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BACKGROUND INFORMATION

Photogrammetry is the term used for the science and technology of obtaining reliable measurements of an object from photographs taken at a distance. These measurements are used to produce maps, digital elevation models, and other Geographic Information Systems (GIS) data. Photographs can be taken with either film-based or digital equipment from either an aerial or ground-based platform. An aerial platform can be a satellite or conventional aircraft, and a ground-based platform is usually a tripod.

Remote sensing is another term for studying images taken from a distance. Photography is one type of remote sensing. Other types include radar, laser, and ultrasound. Active sensors like radar or laser send out a pulse and get back either a return sound (radar or sonar) or a return light (laser or LIDAR). LIDAR stands for Light Imaging Detecting and Ranging. These forms of imagery capture the geographic coordinates of a subject, not an exact image.

Because photogrammetry records and extracts the detailed image of the subject at a given time, photography (either digital or film) is primarily used because it can capture an actual image of the subject.

Professional photogrammetrists are responsible for all phases of a mapping project. They plan and supervise ground and aerial surveys, interpret and make measurements from remotely sensed images, and design maps and presentations. Like Neffra, they can also manage the general business aspects of a project.

History

The concept of reproducing a subject, using lenses and the principles of geometry and perspective to make accurate measurements probably began with Leonardo Da Vinci around 1492. These techniques were investigated even before camera systems, as we know them today, were developed. Some very early cameras and photographs were used as measuring devices during the Civil War, when the Union Army used cameras based in tethered balloons for reconnaissance purposes.

The science of photogrammetry--making measurements from aerial photographs--gained popularity during the 1930s and 1940s, when topographic mapping was used for military applications during World War II. The combination of good quality, large-format aerial cameras, the stability and maneuverability of "modern aircraft," and the optical precision of binocular viewing instruments facilitated its widespread use in mapping.