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Java 3D is a full-featured 3D graphics API that has been evolving over the past five years. Resources provides a link to Sun Microsystems' Website, where download and installation notes can be found. Java 3D supports a range of applications, including computer-aided design, Web advertising, motion picture special effects, and, of course, computer games. Java 3D uses conventions resembling OpenGL, but is actually a layer that sits atop low-level graphics APIs such as OpenGL and DirectX. Java 3D, like Java, is platform independent.
Geographic information system (GIS) developers wishing to expand into the 3D world and game developers looking for an alternative to virtual world representation appreciate the difficulty in creating virtual worlds that accurately portray the real world and can be navigated by interactive programs. Java 3D provides powerful and efficient mechanisms to display virtual worlds and convenient user interfaces to manipulate the worlds' views. In this article, I describe how to load and display data available from the US Geological Survey (USGS) in DEM (digital elevation model) format and how to create a user interface that allows keyboard and mouse controls to navigate through the virtual world. Figure 1 presents an aerial view of the Grand Canyon created by the application. The application's complete source code and Javadoc HTML files are available in Resources, as is a link to the USGS Website where the data resides.
Figure 1. Aerial view generated by demonstration application
To display a virtual world, a data file containing the coordinates of the hills, valleys, rivers, and oceans is necessary. You can either create this yourself or use an existing one. The USGS has such files available for download in DEM format. A digital elevation model consists of a sampled array of ground elevations (in meters) for positions at regularly spaced intervals. The basic elevation model is produced for the Defense Mapping Agency (DMA) and is distributed by the USGS and EROS (Earth Resources Observation System) Data Center in the DEM data record format. The 1-Degree DEM (3-by-3 arc-second data spacing) provides coverage in 1-by-1 degree blocks (about 68 miles by 68 miles) for the entire continental United States, Hawaii, and parts of Alaska. The 3-by-3 arc-second spacing results in a 1,201-by-1,201 array of elevations for each 1-degree block, or roughly one elevation measurement every 92 meters or 100 yards.
A newer STDS (Spatial Data Transfer Standard) format is also available. These elevation readings can be used to create 3D representations of the landscape, referred to as terrain modeling. When combined with other data types, such as stream locations and weather data, these readings can also be used to assist in forest fire control, determine the volume of proposed reservoirs, calculate the amount of cut-and-fill materials, and assist in determining landslide probability. Along with these useful applications, DEM data can make for realistic virtual worlds for gaming.
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