【作者】 周杰；

【导师】 罗杰波； 陈雪锦；

【作者基本信息】 中国科学技术大学 ， 信息与通信工程， 2018， 博士

【摘要】 关节式物体是指通过虚拟或者真实的关节将各个子部件联系到一起而形成一个整体的物体。其中,根据关节的静态与动态特性,可以将关节式物体分为静态关节式物体与动态关节式物体。关节式物体一直广泛地存在人们生活中的方方面面。在自然界中,树木的结构可以看作是由树枝组合而成的静态关节式物体,而动物的身体结构可以视为一种基于骨骼的动态关节式物体。在人造物体中,关节式物体更是多种多样,包括由零件组成的家具和机器,以及室内物体布局和大范围建筑群布局等等。随着计算机技术的不断发展,计算机的计算能力、数据采集技术、显示技术也在不断的提升。人们可以轻松地通过深度相机来采集和获取三维模型,也可以利用越来越方便地设计软件直接设计出丰富的关节式模型,而虚拟现实等技术也使得浏览和使用关节式模型变得越来越容易。在这样的背景下,不断扩大的应用场景也对关节式物体的分析和建模问题提出了越来越高的要求,使得该问题一直是计算机图形学中的一个重要研究方向。本文主要针对关节式物体这一研究对象,对其相关的几何结构分析与建模方法研究问题进行了分析和探讨。本文针对静态关节式物体和动态关节式物体两个方面,主要研究了积木式模型的构建和可折叠物体的几何结构设计两个问题,其中主要的工作内容和创新点如下:(1)积木式模型的构建问题。该问题是指对一个三维模型,如何用使用积木块来拼砌它。提出了一种自动化的积木拼砌系统,针对输入的建筑三维网格模型,生成与输入模型几何形状接近且符合美学标准的积木模型。提出了一种三维建筑模型上的视觉特征检测算法,可以提取一系列能够表达原模型几何形状和美学规则的视觉特征。在此之上,提出了一种将特征转化为积木子模块的算法。在最终的积木模型中,这些子模块则可以表达原有模型中对应的视觉特征等信息,使得拼装的积木模型与输入模型具有相似的几何形状,同时能够凸显原输入模型的美学特点。最终在完成拼砌设计之后,还能够给用户提供每一步的拼装指导。(2)可折叠物体的几何结构设计问题。该问题旨在生成一个可收缩展开的物体,在收缩状态下尽量紧凑、节省空间,同时可以展开成一个用户期望的形态,方便用户使用。提出了基于一组输入的子家具计算出一个可折叠家具设计方案的交互式计算系统。该问题首先需要选择子物体之间的连接拓扑关系,并在此之上计算每一个连接关系中子物体的相对位置和相对运动参数,才能最终生成一个可折叠家具。因此本文首先提出了一种高效的树空间选择算法。对于特定的树结构评价标准,能够从大量的树结构空间之中选择出潜在较优的结构,使得在有限的时间内能够完成对大量树空间的高质量搜索,降低了对整体树空间进行全局搜索的复杂性。在此之上,本文提出了针对可活动关节参数的交互设计算法。该方法基于连接结构的可运动空间,针对两两部件之间的运动空间进行了预计算,充分利用已知条件对搜索空间进行降维,提高了对于关节式物体的几何参数空间这一类复杂的离散连续混合空间的搜索效率。该算法结合了一种基于子树优化的模拟退火算法,使得系统能够在交互时间内,对于复杂的用户输入,给出较优的设计结果。由于该算法的特性,使得系统可以轻松地结合用户的交互操作,实时更新优化结果,便于用户得到期望的设计结果。更多还原

【Abstract】 A junction-based model is consisting of multiple components that are con-nected by junctions.Based on different types of junctions,the junction-based model could be divided into two types,as static junction-based model and mov-able junction-based model.There are many junction-based models in people’s everyday lives.In nature,the tree could be considered as static junction-based model consists of branches.The animal could be considered as movable junction-based model consists of skeleton.Among man-made objects,junction-based mod-els exist even more widely,including furniture and machine consists of basic parts,indoor layout consists of furniture and outdoor layout consists of buildings.In recent years,with the development of computer technology,the ability to acquire 3D model and the rendering technique has also been improved.People can capture 3D model with depth camera and design 3D model with interactive system more easily.The technique of virtual reality also makes browsing and using 3D model more conveniently.Based on these improvements,the demand for modeling and optimizing junction-based model has also increased.Therefore,junction-based model is becoming a more and more important research topic in computer graph-ics area.The main topic of this dissertation is the geometry analysis and modeling method of junction-based object.Targeting static junction-based model and movable junction-based model,this dissertation is focused on the problems of brick sculpture modeling and con-vertible object designing.The main work and innovations of this dissertation are listed as follows:(1)Brick sculpture modeling.Focusing on "Given any 3D body,how can it be built from bricks?",an automatic bricklize system is proposed.This system takes a 3D building model as input and can generate a vivid brick sculpture which is similar to the input model.We propose a visual feature detection method.The detected visual feature could represent the geometry shape and regularity of the input model.We then convert visual features into brick blocks.In the brick sculpture,these brick blocks could represent the repeating structures and regularity exists in the input model.In this way,the brick sculpture generated by this system could be vivid and express the characteristic of the input model.After the result is generated,an optimized building instruction could also be provided to the user for convenience.(2)Convertible object designing.In order to design a convertible object that can be packed into a compact shape for space-saving and can be expanded into a state for usage,an interactive system is proposed to take a set of furniture units as input and generate the convertible furniture.To solve this problem,the topology of the convertible furniture needs to be generated and the parameters of movable junctions need to be optimized.An efficient tree selection algorithm is proposed to generate the topology of the convertible furniture.This algorithm could select the potentially promising tree structures from a large tree space.By avoiding searching the entire tree space,this algorithm could largely reduce the complexity of optimization.The junction-dependent configuration space,which can be used repeatedly in different structure trees,allows our system to generate multiple suggestions for users at interactive speeds.The system also provides a set of interactive editing tools that allow the user to browse and edit the result and generate more desirable convertible furniture.更多还原