The effectiveness of a computer application depends on, among other things, an efficient user interface. In order to visualize subsurface geologic phenomena using the Google Earth™ application, we initially employed the built-in Google Earth time slider. Dragging the slider's right thumb elevated a COLLADA model that initially loads at a subsurface altitude. However, the double-thumb feature of the time slide caused users some difficulties. It is not possible to turn off this feature when not required, so it can be misleading to users. Because of this and because of the need for more control, we transitioned from the stand-alone Google Earth application to the web-based Google Earth plug-in. To overcome some of the limitation for the existing user interface, such as the inability to make controls appear semitransparent, we designed and implemented a screen overlay using the plug-in's application programming interface. This approach opened new possibilities to build more customizable user interfaces. A demonstration of the approach and sample usage of JavaScript to create buttons, draggable images, slides, and slider controls is presented.

We have developed object-oriented programming methods to enable avatar movement across the Google Earth surface in response to student actions. Students travel on their own, or in groups attached to a field vehicle avatar (a Jeep). Students communicate using text messages sent from their web pages to balloons that pop up from the avatars in Google Earth. Students can be located locally in a lab class or at great distances from one another, as in a distance education course. Our programming methods help to create a more engaging virtual field trip in which the students take the lead and decide where to go rather than simply reading text and viewing graphics in a tour designed by their instructor. The user interactivity via avatars is controlled by JavaScript and PHP. Since the position of each avatar is known, it is possible to track their movements and offer text-message advice when students stray off-task or wander about aimlessly. Our methods will be included in new virtual field trips being developed for Iceland, Hawaii, and other locations.

Google Earth includes digital elevation models and surface imagery for the Earth, Moon, and Mars, but not for Venus. To help geoscientists visualize Venusian geology, geophysics, and geodynamics, we have built a “Google Venus” virtual globe on a Google Earth foundation. We present here details of how this was done and offer regional samples to show the power of the virtual globe, combined with space mission imagery, and COLLADA models in displaying surface data and global, crust-to-core cross sections. We show how web data sources can be linked to Venusian locations in an engaging, interactive format. Our approach could be adapted to other planets and moons of the Solar System and to models of exoplanets.