Progressive streaming and rendering of 3D terrain for cyber city visualization

Cyber city is a system that allows users to inquire about real world information quickly and conveniently on the internet. Terrain is one of the most important factors in the rendering of virtual scenes regarding cyber city visualization. For large-area and detailed representations of digital terrain models, rendering in real-time will be difficult because of the large data volume. It is also difficult to smoothly and efficiently broadcast virtual environments in large-scale web applications. To address these issues, this paper presents an efficient technique to progressively transmit and smoothly rebuild cyber city terrain models for internet-based geoinformatic applications. The full terrain was divided into regular tiles to stream adaptively. Different levels of detail of tiles were created and saved in the serve end and transmitted to clients according to different visualization conditions. The first task for progressive transmission was to transmit the base terrain data. Secondly, the LOD of each visible tile was determined based on viewing parameters in real time. Detail vectors describing changes of the LOD for each tile were then constructed and sent to the client to modify the developed mesh representation of the terrain. Algorithms for the decomposition and reconstruction of subdivision surfaces of tiles were also developed to update each tile as view-dependent parameters changed, so the clients could have smooth scene rendering. With this technique, users can reconstruct smooth approximations of the original scenes adaptively from a rather small amount of data received on the internet to increase the efficiency of terrain rendering in cyber city visualization.