Streaming Transmission Of 3D Geometry Models

At the emergence of the World Wide Web, people ever dreamed about building a free-surfing three-dimensional (3D) virtual world. In this world, users could conveniently commune, deliberate, educate, entertain, even cooperate to design one sophisticated product or drill one difficult task by easy 3D graphical interface, while no longer constrained by physical space-time conditions. However, the vision has not come true until now. At present, the actual status can be illustrated as the following: on the one hand, peoples are more depending on the 3D graphics due that the graphical representation, especially the abstract and sophisticated things, is intuitional and easy to understand, on the other hand, the complexity of 3D geometrical data results in difficulty of network transmission, even out of user patience for waiting the data. The prime bottleneck preventing remote rending applications from extensive use is the antinomy between the network transmission and the geometrical data. In fact, the finite network bandwidth is more insufficient for 3D models, and the speed of current internet is far from the real-time transmitting requirement of large-scale 3D geometrical models. Consequently, the research on effective provision and real-time transmission of 3D geometrical information required by the user is one urgent affair, which can greatly promote the development of network graphics. This demand has not been fulfilled by software standards or their implementations, leaving a wide potential field for technical innovations.Currently, streaming is one of the most popular forms for network media transmission. As one burgeoning digital media, 3D geometrical model is more advantaged than traditional media, e.g., image and video, since it is initiative command rather than passive acceptance when ordering program of visualization. However, existed streaming media technique does not offer efficient transfers due to the complexity of 3D geometry. Thereby, the 3D streaming technologies are thoroughly investigated in the dissertation, whose main goal is to provide 3D contents in real time for users over a network connection, such that the interactivity and visual qualities of contents may match as closely as if they were stored locally, especially making interactions with 3D data possible without a complete download. Following the first established concept, streaming transmission of 3D geometry models, the key technique is studied. In the concrete, the researched themes include new pioneering designs and solutions for progressive compression, view-dependent and error-controlling streaming technologies for 3D models as well as technologies and applications for distribution frameworks, networking technologies for efficient and robust data communication mechanisms on current and next generation networks.Firstly, a progressive compression algorithm for triangle meshes is proposed, which can effectively reduce the storage size of triangle models by encoding it in a compact format and is suitable for network. The compression is driven by progressive degree-based topological encoding and a simple multi-granularity quantization in geometrical encoding, which allows making better of the dynamic range (different number bits in normal/tangential components) than with a fixed-bit representation. Experiments have shown that the presented method outperforms in the compression ratio. Particularlly, our proposed coder outperforms the original, proposed in SIGGRAPH 2001, in the rate-distortion curve and geometry coding efficiency, and the range of improvements is typically around 4%~20%.Secondly, a view-dependent mesh streaming algorithm has been proposed in this dissertation, which first attempts to effectively integrate the mesh compression with meaningful segmentation. The proposed algorithm first divides a mesh model into several meaningful components based on the minima rule from cognitive theory. The minima rule states that human perception usually divides a surface into parts along the concave discontinuity of the tangent plane. Our segmentation method extracts features, based on the minimal principal curvature value of surface vertices, to find candidate contours located in the valley. These open contours are prioritized to select the most salient one. Then, the selected open contour is automatically completed to form a loop around a specific part of the mesh by principal component analysis of its vertices. And then, the approach encodes each partition independently by a progressive half-edge collapse compression algorithm. The whole scene is organized by a new data structure, called hierarchical element tree, to progressively transmit and render selective meaningful parts in a view-dependent and random-access way. Therefore, the method can flexibly manipulate the resolution of different parts by elimination of insignificant details, and can reduce the required bandwidth by transmitting only high-resolution of visible parts while cutting out unusable details of invisible parts.Thirdly, two error-controlling mesh streaming approaches have been respectively adopted to reduce and prevent the error effects caused by package missing on network. The one is mesh segmentation scheme to depress channel error propagation. The typical 2D silhouette parsing short-cut rule is introduced to 3D mesh segmentation domain. Guided by the extended 3D short-cut rule theory, the method makes use of new geometrical and topological functions of skeleton to define initial cutting critical points by sweeping a given mesh perpendicular to every skeleton branch, and then employs salient contours with negative minimal principal curvature values to determine natural final boundary curves among parts. And sufficient experiments have been carried out on many meshes, and shown that our algorithm can provide more reasonable perceptual results in more robust way. The other is error detection through checks in the residual redundancy on the arithmetic coded data. An error resilient 3D mesh coding algorithm is developed, which employs Extended Multiple Quantization (EMQ) arithmetic coder method, inspired by the error-resilience mechanisms presented in Joint Photographic Experts Group (JPEG) 2000 image coding standards. With periodic arithmetic coder restarting and termination markers, the error resilient EMQ coder further divides bit stream into little independent parts and enables basic transmission error containment.Fourthly, the adaptive progressive remote rendering architecture (APRR), a new service-oriented architecture for progressive delivery and adaptive rendering of 3D contents, is proposed. APRR framework is designed by three common tiers, including client, middle server, and enterprise information system. The front two tiers, client and middle server, are implemented by famous "model-view-controller" design pattern. Especially, the middle service tier is comprised by loose-coupled and high-encapsulated functional modules, i.e., adaptive generation of 3D geometrical models with textures, hierarcial organization of 3D scene, and reaonable delivery mechanism of 3D modalities. The client tier is controled by a quality of service (QoS) controller for remote rendering of 3D contents, aiming at higher real-time performance just as rendering local 3D scenes. The prototype of APRR is developed and tested by a virtual military environment. The results have shown the advantages of APRR framework, which can greatly enrich the perception and performance of 3D objects in distributed applications. In a nutshell, APRR framework has many better properties, such as logical software architecture, easy flexibility and expansibility.The achievements of the dissertation have the significant academic values to enrich the computer network and computer graphics science and technology, and have the instructional meanings to develop the other projects, such as, networked Virtual Meseum, distributed collaborative Computer Aided Design, internet Geographic Information System, remote Visualization in Scientific Computing. This dissertation not only has made major progress in principle, but also has the important applications in the practical engineering projects. In fact, there are many economical/social benefits to be obtained remarkably.