Photogrammetry

Abstract

Photogrammetry is defined by the American Society of Photogrammetry as the art, science, and technology of obtaining reliable information about physical objects and the environment through processes of recording, measuring, and interpreting photographic images and patterns of recorded radiant electromagnetic energy and other phenomena. As implied by its name, the science originally consisted of analyzing photographs. Although photogrammetry has now expanded to include analysis of other records, such as radiated acoustical energy patterns and magnetic phenomena, photographs are still the principal source of information. In this text "photographic" photogrammetry is emphasized. Included within the definition. of photogrammetry are two distinct areas: (1) metric photogrammetry and (2) interpretative photogrammetry. Metric Photogrammetry consists of making precise measurements from photos and other information sources to determine, in general, the relative locations of points. This enables finding distances, angles, areas, volumes, elevations, and the sizes and shapes of objects. The most common application of metric photogrammetry is the preparation of planimetric and topographic maps from photographs. The photographs are most often aerial (taken from an airborne vehicles), but terrestrial photos (taken from earth based cameras) are also used. Interpretative photogrammetry deals principally in recognizing and identifying objects and judging their significance through careful and systematic analysis. It includes branches of photographic interpretation and remote sensing. Photographic interpretation involves the study of photographic images, while remote sensing, which is a newer branch of interpretative photogrammetry, includes not only the analysis of photography but also the use of data gathered from a wide variety of sensing instruments, including multispectral cameras, infrared sensors, thermal scanners, and side-looking airborne radar. Remote sensing instruments, which are often carried in vehicles as remote as orbiting satellites, are capable of providing quantitative as well as qualitative information about objects. At the present time, with our recognition of the importance of preserving our environment and natural resources, photographic interpretation and remote sensing are both being employed extensively as tools in management and planning.