| 3D GIS can not only express the relationship between the plane and the vertical of spatial objects, but also can carry out three-dimensional space analysis and operation, give the person with real feelings. Therefore, the 3D visualization system based on desktop has been widely used in the construction of "digital city" and "smart city", which provides a strong technical support for the rapid development of our society. Currently, with the development of wireless Internet technology, mobile communication technology and a variety of mobile terminal technology, the traditional GIS is gradually moving to mobile GIS development. But these systems usually have higher hardware requirements, such as the speed of the computer, the physical storage space, the memory space, and so on, which can only be run on the strong performance of the notebook computer or desktop computer. In order to solve this problem, this paper aims to start with the data storage, network transmission, rendering mechanism and related technologies. Complete the design of the mobile 3D visualization prototype system based on Android, and realize the function of large scale 3D data fast browsing, spatial query analysis and so on.For the above-mentioned problem, this paper will focus on the following aspects to carry out research and analysis work and put forward the solution:(1) data organization and storage3D spatial data can be divided into terrain, image, model and other data. These data on the one hand to effectively enhance the sense of three-dimensional scene and the user’s experience, on the other hand, it also brings a lot of challenges to the operation of the mobile system. Adopt different strategies for different data, terrain, image data construction pyramid model of hierarchical block organization; model data using progressive mesh simplification algorithm is divided into basic model and node data in order to apply in the flow of network transmission. Finally all the data into the database, easy data query and management, so as to apply to the data network transmission and scheduling.(2) the transmission of 3D spatial dataThe existing data transmission strategy and the basic principles are analyzed and studied. At the current stage of network bandwidth, the network transmission of data is far less than the requirements of the system real-time rendering, resulting in a longer waiting time for users to reduce the system’s smooth experience. In this paper, based on progressive mesh streaming transmission technology of 3D data transmission, reduce time delay of data transmission and improve the system of browsing a smooth.(3) the visualization of 3D spatial dataFor the end of mobile 3D visualization prototype system, mobile devices have their own hardware computing ability is limited, screen resolution is fine, the contradiction between large amount of battery life time is not long and the 3D scene data, is the problem of 3D scene real-time rendering technology. In view of the above contradiction, this paper adopts strategy based on grid scheduling view distance, depending on the scene cut, data pre download cache, reduce data rendering, lighten the burden of the CPU rendering, so as to improve the fluency of the 3D visualization system of mobile.(4) Mobile 3D Visualization System Design and ImplementationAccording to the above proposed mechanisms and programs designed and implemented a large-scale terrain visualization systems, introduces the main function modules and visualization system, the performance of the system were experimentally compared and analyzed. |
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