Study on Image-Based Real Time Walkthrough

在具有高度真实感的复杂虚拟环境中进行实时漫游一直是图形界的研究热点，其问题的关键之一在于如何有效地表达一个场景，并利用这种表达研究高质量的实时绘制算法。随着场景复杂度的不断提高，基于多边形的传统图形学已经很难实现一个复杂的"真实"虚拟环境的实时绘制。近年来新兴的基于图象的绘制技术和基于点的绘制技术采用新的绘制基元，取得了一些非常好的结果。本文试图在传统图形学以及现代发展技术之间寻求最佳的虚拟环境表达方式，并利用该方式实现"真实"虚拟环境的实时生成。本文提出一种从庞大参考图象数据中获取虚拟场景表达方式的方法。本文算法从一系列包含深度信息的参考图象出发，在场景三维模型未知的情况下，自动建立一个对复杂场景的点和多边形混合的表达方式，并在该表达方式下，实现对复杂场景的用户视点和视线方向不受限制的实时漫游。本文算法主要包含如下工作：本文提出了一种从庞大参考图象数据中获取虚拟场景表达方式的方法。该方法通过像素分类以及OBB技术将整个庞杂的输入数据重新组织为虚拟环境的有效表示；本文提出了一个点面混合的复杂场景表达方式，即以多边形的方式表达场景中大的平面物体，而以点的方式表达场景中形状复杂的物体。该表示充分利用传统图形学和现代图形学的新技术，以获取高效的虚拟场景表达方式；本文提出了一个基于Jacobi矩阵的采样密度比较算法，以删除参考图象间存在的大量冗余象素；本文提出了一个平面纹理提取方法。为弥补参考图象对场景表达不完备问题，本文给出了重建平面的空洞分析和预填补算法，在预处理阶段即对漫游时可能出现的空洞进行分析和高质量的填补；本文提出了一个针对基于点表达的物体的局部重建和重采样算法。通过该算法可以在物体表面上生成一系列尽量均匀分布的点，并在此基础上使用OBB树和法向量聚类的方式对重采样点进行有效的组织。通过这种组织方式，在漫游阶段可以采用一些有效措施来提高绘制效率，如基于聚类的Splat大小计算，选择合适的细节层次进行绘制等等；在点面混合表达的基础上，充分利用传统图形学和现代图形学的发展，本文实现了一个对复杂虚拟环境的用户视点和视线方向不受任何限制的实时漫游系统。Real time walkthrough in realistic complex virtual environments gradually becomes a hot topic in computer graphics, and it is increasingly in demands in various applications. One of its primary challenges is to find a way by which an environment could be well represented. With the increasing complexity of environment, traditional computer graphics based on polygons becomes hard to meet the requirement of real time rendering of a complex scene. On the other hand, two new techniques developed in recent years, image-based rendering and point-based rendering, come up to adopt new type of rendering primitives, and as a consequence, good results have been achieved in various applications. This thesis aims at embedding the two new techniques for real time walkthrough in a complex virtual scene. This thesis proposes an algorithm to build efficient representation for complex virtual environment from large set of reference images. Starting from multiple depth reference images, a hybrid representation of the complex scene will be automatically built up without knowledge of the original 3D models, and through this representation, a real time walkthrough in a large complex scene with no restriction to user's motion can be achieved. The main contributions of this thesis are: This thesis proposes an algorithm to build an efficient representation for large complex virtual environment from large set of reference images via pixel classification and OBB technique; This thesis proposes a hybrid representation of a complex scene by a combination of points and polygons. In more precise words in the approach, the large flat surfaces in the scene will be represented by textured polygons and the objects with high surface detail will be represented by points. The representation takes full advantages of traditional and cutting edge computer graphics techniques to achieve an efficient and packed representation for virtual environment; This thesis proposes a sampling rate comparison algorithm based on Jacobi matrix to eliminate redundant pixels among the reference images; This thesis proposes a texture reconstruction algorithm to reconstruct the corresponding textures of surfaces suitable for polygon-based representation. At the same time, holes which may appear in walkthrough will be analyzed and filled in the preprocessing stage; This thesis proposes a local reconstruction and resampling algorithm to generate a set of new samples which distribute more uniformly on surfaces and then they are organized by OBB-tree and normal vector clusters. Based on the efficient organization, several methods can be employed to improve rendering efficiency in walkthrough, such as cluster-based calculating of splat size, selecting proper detail level to render and so on; Based on the hybrid representation, this thesis proposes a real time walkthrough system for a large complex environment with no restriction to user's motion

基于Bin的高质量k—D树构建算法

中国计算机学会 中国自动化学会 中国图学学会 中国图象图形学学会 中国系统仿真学