基于标识的特征造型原型系统的研究与实现

从特征造型软件开发的角度对参数化特征造型的一些关键技术进行了研究，并在ACIS几何平台上开发了一个参数化特征造型原型系统GDS。讨论了GDS的关键技术：基于标识的特征表示模型，标识子系统、统一二、三维约束的基于子图的草图设计及约束求解方法、基于约束依赖图的特征编辑算法等。     

一种适用于特征造型的参数化设计方法

本文提出了一种面向特征造型的参数化设计方法，该方法对三维几何约束在初始设计阶段采用高层表示，并基于面向特征造型的高层几何约束模型与约束传播实现尺寸驱动几何，从而能够有效地支持特征设计，初始设计。     

从工业界的角度看CAD技术的研究主题与发展方向

回顾了现有CAD系统所采用的主流、成熟技术,包括特征造型技术,基于历史的造型、参数化设计以及组件技术．从工业界的角度分析了当前CAD技术的若干研究主题,包括CAD与互联网、曲面造型、数据交换、从二维到三维、概念设计与早期设计等．并展望了未来的CAD系统,包括未来的计算环境、未来的机械CAD、未来的数据共享以及未来的零件造型技术。     

基于子图的草图设计和约束求解

提出了一种基于子图的拟序列化草图设计方法。基于标识的约束模型统一了二维、三维约束,使得每个几何元素对应唯一的标识,几何元素之间的约束关系表示为标识之间的约束,这些约束被分为结构约束和尺寸约束。提出了基于序列化设计过程的约束求解方法。实验表明,该技术可快速有效地进行参数化草图设计和特征编辑。     

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。     

特征模型直接操作技术的研究

目前的语义特征造型系统,由于约束求解的速度比较缓慢,还不能支持直接操作的特性。利用特征依赖图的数据模型来保存和维护特征的信息及其之间的依赖关系,并且提出了约束操作算法和特征操作算法,将特征的操作局限在模型的特定区域内。该方法最大限度地减少了所需要求解的约束数目,满足了直接操作过程中对约束求解速度的要求,从而实现了对特征的直接操作。     

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.     

一个标识子系统的设计与实现

特征造型的关键是合理地确定新旧模型拓扑元素之间的对应关系，文中提出一个基于特征的标识子系统，使得产品模型中每个拓扑元素都对应一个唯一的标识，标识匹配算法可以建立新旧模型拓扑元素之间的对应关系，标识子系统是作者开发的特征造型系统GDS的重要线成部分，为特征编辑、语义操作，二三维约束统一求解等奠定了基础。     

用于三维几何约束求解的分组重写方法

提出一种基于分组重写的解决三维几何约束的方法,原有的算法在解决大型系统几何约束求解时效率较低,系统开销较大,并且由于算法规则的局限性,使得很多复杂系统无法解决,包括三维几何约束问题。该方法提出了两种新的分组表示类型,拓展子集和放射子集,使得分组更加直观,准确,并有效地提高了求解效率,减小了开销,方法在三维领域更能发挥其作用,能够满足计算机辅助造型中集合造型的需求。     

三维服装CAD中几何约束表达及其求解技术研究

从人体及服装的特点出发，提出三维服装几何元素的概念．采用样条曲线作为基本几何元素，归纳出服装的三种约束关系，即共点、对称和自对称关系；成为约束关系形成的基础．以三种约束关系为基础，建立了面向服装的几何约束图，有效地表达了三维服装几何元素及其相互关系；实现了一种基于约束图的约束求解方法。从而完成了构造服装及对服装的交互参数化修改，文中给出了应用实例，并将参数化方法向高层次图素如样条曲线、曲面作了推广，成功地应用于以样条曲线为几何元素的参数化服装CAD系统中，运行效果良好。     

Hierarchical Geometric Constraint Model for Parametric Feature Based Modeling

A new geometric constraint model is described,which is hierarchical and suitable for parametric feature based modeling.In this model,different levels of geometric information are repesented to support various stages of a design process.An efficient approach to parametric feature based modeling is also presented,adopting the high level geometric constraint model.The low level geometric model such as B-reps can be derived automatically from the hig level geometric constraint model,enabling designers to perform their task of detailed design.     

Computer‐vision determination of 3‐D geometric parameters of LDL particles via cryogenic transmission electron microscopy

Abstract— Previous research has shown that the size of the LDL macromolecules can have an effect on cardiovascular health and that LDL macromolecules may be non‐spherical in shape. Some of these studies, however, used methods that are not conducive to automatic determination of the 3‐D parameters of the particles. In particular, the prior methods used for determination of geometric‐parameter determination were either centrifugal separations or manual determination of parameters from cryogenic transmission electron micrographs. An application of computer‐vision techniques to automatically determine the 3‐D parameters from cryogenic transmission electron microscopy (CTEM) images will be described. Correlation of computer‐generated geometric models to the orthonormal projection CTEM imagery were investigated to determine the applicability of finding the pertinent geometric parameters of the expected discoid shape of the LDL particles. The processing showed that the discoid shape can be verified using small‐angle rotations that are more amenable to the limitations of CTEM imaging.     

Editing 3D models on smart devices

This study proposes a 3D CAD system available on smart devices, which are now a part of everyday life and which are widely applied in various domains, such as education and robot industry. If an engineer has a new idea while traveling or on the move, or in the case of collaboration between more than two engineers, this 3D CAD system allows modeling to be performed in a rapid and simple manner on a smart device. This 3D CAD system uses the common multi-touch gestures associated with smart devices to keep the modeling operations simple and easy for users. However, it is difficult to input the precise geometric information to generate 3D CAD models by such gestures. It is also impractical to provide a full set of modeling operations on a smart device due to hardware limitations. For this reason, the system excludes several complicated modeling operations. This work provides a scheme to regenerate a parametric 3D model on a PC-based CAD system via a macro-parametrics approach by transferring the 3D model created on a smart device in an editable form to a PC-based CAD system. If fine editing is needed, the user can perform additional work on a PC after reconstruction. Through the developed system, it is possible to produce a 3D editable model swiftly and simply in the smart device environment, allowing for reduced design time while also facilitating collaboration. This paper discusses the first-ever system design of a 3D CAD system on a smart device, the selection of the modeling operations, the assignment of gestures to these operations, and use of operation modes. This is followed by an introduction of the implementation methods, and finally a demonstration of case studies using a prototype system with examples.     

Stabilizing 3D modeling with geometric constraints propagation

This paper proposes a technique for estimating piecewise planar models of objects from their images and geometric constraints. First, assuming a bounded noise in the localization of 2D points, the position of the 3D point is estimated as a polyhedron containing all the possible solutions of the triangulation. Then, given the topological structure of the 3D points cloud, geometric relationships among facets, such as coplanarity, parallelism, orthogonality, and angle equality, are automatically detected. A subset of them that is sufficient to stabilize the 3D model estimation is selected with a flow-network based algorithm. Finally, a feasible instance of the 3D model, i.e. one that satisfies the geometric constraints and whose 3D vertices lie within the associated polyhedral bounds, is computed by solving a Constraint Satisfaction Problem. The process accommodates uncertainty in a non-probabilistic fashion and thus provides rigorous results. Synthetic and real experiments illustrate the approach.     

Interactive Image‐Guided Modeling of Extruded Shapes

A recent trend in interactive modeling of 3D shapes from a single image is designing minimal interfaces, and accompanying algorithms, for modeling a specific class of objects. Expanding upon the range of shapes that existing minimal interfaces can model, we present an interactive image‐guided tool for modeling shapes made up of extruded parts. An extruded part is represented by extruding a closed planar curve, called base, in the direction orthogonal to the base. To model each extruded part, the user only needs to sketch the projected base shape in the image. The main technical contribution is a novel optimization‐based approach for recovering the 3D normal of the base of an extruded object by exploring both geometric regularity of the sketched curve and image contents. We developed a convenient interface for modeling multi‐part shapes and a method for optimizing the relative placement of the parts. Our tool is validated using synthetic data and tested on real‐world images.     

基于特征点加细的多分辨率人脸形变模型及人脸建模

提出基于特征点加细的原型三维人脸对应方法建立多分辨人脸形变模型,并根据该形变模型的特点使用多分辨模型匹配方法由单张正面人脸图像进行三维人脸建模。该方法以人脸模型上的眼、眉、口、鼻等主要几何特征为基准点标注基础网格,然后通过加细特征点网格完成原型人脸之间的对应,进而建立多分辨率的形变模型;根据形变模型的构造特点,把待匹配图像按照与模型相同方式进行加细,然后进行多分辨的人脸模型匹配。实验结果表明,新的对应算法可以有效地实现原型三维人脸之间的对应,能够克服传统的光流对应算法对应效果差,算法精度低的缺陷,提高形变模型的精度。新的匹配算法不仅能够加速模型的匹配速度,而且可提高模型匹配的效率和精度,缩短模型匹配的时间。     

以复形为基础的非流形造型与基于物理的造型相结合的物体表示

提出一个新的表示物体的框架。通过非流形造型与基于物理的造型相结合，从拓扑结构和几何信息两个方面扩大了模型的表示范围。以代数拓扑中的复形为基础的非流形造型的作用是生成物体的拓扑框架，既可以表示ＣＡＤ的物体，更适合表示具有复杂拓扑结构的自然物体。基于物理的造型的作用是在拓扑框架上生成最终的几何信息。二者的结合提供了一种新的几何造型手段。     

基于CV／CAD的三维物体几何建模

在虚拟现实等技术领域中,都涉及到由现实世界中的实际景物建立对应的计算机描述的虚拟景物的问题,为此提出了利用计算机视觉与CAD几何建模技术相结合的三维珠体建模途径,首先通过编码光栅方法获取三维物体的深度图象,并采用数学形态学的方法加以分割,然后利用代数曲面拟合手段对分割后的三维曲面片进行重建,并使用CAD几何建模工具由重建的曲面片构成物体的几何模型,该文给出了初步的实验结果,证明所提出的技术途径基本可行。     

交互的极线几何建模方法

讨论了一种基于图像的交互式几何建模方法，该方法利用手动方式标定模型的平行线、特征点，得到照相机参数，进而计算出模型的几何信息，并从图像中提取纹理，提出一种最优纹理选取算法，以确保拼接纹理的合理性，该算法主要应用于构造形状规则的模型，不需要知识照相机的内外参数，简便实用，实验结果表明，该方法在一定的场合下可以满足重建要求，重建出的三维模型具有照片真实感，并且能够实时漫游。     

基于物理的准D—NURBS造型方法

该文提出了基于物理的推Ｄ－ＮＵＲＢＳ的概念。ＮＵＲＢＳ由于既能够表示自由形状，又能够表示标准解析形状（即初等曲线曲面）而成为商业造型系统的标准。但直到目前，ＮＵＲＢＳ仍被看成是纯几何的设计工具，它要求我们手工调整控制顶点和相应权值来设计满足要求的形状。准Ｄ－ＮＵＲＢＳ则基于物理定律，将物体的质量分布，阻尼，内部变形能和其它物理特性与普通ＮＵＲＢＳ基结合，这使得我们不仅可以使用手工调整控制顶点和相应权值的传统方法，也可以施加模拟的外力和局部与全局几何约束而使设计形状依时间动态变形的方法来设计出满足要求的形状，通过物理变形的方法得到要求的形状使得设计更加直观，高效。同时，基于物理的准Ｄ－ＮＵＲＢＳ模型还用于柔性物体的运动、变形仿真。