Research On Web-Based Visualization Technologies Of Massive 3D City Models

The city is an important living space that is closely related to human beings,and the virtual city three-dimensional scene is the multi-scale digital display of all the elements of the space.The combination of virtual city 3D scene and GIS forms a three-dimensional urban GIS,which will provide more direct auxiliary information for people's work,travel and life etc.It will also provide urban managers with all aspects of urban planning,construction and management decision-making information.The highly realistic 3D city model is an important part of 3D GIS.Large-scale three-dimensional city scene realistic display,smooth interaction and rapid query analysis are still the important topics in 3D GIS research.Real-time interactive visualization in large-scale three-dimensional urban models in the network environment is faced with many technical difficulties: network bandwidth bottlenecks,weak browser rendering performance,interactive display delays and lack of realism,which affect visual effects and interactive experiences.Based on the above problems,this paper deeply studies the key technology of visualization of 3D city model based on Web,and develops the 3D GIS prototype system under B/S architecture on the basis of Cesium open source project.The main work involved in this paper is as follows:1.In order to visualize the 3D models of large-scale artificial modeling,the 2D pyramid technology is deeply studied.Based on the 3D Tiles,a multi-level mixed-tile pyramid structure is proposed.It has good scalability and versatility,can meet the needs of the organization and management of complex three-dimensional scene data.Based on the organization structure of multi-level mixed pyramid tiles,a viewpoint-based scheduling method of mixed tile has been proposed to improve the fast retrieval of 3D model data and the rapid and efficient drawing of 3D scene,and reduce the drawing pressure of web client.2.In order to visualize the 3D models of large-scale oblique photogrammetry,the LOD technology of continuous surface model is deeply studied.The 3D simplification of oblique photography is simplified by the mesh simplification algorithm to optimize its rendering efficiency.This paper also proposes a method which is based on the set of vector surfaces to extract the target object from the photogrammetry 3D models,which realizes the data stratification and information query.3.For rapid fit and match of large-scale 3D model and terrain,a simple method of adaptively adjusting large-scale 3D model with terrain is proposed.The experimental results show that the matching effect of this method can meet the visual requirement.4.In order to visualize the multi-source hybrid data,this paper puts forward the solution of the combination of 3D photogrammetry Models and BIM models,so that the two are seamlessly integrated and complement each other to form a wide range of indoor and outdoor scene.