计算机辅助草绘设计技术研究

计算机辅助草绘技术结合了计算机与纸笔草绘的优点，比较适合于概念设计，便于帮助设计师快速记录下头脑中产生的瞬时灵感，近年来一直成为许多专家学者争相研究的热点课题之一。该文从产品设计的领域出发简要介绍了计算机辅助草绘设计的研究现状。并从支持草绘的用户界面设计、低层草图处理、高层草图语义理解、三维草绘建模4个方面分析比较了计算机辅助草绘一些关键技术的研究方法，指出了下一步的研究重点。     

面向概念设计的实体草绘建模

提出了一种简单、快速、高效的基于草绘设计的概念模型创建方法.该方法模仿传统的纸笔草绘设计方式,允许用户自由地在笔式用户界面上勾画特征笔划,然后根据笔划的形状和位置关系采用基于特征的实体建模方法构造不同的扫描特征体素.在此基础上,采用了基于意图捕捉的特征添加及切削机制创建复杂的实体模型,给出了一些关键算法的实现过程.实验结果表明:该方法能够较好地应用到联机三维概念模型快速创建过程中.     

关于三维建模中草绘平面和参照平面的选择

在三维建模中,选择草绘平面和参照平面的正确与否决定了整个设计工作的成败。     

融合意图捕捉的笔式草绘特征建模

实现了一种基于笔式草绘特征建模方法.该方法模仿传统的纸笔草绘交互设计方式,利用意图捕捉机制揣测用户的设计意图,并采用基于特征的建模方法构造出三维实体概念模型.支持在模型表面上直接草绘截面和轨迹线,并通过特征切削或添加操作构造复杂物体模型;初步实现了基于手势的模型编辑操作.实验结果表明,该方法简单、高效,适合于快速表达不精确的概念模型.     

素描式草绘的三维花朵建模

三维花朵建模是虚拟现实中的重要部分,花瓣作为一种自由曲面,是整个建模的重点。提出了一种由非常自然的素描式草绘方式构造三维花朵模型的方法:从草绘图形中分析和提取信息,由这些信息计算出的横截面曲线来构造花瓣的曲面形状。通过草图绘制、笔划特征分析及识别、空间位置估计及曲面构造这几大步骤完成对花朵的三维建模。     

手绘草图的在线分段识别

提出了一种在线手绘草图快速分段识别方法。先对草绘笔划进行平滑预处理,以减少噪声干扰和冗余点的数目;然后利用草绘笔划的动静态特性,以及用户的草绘习惯等特性找出笔划的关键分段点,将笔划分为多个笔划子段;最后利用基于二次曲线的方法对笔划子段进行分段识别和特征参数计算,并通过构造面向对象的图形数据结构对识别出的几何图元进行重构。实例表明,该方法具有较好的识别能力和系统稳定性,能够应用于二维概念草图的快速表达,以及后续三维草绘建模的特征笔划智能识别过程中。     

协同设计中CAD模型局部变形加密方法

针对目前协同设计过程中信息安全风险,从提高CAD模型的安全性出发,提出一种基于CAD特征模型局部变形的敏感信息保护方法,通过对草绘参数进行变换,使模型几何形状发生变化,达到隐藏原模型信息的目的;然后提出了基于加密矩阵的草绘参数加密技术,采用一个加密矩阵作为秘钥对草绘中的控制点参数进行加密转换;进一步,为更好地控制加密后模型的变形趋势,引入几何计算中的自由变形方法,使用加密控制晶格对草绘进行加密,提出基于自由变形的草绘参数加密方法.最后通过对CAD零件模型进行实验,证明了文中方法的有效性..     

一种简单实用的草图编辑手势识别方法

联机草绘设计作为一种自然、高效的人机交互方式,继承了传统纸笔草绘设计的优点,弥补了现有CAD软件在处理模糊、不精确信息方面的不足,并日益受到人们的关注。针对联机草绘图形的编辑修改,设计出一套简单、快捷的编辑手势,并采用模式匹配的方法对其进行识别。实验结果表明,提出的方法具有较高的识别效果,加快了概念草图的设计过程。     

渐开线齿轮实体建模与模板研究

基于Pro/ENGINEER的参数化设计,是指先用一组参数定义零件的三维实体模型并确定参数关系,包含几何关系和拓扑关系,然后提供给设计人员进行零件三维造型使用,设计结果的修改由尺寸驱动.设计时不必考虑零件中几何元素的准确位置或数值,而是通过向图形添加适当的约束条件定义零件形状.零件的参数化模型就是带有参数名的草绘,用户通过编辑参数,零件几何模型的拓扑信息不变,而尺寸自动改变.每一个约束形成一个代数关系式,通过约束推理确定需要修改的尺寸参数,系统将自动检索此尺寸参数对应的数据结构,找出相关参数的方程组并计算出参数,驱动参数化模型形状的改变,从而形成新的零件三维实体模型.     

一种简单实用的草图编辑手势识别方法

联机草绘设计作为一种自然、高效的人机交互方式，继承了传统纸笔草绘设计的优点，弥补了现有CAD软件在处理模糊、不精确信息方面的不足，并日益受到人们的关注。针对联机草绘图形的编辑修改，设计出一套简单、快捷的编辑手势．并采用模式匹配的方法对其进行识别。实验结果表明，提出的方法具有较高的识别效果，加快了概念草图的设计过程。     

Investigating three-dimensional sketching for early conceptual design—Results from expert discussions and user studies

As immersive 3D user interfaces reach broader acceptance, their use as sketching media is attracting both commercial and academic interests. So far, little is known about user requirements and cognitive aspects of immersive 3D sketching. Also the latter's integration into the workflow of virtual product development is far from being solved.We present results from two focus group expert discussions, a comparative user study on immersive 3D sketching conducted among professional furniture designers and a qualitative content analysis of user statements. The results of the focus group discussions show a strong interest in using the three-dimensional (3D) space as a medium for conceptual design. Users expect it to provide new means for the sketching process, namely spatiality, one-to-one proportions, associations, and formability. Eight groups of functions required for 3D sketching were outlined during the discussions.The comparative study was intended to find and investigate advantages of immersive three-dimensional space and its additional degrees-of-freedom for creative/reflective externalization processes. We compared a 3D and a 2D baseline condition in the same technical environment, a VR-Cave system. In both conditions, no haptic feedback was provided and the 2D condition was not intended to simulate traditional 2D sketching (on paper). The results from our user study show that both the sketching process and the resulting sketches differ in the 2D and 3D condition, namely in terms of the perceived fluency of sketch creation, in terms of the perceived appropriateness for the task, and in terms of the perceived stimulation by the medium, the movement speed, the sketch sizes, the degree of detail, the functional aspects, and the usage time. In order to validate the results of the focus group discussions, we produced a questionnaire to check for the subjectively perceived advantages and disadvantages in both the 2D and 3D conditions. A qualitative content analysis of the user statements revealed that the biggest advantage of 3D sketching lies in the sketching process itself. In particular, the participants emphasized the system's ability to foster inspiration and to improve the recognition of spatiality and spatial thinking.We argue that both 2D and 3D sketching are relevant for early conceptual design. As we progress towards 3D sketching, new tangible interactive tools are needed, which account for the user's perceptual and cognitive abilities.     

Conceptual design, manufacturability evaluation and preliminary process planning using function-form relationships in stamped metal parts

A large number of design decisions are made during the conceptual design of a part. However, there are few representation and reasoning tools for decision support during conceptual design. The conceptual design stage is characterized by a lack of complete geometric information. Existing geometric modelers require complete geometric information, while a functional reasoning methodology using a <verb, noun > representation is typically too terse. In this paper, we present a new representation called sketching abstraction for conceptual design, using the function-form relations in a design. The functionally critical part of the geometry is presented using a set of functional features, while the rest of the geometry is abstracted as a set of linkages. Part functionality is correlated with the sketching abstraction using data structures called function-form matrices. The sketching abstraction is annotated using a set of primitives, and a set of grammar rules are used to extract canonical relationships between the functional features. The sketching abstraction can be used for extracting designs that are geometrically dissimilar but functionally similar, thus providing the designer with ideas for design alternatives. The sketching abstraction can also be used to carry out domain-dependent manufacturability evaluation checks. A further use of sketching abstractions is to initiate the development of a process plan for manufacturing. Sketching abstractions are related to the solid model of a part. Thus, this representation provides a link between pure functional and pure geometric representations. The domain of application is stamped metal parts. We present the part functionality and the features used in this domain. We also illustrate the use of sketching abstractions for conceptual design, manufacturability evaluation and preliminary process planning.     

手绘输入的三维建模和编辑技术

对当前基于手绘建模技术的研究现状进行分析,提出一个融合手绘识别与几何约束推理为一体的智能化建模体系,突出了概念建模过程中的逐步提纯、快速三维模型生成和编辑特性;针对手绘输入的二义性,提出对于多笔画连续输入的适应性逻辑推理模型以及自顶向下的约束树求解方法,不断组合历史信息,确定并创建出任意的三维模型.实验结果有效地显示和验证了此技术的高效性.     

Online Personalised Non‐photorealistic Rendering Technique for 3D Geometry from Incremental Sketching

This paper presents an online personalised non‐photorealistic rendering (NPR) technique for 3D models generated from interactively sketched input. This technique has been integrated into a sketch‐based modelling system. It lets users interact with computers by drawing naturally, without specifying the number, order, or direction of strokes. After sketches are interpreted as 3D objects, they can be rendered with personalised drawing styles so that the reconstructed 3D model can be presented in a sketchy style similar in appearance to what have been drawn for the 3D model. This technique captures the user's drawing style without using template or prior knowledge of the sketching style. The personalised rendering style can be applied to both visible and initially invisible geometry. The rendering strokes are intelligently selected from the input sketches and mapped to edges of the 3D object. In addition, non‐geometric information such as surface textures can be added to the recognised object in different sketching modes. This will integrate sketch‐based incremental 3D modelling and NPR into conceptual design.     

Conceptual design and modification of freeform surfaces using dual shape representations in augmented reality environments

This paper enables the rapid creation and modification of freeform surfaces inside an augmented reality environment, and focuses on methods for enabling increased flexibility during exploratory, conceptual industrial product design through three-dimensional (3D) sketch-based user input. Specifically, we address the role of multiple shape representations with varying uncertainty levels during 3D conceptual sketching, along with methods to transform between those representations. The main contributions of this work are: (1) the formulation of virtual shape data in multiple, concurrent representations (points and surfaces), and a regression method to transition fluidly back and forth between these representations during design, (2) methods for deforming and exploring the product shape using these multiple representations, and (3) representations of these forms such that designers can explore conceptual designs without the need for detailed surface operations such as trimming or continuity enforcement. Through incorporating these contributions, we introduce techniques that can be incorporated in future computer-aided conceptual design systems. These contributions are demonstrated for freeform surface design, with examples of computer mouse and car seat exterior surfaces.