Typically an image taken from a satellite is draped over elevation data and FLY! is used to fly through the data from a person's perspective on the ground.
The user has full control over the flying elevation, direction and speed. Rendered scenes can be saved to disk in a variety of file formats for later use. A simple flight plan can be made to fly through the terrain.
Sources of data include: satellite (Landsat, Spot, ...), air photo, scanners, and GIS systems.