3D geographic scenes visualization based on WebGL

Abstract

With the fast development of the Internet, the lightweight 3-dimension (3D) geographic scenes visualization system is expected to play more important roles in web-based GIS. Finding an effective solution to render 3D geospatial data has great significance in Cartography and Geographic Information Systems. The emergence of HTML5, as well as WebGL (Web Graphics Library), provides a new approach for 3D WebGIS. WebGL is a JavaScript API for rendering 3D graphics within compatible web browsers. Other plugins are no longer required for displaying 3D objects. WebGL is regarded as a part of new generation web standards and is completely integrated into most popular browsers. It allows GPU accelerated usage of physics and image processing. WebGL elements can be mixed with other HTML elements and composited with other parts of the page or page background. This paper discusses the design and implementation of a digital city roaming system based on WebGL technology. Users can make cartographic analysis, destination query, data query and map mark with the system in browsers. All 3D models in the scene are converted to glTF (GL Transmission Format), and can be used to load 3D scenes and models. For the complex scenes, this system only downloads the scene data within the current view using visibility culling techniques, then joins these data into the rendering queues. At the same time, the data request task is managed in queue by the management layer using prefetching strategy. On the client-side, a method is proposed to deal with occlusion culling based on the parameters of current scene, geometry shape and positional relation. The client-side removes the occluded model data from memory, while the remaining visible data is passed to the GPU rendering pipeline. Then the client-side renders the scene in browser according to the parameters of these glTF files. The experiment result shows that this system can smoothly render the city 3D scene in the browser without any plugins. The city roaming system based on WebGL shows a good interactive experience of 3D visualization for users. The paper provides a very effective and promising method for establishing 3D WebGIS realization.