BEYOND THE GOOGLE EARTH API—CESIUM, A PLUGIN-FREE, WEBGL-BASED VIRTUAL GLOBE

Google Earth can be viewed as a stand-alone application or embedded in a web page using the Google Earth application program interface (API). The API version offers many advantages but requires installation of a browser plugin which has been deprecated effective December 12, 2015. Plugins allow computers to run code that the browser application itself cannot read and are considered a security risk. They date back to Netscape and Mozilla describes them as legacy technology. The Google Earth plugin is already blocked by some browsers such as Chrome and Waterfox. Meanwhile, a WebGL-accelerated virtual globe technology called Cesium is being rapidly developed by the open source code community.

Cesium is a JavaScript library designed for HTML5 that draws 2D maps, 2.5D Columbus views, and 3D virtual globes without a browser plugin. It combines features familiar to users of Google Maps and Google Earth but also accesses tiled terrain imagery from Web Map Services (WMS), Tile Map Service (TMS), OpenStreetMaps, Bing, and Esri.

Cesium language (CZML), which is based on JavaScript Object Notation (JSON) enables time sequenced, data driven, graphical scenes to be created and shared without writing compiler code. Vector data are drawn with GeoJSON and TopoJSON, and 3D or 4D (animated) models can be added by converting COLLADA models to OpenGL Transmission Format (glTF). Most Keyhole Markup Language (KML) elements have been translated to CZML. There is support for virtual reality headsets such as Oculus Rift, augmented reality controllers such as Leap Motion, and the Google Web Toolkit (GWT). Most exciting for geoscientists are support for GPS tracks, 4D chloropleth maps, and a “ground-push” feature that allows sub-surface browsing. A number of geoscience projects are porting from the Google Earth API and NASA World Wind to Cesium, notably NASA iSat and Vesta Trek, and GPlates Web Portal. New applications are developed in a live, JavaScript/HTML/CSS editor called Cesium Sandcastle.