【作者】 丰艳；

【导师】 陈一民；

【作者基本信息】 上海大学 ， 机械制造及其自动化， 2007， 博士

【摘要】 增强现实技术是在虚拟现实技术基础上发展起来的一项新技术，是对虚拟现实技术的一种新拓展。增强现实技术的关键是将计算机生成的三维虚拟物体同真实场景中的物体无逢融合，从而起到对真实世界信息补充和增强的作用。增强现实技术涉及到计算机科学中的诸多领域，早期的研究大多只是集中在三维注册问题上，即以提高跟踪、虚实配准过程的准确性为主要目标。近年来，随着研究的不断深入，如何提高增强现实系统画面的视觉一致性、提供更加逼真柔和的虚实融合界面，成为新的研究热点。增强现实技术的无缝融合问题，即一致性融合问题，主要包括几何一致性和光照一致性两个方面。本文以提高增强现实系统合成画面的真实感为目的，分别从几何一致性和光照一致性两个方面展开研究，取得了如下研究成果：1、提高增强现实系统的几何一致性，首先表现为虚实场景能够准确对位，这就要求系统必须能够以尽可能高的精度进行跟踪注册。准确的计算多坐标系之间的转换关系、准确的跟踪头盔视点的位姿，是跟踪注册中的两个重要环节。然而这两个环节中都无可避免的存在测量或计算上的误差。为此，首先本文对坐标系之间转换关系的计算问题进行扰动分析，并在此基础上给出了一种初始测量数据选取的依据，使得计算误差尽可能减小：其次针对磁力跟踪器存在的非线性误差，本文运用优化的神经网络对其进行非线性误差校正。2、随着系统的不断改进以及跟踪需要，我们又增加了双目视觉传感器进行跟踪。对于系统中的两套跟踪设备，如何实现两者的最佳协同工作模式，成为一个突出问题。对此，本文将模糊积分理论引入到该问题的讨论中，提出了基于模糊积分的信息融合算法：根据系统的特点设定模糊密度、选择评价因素、设计指标函数，最后建立了适合本文系统的融合模型，给出了一个双跟踪模式的智能融合跟踪系统，使整个增强现实环境的跟踪性能得到提高。3、真实场景与虚拟物体之间的相互遮挡，能够为用户的纵深距离感提供感知线索，同时能够丰富合成场景的三维层次效果、提高真实感。因此，实现虚实遮挡是增强现实系统几何一致性问题的另一重要内容。目前国内外解决该问题的主要思路，是在要求对真实环境已知的前提下，对真实场景事先建模或制作模板。这就需要大量繁琐的前期工作，而且真实环境的模型一旦建好，整个增强现实系统的应用环境也随即固定，因此系统的可移植性差，而且主要适用于解决刚体物等对象的遮挡问题。对此，本文提出了一种新的虚实遮挡实现算法，该算法避开了以往的惯用思路，而是基于open InVentor的运行机制，设计了动态EMO结点，并对虚拟场景进行分层次建模，同时运用复杂背景下的运动目标提取技术和Alpha通道技术，来实现虚实场景间的多层次相互遮挡。由于该算法不需要对真实环境事先建模，因此减少了大量的前期工作，而且提高了系统的通用性与可移植性。更重要的是，该算法对于非刚体物对象，也能很好的完成虚实间的相互遮挡。4、在光照一致性方面，本文提出了基于三维立体标志球的算法，对真实光照环境进行自动检测。双标志球均设计为具有近似理想的朗伯表面，通过标志球表面的图像亮度变化分析以及空间几何原理，建立真实光照的自动检测模型，从而获得真实环境的光照信息；然后，根据检测出的真实光照信息对虚拟场景进行二次光照处理，使虚、实场景具有基本一致的亮度效果。该算法避开了目前一些方法中需要对真实场景事先建模，或者离线进行光照估计的模式，算法简便、快速，可以实时的完成虚实场景的一致性光照渲染。更多还原

【Abstract】 Augmented reality (AR) is a new developing technology based on Virtual Reality(VR) but expand VR, and AR enhances the real world by superimposing computer generated information on top of it. AR relates to a good many fields of computer science. The early researches on AR mainly focus on Registered in 3-D, that is, its main object is to improve the tracking precision and the veracity of matching real and virtual scenes. Recently, with the development of research, it has become the new research hotspot that how to improve the visual consistency of synthetic images and how to produce more realistic synthetic interfaces.The problem of seamless fusion in augmented reality includes two aspects, the one is geometric consistency, and the other is illumination consistency. Aim at improving the third dimension of synthetic images in AR, this dissertation does some in-depth investigations on the above two aspects. The main contributions of the dissertation are as follows:1、Tracking and registration are two key technologies in AR, and their precision will directly affect the superposition of real and virtual scenes. However, the measurement error or calculation error always exist in the two processes, which calculate the transformation of coordinates and track the view point of user. So in the dissertation, we firstly give the perturbation analysis of calculating the transformation of coordinates, and then a selection criterion of initial metrical data is put forward, consequently to minish the calculation error. In addition, as for the nonlinear measurement error of magnetic tracker, we propose to rectify it using improved BP (Back Propagation) neural network in the dissertation.2、With the improvement of the whole system and considering the tracking range and precision, we subsequently added stereo-vision sensors. So in the dissertation, a data fusion model based on the notion of fuzzy integral is presented to combine the results of multiple tracking sensors. According to the application character in AR, the tracking range and the tracking error have been chosen to act as evaluation factors. A method for dynamically assigning weighting factors, using the comprehensive performance evaluation of individual sensors is also proposed. The fuzzy integral approach can release the user’s burden from tuning the fusion parameters.3、Realistic occlusion phenomenon is an important part of making AR environment convincing, as occlusion is well-known to be a strong depth cue. Mutual occlusion between real and virtual objects enhances the user’s impression that virtual objects truly exist in the real world. So it is another important factor of geometric consistency.An algorithm for realizing multilayer occlusion in AR is presented in the dissertation. We have designed a special scene graph tree comprised of some special nodes, that is, EMO nodes. According to the location of real moving object, different EMO node will be activated in real-time, consequently realizing the multilayer occlusion. Differing qualitatively from previous work in AR occlusion, our algorithm realizes multilayer occlusion, and its application domain involves indoor-field occluded objects, which are several meters distant from the viewer. Previous related work has focused on monolayer occlusion, and near-field occluded objects, which are within or just beyond arm’s reach.4、For a seamless AR system, apart from the geometric registration technique, the proper simulation of real lighting is another important factor. Such a factor determines the consistency of illumination between the virtual objects and the surrounding real objects. In the dissertation, two spheres with Lambert surface are introduced in the real scene. Through image analysis and analytical geometry of three dimensions, the illumination parameters of the real scene are estimated automatically. These parameters describe a point light source and ambient light. Using the estimated illumination parameters, the synthetic scene is relighted through inserting proper virtual light sources in the scene graph tree. This work explores an image-based analysis and post-illumination-processing approach to rapidly improve illumination consistency in AR system.更多还原