VIRTUAL REALITY AND ITS APPLICATIONS IN CHINA: AN OVERVIEW <s> Fig. 1 The first CAVE system established in China <s> Abstract The networked workstation system is one of the commonly used Virtual Environment (VE) hardware platforms. In this paper we discuss distributed graphics support for implementation of VE systems and present an experimental environment called DGPSE+. It provides four kinds of consistency control methods: mutual exclusion, centralized controller, sequential ordering, and distributed lock. To meet the real-time requirement of VE systems, DGPSE+ contains a set of parallel graphics rendering algorithms with different computation requirement. A distributed stereoscopic graphics rendering is also included. It can find out idle or near idle workstations to execute the parallel algorithms. DGPSE+ has advantages such as multiple consistency control mechanisms and powerful graphics rendering support capability. <s> BIB001 </s> VIRTUAL REALITY AND ITS APPLICATIONS IN CHINA: AN OVERVIEW <s> Fig. 1 The first CAVE system established in China <s> Virtual Environment is a typical application of time-critical computing. To satisfy time-critical computing in distributed graphics environment, we may employ methods including hierarchical model representation, rendering algorithms with different computational complexity, and parallel processing. In this paper, we present a new time-critical computing model which uses the above three techniques.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only. <s> BIB002 </s> VIRTUAL REALITY AND ITS APPLICATIONS IN CHINA: AN OVERVIEW <s> Fig. 1 The first CAVE system established in China <s> This paper proposes a new preprocessing method for interactive rendering of complex polygonal virtual environments. The approach divides the space that observer can reach into many rectangular viewpoint regions. For each region, an outer rectangular volume (ORV) is established to surround it. By adaptively partitioning the boundary of the ORV together with the viewpoint region, all the rays that originate from the viewpoint region are divided into the beams whose potentially visible polygon number is less than a preset threshold. If a resultant beam is the smallest and intersects many potentially visible polygons, the beam is simplified as a fixed number of rays and the averaged color of the hit polygons is recorded. For other beams, their potentially visible sets (PVS) of polygons are stored respectively. During an interactive walkthrough, the visual information related to the current viewpoint is retrieved from the storage. The view volume clipping, visibility culling and detail simplification are efficiently supported by these stored data. The rendering time is independent of the scene complexity. <s> BIB003 </s> VIRTUAL REALITY AND ITS APPLICATIONS IN CHINA: AN OVERVIEW <s> Fig. 1 The first CAVE system established in China <s> A new nonlinear view interpolation algorithm is presented. Unlike the linear interpolation scheme, our method can exactly simulate the perspective viewing transformation during the walkthrough. To accelerate the view interpolation, the algorithm employs a binary subdivision scheme to optimize the decomposition of the source image so that the number of the resultant blocks is greatly reduced. Holes on the intermediate image are filled by two steps, namely enlarging the transferred blocks at the side adjacent to holes and retrieving the local image within the holes from the destination images by multiple-directional interpolation. Experimental results demonstrate our algorithm is much more accurate and efficient than the traditional one. <s> BIB004 </s> VIRTUAL REALITY AND ITS APPLICATIONS IN CHINA: AN OVERVIEW <s> Fig. 1 The first CAVE system established in China <s> An image\|based approach for virtual touring, which employs panoramas and picture\|based animation to compose a virtual environment, is presented. Two typical touring behaviors of players, namely, looking around and moving in one direction, are mimicked by using real\|time image processing engine. This approach has been implemented in Virtual \|Touring sightseeing system. In addition to panoramic views, the system provides picture\|based animation for moving forward to the next scene. The paper describes the architecture, authoring tools, and the interactive interface of prototype system. <s> BIB005
In Level of Detail (LoD)/multi-resolution direction, several new mesh simplification algorithms were proposed  , including a fast generation algorithm for progressive meshes  , a multiresolution modeling system, and new multi-resolution BSP tree  . (Fig. 2 shows a LoD example created with our algorithm). Static LoD and dynamic LoD methods are both explored. A new fast rendering algorithm incorporating both kinds has been developed. First, the polygonal models are simplified based on a user-specified error approximation, which is independent of viewpoint. Then the simplified models are used in a view-dependent real-time rendering algorithm. In real-time rendering, research works mainly focus on visibility pre-computing technique  BIB003 , nonlinear view interpolation technique BIB004 , and geometry and image based hybrid-rendering technique. The visibility pre-computing algorithm samples the environment in a 3D lattice. The potentially visible surfaces for each node are computed and stored, and the distant visible surfaces are simplified as textures. During walkthrough in a node, only the potentially visible surfaces and the textures attached to the node need to be rendered. The nonlinear view interpolation algorithm simulates precisely the perspective transformation during walkthrough. A binary decomposition scheme is proposed to reduce the number of sub-image blocks, which greatly improves the efficiency of the traditional view interpolation. In addition, some other research results have been obtained in the area of image-based modeling and rendering (IBMR) based on wavelets   , distributed virtual reality BIB001 , time-critical rendering BIB002 , and 3D acoustic rendering for virtual environments (VE)  . The Virtual ZJU (Virtual Zhejiang University) is a virtual touring system, which was implemented, based on IBMR. Fig. 3 is a snapshot of the images in this virtual touring system showing the gate of Yuquan Division, Zhejiang University. Some VR applications (medical treatment and surgery planning, architecture walkthroughs, and CAD/CAM) are being developed using the CAVE environment. VR research in this lab focuses on the IBMR method and its application. A project called Virtual Dunhuang Art Cave (DAC) was developed as a virtual navigation system  . The system provides new techniques and facilities for DAC presentation, investigation, and exploration. A demo view from navigation is shown in Fig. 4 . Another VR application is the VR TOURISM system BIB005 , which uses panoramas and picture-based animation to compose a virtual touring environment.