【作者】 管涛；

【导师】 王乘；

【作者基本信息】 华中科技大学 ， 空间信息科学与技术， 2008， 博士

【摘要】 增强现实(Augmented Reality简称AR)技术是近年来的一个研究热点,有着广泛的应用前景。它是对现实世界的补充,使得虚拟物体从感官上成为周围真实环境的组成部分。与传统的虚拟现实(Virtual Reality,简称VR)不同,增强现实只是实现对现实环境的补充而不是完全替代现实环境。增强现实技术增强了用户对现实世界的感知能力和与现实世界的交互能力。虚实配准(三维注册)是任何增强现实系统所必须解决的关键问题。它是指系统应该能够实时精确的计算摄像机相对于真实世界的位置和姿态,以便将虚拟场景正确的安置到它应所处的位置上。基于计算机视觉的三维注册方法以其精确性高、硬件成本低廉等特点已经引起越来越多研究人员的关注。本文针对当前基于计算机视觉的三维注册技术研究现状,吸取了计算机视觉、多视图几何、非线性优化理论的最新成果,围绕三维注册中的非定标配准方法、基于标识与平面自然特征相结合的注册以及基于多平面结构自然特征的虚实注册等技术内容展开研究与实践,目标旨在提高增强现实系统可用性的同时最大限度保证注册精度和系统实时性。本文的主要研究工作如下:(1)针对现有基于已知标识的三维注册系统中,要求用户必须事先确定摄像机内部参数的问题。设计一种基于实时定标策略的虚实配准方法,使得系统能够在运行过程中自动求取摄像机内参,提高了三维注册系统的精确性。(2)针对当前基于标识的开发平台在标识部分遮挡情况下无法完成三维注册问题,设计一种基于标识角点与全局单应性矩阵相结合的三维注册方法,减小帧间积累误差,增强了系统的健壮性与可用性。(3)设计一种综合利用标识与平面自然特征的三维注册技术,在标识全部被遮挡情况下利用标识周边区域的平面自然特征点来完成注册,可以直接改进现有基于标识的三维注册方法的健壮性和可用性。(4)分析当前各种基于自然特征的三维注册技术的优缺点,提出一种能够利用待注册场景中的多平面结构来完成注册的新方法。通过分析不同平面与视线的夹角不同以及视点与不同平面间的距离不同对最终计算结果的影响,提出一种有效的融合策略,可以较大幅度的减小抖动问题。更多还原

【Abstract】 Augmented Reality (AR) is a growing area in virtual reality research. An augmented reality system generates a composite view for the user. It is a combination of the real scene viewed by the user and a virtual scene generated by the computer that augments the scene with additional information. The augmented reality presented to the user enhances that person’s performance in and perception of the world. The ultimate goal is to create a system such that the user can not tell the difference between the real world and the virtual augmentation of it. To the user of this ultimate system it would appear that he is looking at a single real scene.Registration is one of the most pivotal problems currently limiting AR applications. It means that the virtual scenes generated by computers must be aligned with the real world seamlessly. Computer vision techniques have the potential to provide the accurate registration data needed by AR systems. The Vision-based methods do not require any special and expensive equipment except for common cameras and a personal computer. These kinds of methods take full advantage of scene features including man made markers, feature points, planes, and so on, to achieve registration between real and virtual scenes. In this paper, we especially focus on the computer vision based registration approaches. We mainly investigate the uncalibrate marker based method, marker and natural feature based method and multi-planar structures based method to improve the usability and robustness of the current AR systems.The main studies and achievements of thesis are listed as following:(1) Marker based uncalibrate registration methodWe propose a novel online dynamic calibration method to solve the problem that the intrinsic parameters of the camera can not be changed in the conventional marker based registration systems. Our method can calculate the intrinsic parameters according to the projections of the four corners in online stage and improves the usability and accuracy of the man made marker based AR systems to a large degree.(2) Registration under the circumstance of partially occlusion in marker based AR systemsWe present a new registration method based on global homography which can avoid the problem of occlusion and error accumulation in marker based Augmented Reality systems. We take following two steps to ensure the availability of our method. Firstly, a new affine invariant feature: edge-corner, is introduced to provide a robust and consistent matching primitives. Secondly, global Homography is used to calculate transformation matrix robustly by matching current and first frame to avoid error accumulation problem.(3) Registration using marker and planar structuresWe also propose a marker and planar texture based registration method. The initial registration matrix are obtained using known-size marker. The current registration matrix are calculated using homography between the current and previous frames when marker is occluded.Experiment results illuminate that our method improves the robustness and practicability of marker based registration systems particular under the circumstance of severe occlusion of man made markers.(4) Multi-Planar structures based registration for Augmented Reality systemsWe illustrate a novel registration method for augmented reality systems based on multi-planar structures and natural features tracking. The method can be divided into two stages: offline 3D reconstruction and online registration. In offline stage, the planes and world coordinate systems are established based on 3D reconstruction technique firstly. Secondly, we train the system by synthesizing a large number of views of matched features and by using PCA and K-means to generate a compact description of this view set. In online stage, we rely on this description to fulfill the task of feature matching based on nearest neighbor search method. With the obtained feature correspondences, we compute the homographies between the world planes and the current frame robustly using RANSAC and nonlinear least square method. Then, the registration matrix is synthesized using the above homographies and the transform matrices between the planes and world coordinate system obtained in offline stage. Our method cast off the requirement that the initial camera position should close to the reference images, while overcoming the problem of error accumulation. Some experiments have been carried out to demonstrate the validity of the proposed approach.更多还原