This paper presents a method for obtaining accurate dense elevation and appearance models of terrain using a single camera on-board an aerial platform. Applications of this method include geographical information systems, robot path planning, immersion and visualization, and surveying for scientific purposes such as watershed analysis. When given geo-registered images, the method can compute terrain maps on-line in real time. This algorithm, called the Recursive Multi-frame Planar Parallax algorithm, is a recursive extension of Irani et al.'s multi-frame planar parallax framework and in theory, with perfectly registered imagery, it will produce range data with error expected to increase between linearly and with the square root of the range, depending on image properties and whether other constants such as framerate and vehicle velocity are held constant. This is an improvement over stereo systems whose expected errors are proportional to the square of the range. We show experimental evidence on synthetic imagery and on a real video sequence taken in an experiment for autonomous helicopter landing.