Research On The Major Technologies Of 3D Visualization Of Massive Terrain Under Distributed Environment

As an important branch of computer graphics, terrain 3D visualization gradually involves with GIS, Virtual Reality, 3D games, and many other fields, and has been one of the research focuses by many scholars in recent years. In the past, research on terrain 3D visualization is mainly in a single computer. Accordingly, the technologies and algorithms which are used to increase the rendering speed of 3D terrain and improve the performance of terrain 3D visualization system are also based on the environment of. However, the existing technology can not effectively meet the demand of real-time and interaction of 3D visualization system because of the huge amount of terrain data under a single computer.Thus, considering the vigorous development of distributed parallel scheduling and services at present, the research on the major technologies of 3D visualization of massive terrain under distributed environment is carried out. Through the cooperatively parallel processing of many computers in a distributed environment, the scheduling and storage of massive terrain data could be performed effectively. 3D terrain should be simplified effectively according to vision principle and the own characteristics of scenes, and the real-time and interaction of 3D visualization of massive terrain is realized ultimately by reducing the number of graphics on real-time processing of the graphics system. Generally speaking, the main contents are as follows:1. According to the characteristics of massive terrain elevation data, a data organizational structure and storage model was studied, which is favor of rapid processing and scheduling of massive elevation data under distributed environment. Through establishing a Quadtree-based non-uniform resolution organization method which supports the efficient data block partition as well as the index mechanism for elevation data, the effective management and storage for the global terrain elevation data was accomplished.2. By studying real-time LoD algorithms for dynamic rendering of massive 3D terrain, a local adaptive optimization simplified terrain model (LaostModel) using Quadtree for massive terrain was established, which is used to solve the problem that whole terrain need to reprocess because of partial changes in some algorithms. The availability of the LaostModel algorithm was proved by system testing.3. According to the characteristics of massive image data and the organization methods of massive terrain elevation data, the data organizational structure and storage mode for massive image texture data was discussed, which should support the data scheduling and processing organization under distributed environment. And with it, a pyramid-pattern structure for global image texture data was realized. The other research content is texture mapping technology for massive image data.4. On the base of discussing parallel scheduling technology, database management technology, network technology, and so on, a data scheduling and processing model for massive terrain was expounded, which is suitable for distributed network architecture and supports cooperation of many computers within LAN. Also, dynamic scheduling strategy for terrain data is given, which is based on the above model and supports real-time rendering of massive 3D terrain.5. By using the models and methods introduced in this paper, a prototype system of global terrain 3D visualization within LAN was developed with Direct3D graphics components. Then, the performance testing for the prototype system was done for trying out the usability of the above research achievements.According to the above five aspects, the innovation in methods and techniques of this research were presented:i. The Quadtree-based multi-resolution organization model and index mechanism for massive terrain elevation and image texture data under distributed environment.Through studying data organizational structure and storage mode which support scheduling, processing and display of massive terrain data under distributed environment, a Quadtree-based multi-resolution organization model for massive terrain elevation and image texture data was established, with which the global terrain elevation data can be managed and stored effectively. It has been proved that the above model is suitable for network transmission and parallel processing for massive terrain data by the testing of prototype system.ii. The Quadtree-based local adaptive optimization simplified terrain algorithm for massive terrain (namely. LaostModel).According to organizational structure and storage mode of massive terrain elevation data, the LaostModel algorithm dynamically split or merges Quadtree data block according to viewpoint as well as the degree of roughness of local terrain, which also solves a lot of other problems, such as, the crack problem caused by different resolution grid mosaic of terrain, the problem that whole terrain need to reprocess because of partial changes. The different level terrain is display by real-timely adjusting the different Quadtree nodes in a data block with the LaostModel algorithm. Testing of prototype system shows that the model fits satisfactorily and offers a useful reference for further studying.iii. The data scheduling and processing model for massive terrain based on client / service mode in LAN.Bringing customers, services, and service management into full play and using a two-stage mode of communication as well as non-wait-asynchronous scheduling approach, the above model provides effective management to massive terrain data and ensures cooperative processing of data dispatch services and load balancing of network communications. Also, dynamic scheduling strategy based on the above model achieves the maximum sharing and utilizing of massive terrain data. Testing of prototype system had validated the reliability and efficiency of the model.With the development of the technologies, such as terrain data acquisition, networks communication, 3D visualization, the research on the major technologies of 3D visualization of massive terrain under distributed environment is expanding its application domains and is worthy to be intensively investigated further.