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Earth Animations for Education from NASA

Contents The Scientific Visualization Studio SVS Animations in Your Software    EarthFlicks, the Example Application Step 1: Determining What's Available    Describing a Capabilities Entry Step 2: Forming Requests and Retrieving Images    Threaded Retrieval Step 3: From Image to Texture Map Step 4: Displaying and Animating the Images Playing with the Globe Conclusion Resources

You've seen the beautiful images of Earth from space taken by NASA astronauts and satellites. By viewing a series of images one after another like frames of a movie, we can watch changes to the Earth as they happened. You can follow hurricanes moving towards land and observe ice caps contracting. You can replay and study changes due to weather, natural events, and human activities. NASA has assembled dozens of such animations, all free. This article describes how to write Java software that uses the OpenGL graphics interface to display these images on a 3D globe.

The Scientific Visualization Studio

A team of expert scientists, engineers, and artists at NASA's Scientific Visualization Studio (SVS) carefully compose these animations. This group performs their magic at NASA's Goddard Space Flight Center in Maryland. They have been creating animated visualizations of Earth and space science data for over 15 years. They select images from a seemingly infinite collection of NASA imagery. They design each animation to illustrate a particular phenomenon or event. Here are two examples:

Figure 1. African fires during 2002

Figure 2. Atmospheric water vapor during 1998

Recently, SVS established an image server to make some of the best earth science animations available programmatically over the internet to software applications. Currently about 80 are available; that will grow to over 130 by October, 2005. You can see the growing list at the SVS server site. The full SVS catalog contains over 2500 animations and is at the SVS home page.

SVS animations dynamically illustrate the formation of what's shown in these static images: The fires in Africa progress southwards with the season. The vapor and rain (yellow) flow across the globe as the days progress. You can see more single shots like those shown above at the SVS website, but they're really meant to be seen "in motion," wrapped around a 3D Earth. The SVS website doesn't do that. You need a software program running on a local computer to get the full effect. You also need the ability to interact with the model by turning the world around and zooming in and out. In this article, I describe a bare-bones program, in order to keep the code easily understandable. The best program for viewing SVS animations is the free and open source program NASA World Wind.

SVS Animations in Your Software

SVS imagery is designed to be used in educational software. The web service responds to HTTP requests by returning an image. There's a strict protocol and request language, with the request parameters tacked on to what we'd consider a conventional URL.

Four steps are required to retrieve and display SVS animations in 3D:

1. Query the SVS server to determine the animations that are available from the server's table of contents.
2. Form and send requests and retrieve the images of the animation. Each image requires a separate request.
3. Convert the images to texture maps so they can be wrapped around a globe using OpenGL.
4. Display the images in sequence to "play" the animation.

EarthFlicks, the Example Application

The code I'll use to demonstrate and explain all this is a small Java application called EarthFlicks, which is available for download at the end of this article. EarthFlicks creates two windows: one for selecting and retrieving animations from SVS, the other for showing and playing them. Figure 3 shows what it looks like:

Figure 3. EarthFlicks

Selecting an animation in the table and clicking the Import button causes EarthFlicks to retrieve and cache locally all the images for that animation. When they are subsequently played, EarthFlicks recognizes them in the cache and draws the images from there, rather than from the SVS server.

EarthFlicks has been kept as simple as possible in order to keep its code clear and useful in a tutorial. However, retrieving and playing SVS animations requires a lot of code; more than I would have guessed before I started writing EarthFlicks. Not all of that code can be listed in this article. What are listed are important details unique to the task. The rest is documented in the source files themselves, which are available at the location mentioned above.

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