TABLE OF CONTENTS Traditionally, DTMs have been derived from ground surveys, photogrammetric techniques using film-based cameras and photogrammetric plotters (in its analog or analytical form), and from topographic data using contour data, spot heights, hydrology, and boundaries (shore line, state, tile). With the increasing demand for high-accuracy elevation and terrain information, new technologies have been developed to satisfy this demand. The last two decades have witnessed a number of technological developments that have changed the way we derive and update terrain models. These advances include the systems that collect the terrain data as well as the hardware and software utilized to manipulate, manage, and analyze it. Traditional methods of generating terrain models, including manual photogrammetry and field surveying, are rapidly leaving the marketplace to the new systems that combine data from remote sensing sensors (such as digital cameras, laser, and microwave remote sensing) with direct georeferencing navigation sensors. Combining the advances in remote sensing sensors and direct georeferencing has not only increased the efficiency of DTM generation considerably, but has also resulted in greater flexibility and lower cost. This chapter will review the four most popular approaches for generating terrain data: cartographic data, optical, laser, and microwave remote sensing.
