Research On Adaptive LOD Methodology For Digital City

With the development of virtual technology and three-dimensional geospatial data collection technology, more and more cities began to build their own digital city. As the improved requirements of realism, digital city model not only has the mass of data, and has fine texture. This makes digital city model encountered the show effect and rendering time constraint each other in the visualization process. However the development of hardware and software is not sufficient to meet the real-time visualization requirements of such kind of complex models. Even the top-level computer can't real-time display all these data. The development of hardware technology makes a wide variety of hardware terminals emerging, the performance of these terminals are different each other, even if they belong to the same type. In all kinds of 3D real-time visualization applications, how to output satisfied image according to different user requirments and hardware/software environment, which is named adaptive visualization, has become an international research point and the academic front. For on-line applications of large scale digital city models, how to adaptively coordinate the rendering speed and quality according to factors such as data volume and hardware environment has been a critical issue of the applications of virtual geographic enviroments, CyberCity and digital earth.For the best visualization effect in a limited time the following two questions need to be resolved: one is Model simplification, the second is a limited time to choose which level of detail model rendering, that the draw time does not more than the limited time and can achieve the best visual effects. This paper study the simplification method based on edge collapse, gave an improved method base on edge collapse, it simplify the model and maintain the original characteristics of the model at the same time. Compute the rendering time and importance for each object in the digital city, and then choose the best draw program.Through the digital campus of Huazhong Normal University, the method in this paper is proved very good effective. In the end, the paper summarized all full text and presented profound research.