ElevationFile is an abstract base class used to define the interface
between files holding terrain data and the JAVA3D classes that
convert the terrain data into geometric primitives.
Constructor is reponsible for setting up the appearance/material,
computing the triangle strip values (colors, normals, coordinates)
stored in vertexData, then creating the actual JAVA 3D geometry.
This class is used to store the ground coordinates of a terrain data segment
the latitude and longitude of each corner of the terrain area are stored in
arc-second units
process keyboard input
up arrow - move forward
down arrow - move backward
left arrow - turn left
right arrow - turn right
U, u - increase altitude
D, d - decrease altitude
Loads elevation data file specified in first entry the cmdLine argument
if there is no command line then display a filedialog to allow the user to
choose the file.