Observer3D moves the view over terrain in Java 3D 1.5.2 based on mouse movements. It is designed for use with open ground (as opposed to deep space, air, underwater, caverns, and other indoor spaces). It was written originally for a fast-paced game, and so had to be highly responsive and intuitive to enable the user to focus on and control the action A sample program is included with the source code that demonstrates mouse clicks, labels on objects the mouse is hovering over, and pop-up menus. It has a 2D map with the area visible in the 3D view outlined in orange. It also demonstrates the ease of maneuvering over the terrain.