This paper presents a streaming technique for synthetic texture intensive 3D animation sequences. There is a short latency time while downloading the animation, until an initial fraction of the compressed data is read by the client. As the animation is played, the remainder of the data is streamed online seamlessly to the client. The technique exploits frame-to-frame coherence for transmitting geometric and texture streams. Instead of using the original textures of the model, the texture stream consists of view-dependent textures which are generated by rendering offline nearby views. These textures have a strong temporal coherency and can thus be well compressed. As a consequence, the bandwidth of the stream of the view-dependent textures is narrow enough to be transmitted together with the geometry stream over a low bandwidth network. These two streams maintain a small online cache of geometry and view-dependent textures from which the client renders the walkthrough sequence in real-time. The overall data transmitted over the network is an order of magnitude smaller than an MPEG postrendered sequence with an equivalent image quality.

Abstract—A distributed virtual walkthrough environment allows users connected to the geometry server to walk through a specific place of interest, without having to travel physically. This place of interest may be a virtual museum, virtual library or virtual university. There are two basic approaches to distribute the virtual environment from the geometry server to the clients, complete replication and on-demand transmission. Although the on-demand transmission approach saves waiting time and optimizes network usage, many technical issues need to be addressed in order for the system to be interactive. g�˜��‡—� � is a web-based distributed virtual walkthrough system developed based on the on-demand transmission approach. It achieves the necessary performance with a multiresolution caching mechanism. First, it reduces the model transmission and rendering times by employing a progressive multiresolution modeling technique. Second, it reduces the Internet response time by providing a caching and prefetching mechanism. Third, it allows a client to continue to operate, at least partially, when the Internet is disconnected. The caching mechanism of g�˜��‡—�� tries to maintain at least a minimum resolution of the object models in order to provide at least a coarse view of the objects to the viewer. All these features allow g�˜��‡—� � to provide sufficient interactivity to the user for virtual walkthrough over the Internet environment. In this paper, we demonstrate the design and implementation of g�˜��‡—��. We investigate the effectiveness of the multiresolution caching mechanism of g�˜��‡—� � in supporting virtual walkthrough applications in the Internet environment through numerous experiments, both on the simulation system and on the prototype system. Index Terms—Distributed virtual environments, model prefetching, multiresolution caching, multiresolution modeling, virtual walkthrough. I.

. Level of detail generation is important for managing geometric complexity of three-dimensional objects and virtual worlds. However, most algorithms that compute levels of detail do not deal with the special requirements of input data in VRML format. We report an algorithm called LODESTAR, based on octree quantization that robustly computes simplifications for objects in VRML. Keywords: VRML, polygonal object simplification, levels of detail, octree quantization 1. INTRODUCTION AND MOTIVATION Levels of detail (LODs) are approximations of an object with fewer geometric primitives, that are selected at run time to sustain interactive frame rates [1]. Reducing geometric complexity of geometric models is particularly important for VRML worlds for at least two good reasons: . While 3-D rendering systems are notoriously too slow, this is particularly painful for low cost devices such as personal computers that are most frequently used for VRML applications. . A single level of detail f...

Distributed virtual environments allow users at different geographical locations to share and interact within a common virtual environment via a local network or through the Internet. To deliver a good performance for such applications, we need to address several issues in different research disciplines. First, we must be able to model virtual objects effectively. The recently developed multi-resolution techniques for object modeling are of great value here, since they are capable of simplifying the object models and therefore reducing the time to render them. This may greatly reduce the demand for rendering performance on the client machines. Second, with the constraint of the limited bandwidth of the Internet, we need to reduce the response time by reducing the amount of data requested over the network. Caching of suitable object models of high affinity will reduce the amount of data requested over the network for a faster response time. Prefetching object models by predicting those ...

High-speed networks which guarantee a minimum quality-of-service (QoS) enable the development of interactive Web-systems. This paper introduces a new paradigm for interaction with complex virtual worlds on the web, which utilizes both the server and the client simultaneously. The client generates the new views by extrapolating a reference view based on the locally available data, including the model. The server transmits only the data necessary to prevent an accumulation of errors. The model-based view extrapolation method avoids the use of textures which are view-independent primitives and therefore too expensive to be used in interactive applications over the network.

In virtual environment systems, the ultimate goal is delivery of the highest-fidelity user experience possible. This paper describes a general-form framework for optimizing fidelity on a per-task basis. The virtual world database is priority-ordered; the ordering is dynamically recomputed based on display platform, virtual world state, and (possibly shifting) task objectives. Optimization is performed with the QUICK model, proposed herein, which integrates ratings of representational Quality, scene node Importance, and machine resource Cost. The approach has been implemented in a prototype display and distributed cache management system, which can be incorporated into most existing networked virtual reality applications. 1. Introduction The requirements of networked virtual environments strain the capacity of current technology in a number of directions: graphical rendering capability, processing speed, local storage, network capacity, and network latency. In this paper we introduce ...

For supporting real-time interaction in distributed virtual environments (DVEs), it is common to replicate virtual world data at clients from the server. For efficient replication, two schemes are used together in general-prioritized transfer of objects and a caching and prefetching technique. Existing caching and prefetching approaches for DVEs exploit spatial relationship based on distances between a user and objects. However, spatial relationship fails to determine which types of objects are more important to an individual user, not reflecting user's interests. We propose a scalable data management scheme using user-based caching and prefetching exploiting the object's access priority generated from spatial distance and individual user's interest in objects in DVEs. We also further improve the cache hit rate by incorporating user's navigation behavior into the spatial relationship between a user and the objects in the cache. By combining the interest score and popularity score of an object with the spatial relationship, we improve the performance of caching and prefetching since the interaction locality between the user and objects are reflected in addition to spatial locality. The simulation results show that the proposed scheme outperforms the hit rate of existing caching and prefetching by 10% on average when the cache size is set to basic cache size, the size of expected number of objects included in the user's viewing range.

Abstract—Interactive 3D content on the Internet has yet become popular due to its typically large volume and the limited network bandwidth. Progressive content transmission, or 3D streaming, thus is necessary for real-time content interactions. However, the heavy data and processing requirements of 3D streaming challenge the scalability of client-server-based delivery methods. We propose the use of peer-to-peer (P2P) networks for 3D streaming and argue that due to the non-linear access pattern of 3D content, P2P 3D streaming is a new class of applications apart from existing P2P media streaming. We also describe FLoD, the first P2P framework that allows clients in 3D virtual globe or virtual environment (VE) applications to obtain relevant data from other clients while minimizing server resource usage. To demonstrate how FLoD applies to real-world scenarios, a prototype system is built to adapt JPEG 2000 geometry imagebased streaming for the P2P delivery of 3D scenes. Experiments show that server-side bandwidth can be conserved with P2P streaming, while simulations indicate that P2P 3D streaming is fundamentally more scalable than client-server approaches. I.

This paper presents solutions for efficient rendering of SEAMS, for organizing the networking layer of a large-scale distributed virtual environment, and for sensible migration of objects and avatars from one world to another. It raises several design issues (both technical and social) which have to be addressed. Finally, results of our implementation are presented.

This thesis describes a web-based, responsive, zooming and panning visualization system for a full-featured geographic description of the United States. Current web-based map servers provide, from a visualization standpoint, little more than one static image per page, with hyperlinks for navigation; continuous zooming and panning requires locally stored data. Our primary contribution is a multi-threaded, scalable and responsive client-server architecture that responds to user requests as naturally and quickly as possible, regardless of network bandwidth reliability. This architecture can be generalized for use in other applications, including non-geographic ones. To this we add a scalable and exible user interface for navigation of multi-scale geographic data, with intuitive zooming and panning, pop-up feature labels, and a user controlled tree-hierarchy of windows. We build software tools and algorithms for translating the U.S. Census Bureau's TIGER data into a format designed for speedy database retrieval and network delivery, and for generalizing the data into multiple levels of detail. Because of anomalies in the TIGER data, this processing requires some human intervention. v vi Contents Acknowledgments iii Abstract v List of Figures xi List of Tables xiii 1