Study Of Adaptive Multi-Resolution Real-time Terrain 3D-Visualization System

Map is an important way to identify the features of environment and a foundational ingredient of any GIS system as well. Nowadays many of those who are engaged with geological survey and those who are focusing on developing GIS system aim at developing map from 2-dimention to 3-dimention. A reasonable way to fulfill this purpose is by terrain 3-D visualization in which we can employ the high calculation performance of a computer system and the splendid graphical ability of many graphic systems. In terrain 3-D visualization, the real-time visualization of large-scale terrain is always a big problem to be handled because of the large amount of data to be processed and the requirement of frame-rate.Based on a large-scale terrain real-time visualization system designed and implemented by the author, this paper firstly introduces some concepts and theories related to terrain model represented by triangulation. Then through comparison between several kinds of switching methods of level-of-detail, select CLOD (continuous level-of-detail) which is proper for real-time terrain visualization. Finally, choose the ROAM algorithm to implement CLOD. In this large-scale terrain real-time visualization system, designs an abstract data-structure software package that is the foundation of ROAM algorithm, and then implements algorithm details which the ROAM algorithm doesn't present. Using a 1025x1025 data sample, this system achieves a frame-rate of 20f/s on a Pentiuml.7G/256M personal computer.An important feature of real-time visualization system is that the user can interact with the system to control the display of the virtual scene. In this large-scale terrain real-time visualization system, designs and implements a view-controller that can simulate the operation of a real camera. It also can be used as parallel projector that keeps the coincidence of length in different direction and at different distance from the projector, thus can be used in a scientific visualization system. This view-controller is designed by object-oriented method, so it can be easily used in other systems.Besides the visualization function, this system also has some features such as interactive elevation querying, measuring the distance between two arbitrary points and the length of arbitrary polyline and measuring the perimeter and area of arbitrary polygonal region.UML(Unified Modeling Language) emerged in middle nineties last century, and in fact already become a international standard modeling language. It tends to be that all the software analysis and design should use UML as a tool in the future. In the process of developing this large-scale terrain real-time visualization system, the UML is used during the analysis and design phase, and the system is implemented by using VC++6.0 and openGL and can run on Windows operating systems including Windows98 and above.