercial surface modelling software for detailed modification. The approach has been tested with examples based on 3D motion sketches; it is capable of dealing with unorganised design curves for surface modelling in conceptual design. Its limitations have been discussed.