Terrain-VDR: Interactive Parallel Rendering System For Out-of-Core Terrain Dataset

Visualization of terrain is playing a key role in many applications, such as flight simulations, 3D games, geographic information system, etc. With the rapid development of the remote sense and satellite technology, people expect to investigate or view large terrain regions with finer precision;however, the interactive visualization of large terrain dataset is really a great challenge to us.In this paper, we propose an interactive parallel rendering system for Out-of-Core terrain dataset. The system is implemented in PC cluster and adopt retain mode based sort-first architecture. The rendering results are projected on a large display wall. The system includes a control client and fifteen rendering servers, which are connected by high speed Ethernet. The retain mode means that we store a copy of the whole terrain data in each rendering server, which avoids the frequency of transition of data in the network. The sort-first architecture is convenient for task partition between rendering server. The control client is responsible for the control and synchronization between the rendering servers. Besides, both geometry calibration and color calibration are performed in the multi-screen tile display and generate truly seamless display with high dynamic range.We present a novel view-dependent interactive terrain rendering algorithm. In order to exploit the capability of current GPU, the terrain geometry data is organized as quadtree, and each node of the quadtree is a triangle mesh, which is constructed and optimized off-line with high quality simplification and tristripping algorithms. Each node can be draw out using a single call. Exploiting the frame coherence, we construct the texture data as quadtree, and integrated with geometry quadtree, which handle the problem of large texture in real-time. In rendering time, the choosing of LOD is driven by screen space error. To keep the continuity of terrain surface mesh, the "skirt" technique is used to avoid T-crack, and geomorphing is used to remove the visual artifact when switching between different resolutions of LOD data. Furthermore, the complexity of the rendering scene is greatly reduced by view frustum culling.The delay caused by data exchange between main memory and secondary storage is the bottlenecks of real-time rendering out-of-core terrain dataset. Efficient out-of-core datamanagement is implemented in Terrain-VDR system, and the delay is greatly hidden. We used Scene Graph to organize terrain geometry data and texture data, which we called GST and TSG GST and TSG don't store the real data but only the description of data, and they are always keep in main memory. In real-time, the rendering server loads the requested terrain data into main memory from secondary storage, using the information of GST and TSG The loading algorithm is integrated with LOD which reduces the waiting time greatly. Moreover, we perform prefetch and unload operation, which improve the performance of real-time rendering further. The most important feature of our framework is that its performance is almost independent of the scale of the input data scale, regardless it is far beyond the internal memory.