Real-Time Web GIS Analysis Using WebGL

Parallel processing methods in Geographic Information Systems (GIS) are traditionally used to accelerate the calculation of large data volumes with sophisticated spatial algorithms. Such kinds of acceleration can also be applied to provide real-time GIS applications to improve the responsiveness of user interactions with the data. This paper presents a method to enable this approach for Web GIS applications. It uses the JavaScript 3D graphics API (WebGL) to perform client-side parallel real-time computations of 2D or 2.5D spatial raster algorithms on the graphics card. The potential of this approach is evaluated using an example implementation of a hillshade algorithm. Performance comparisons of parallel and sequential computations reveal acceleration factors between 25 and 100, mainly depending on mobile or desktop environments. DOI: 10.4018/ij3dim.2012070105 50 International Journal of 3-D Information Modeling, 1(3), 49-61, July-September 2012 Copyright © 2012, IGI Global. Copying or distributing in print or electronic forms without written permission of IGI Global is prohibited. Currently ongoing developments in web technology, like HTML5 (Hickson, 2012; WHATWG, 2012) and WebGL (Khronos Group, 2011a), offer great potential for the future development of more interactive, responsive, efficient and mobile Web GIS applications. This includes the usage of 2D, 3D and even temporal and animated content without the need of any third party plugins. The HTML5 specification introduces a new element type called canvas. For the first time, since the invention of the first widely used graphical web browser “Mosaic” in 1993 (Peterson, 2003), the canvas element enables web developers to not only present images, but manipulate images and also 3D scenes within the website using JavaScript. There are two different possibilities to manipulate graphics within a canvas element. One is the built in 2D drawing API for raster images and the other one is the WebGL API which can be used to create interactive 3D scenes with textured objects consisting of points, lines or triangles. Those two APIs are also referred to as “2d”or “webgl”-contexts of the canvas element. The WebGL API has a close connection to the graphics card. Its hardware is designed to rapidly project and rasterize 3D vector objects to the canvas plane on the screen. It can do such transformations very fast because it uses hundreds of specialized microprocessors in parallel. The ability to compute self-defined functions in parallel and output a raster graphic on a webpage as a result is the key property of the WebGL 3D-Technology, which in this paper will be exploited to outline the possibilities for extremely performing client side 2.5D Web GIS analysis using the example of a hillshade computation. The application of this approach opens up new perspectives on user interaction and interface design for the experience of in real-time responsive analysis results. A demonstration of the method can be evaluated on http://webgl.uni-hd.de/realtime-WebGIS. The following sections provide an overview on related work about parallel computation approaches of GIS analysis. A short introduction on the basics of 3D rendering and a detailed description how to use WebGL for the proposed method follows. Issues concerning the conversion of geospatial raster data to web compatible formats are addressed. An example hillshade algorithm is described and used to demonstrate and measure the performance of the approach. Furthermore some limitations of WebGL based spatial raster processing are discussed.