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# What Does a Photogrammetrist Do?

C.B. Fox
C.B. Fox

A photogrammetrist uses two-dimensional photographs in order to reconstruct an environment or object in three-dimensions or to determine the actual sizes and distances of real-world objects from photographs. These professionals use geometry and optics in their work and are often aided by computer programs that help them solve complicated mathematical problems. It is possible to find photogrammetrists working in a variety of different fields. Some of the more common jobs for photogrammetrists are found in police investigation, insurance, mapmaking, and engineering.

In its simplest form, photogrammetry uses only one photograph to collect information about the real world. If the scale of the photograph to the actual object is known, the picture can be measured and the actual size of the object easily calculated. Though it can be this easy, the vast majority of photogrammetry is performed using a series of photographs and complicated equations.

In photogrammetry, when a series of pictures are taken of the same subject, the position and orientation of the camera is changed from one picture to another. In order to get information about the photographed object, a photogrammetrist must identify a point that appears in two or more pictures and compare the way that the point moves in relation to the rest of the objects in the photograph. In many cases, information is gathered from multiple points on a series of photographs at once. Though the calculations needed to gather information about many points are complex, the use of computers makes it possible for a photogrammetrist to generate this information quickly and reliably.

One of the more common things a photogrammetrist does is to create topographical maps. In order to make these, the photogrammetrist uses a series of aerial photographs taken by a low-flying plane. Points are identified in the pictures and then compared as the camera moves across the landscape in order to reconstruct depth from the two-dimensional image. Once the depths of various points have been determined, a map of the elevation of various sections of terrain can be created. These same techniques can be used to determine the topography of a cityscape, an archeological dig, or a geometrical formation.

Photographs of smaller subjects may also be analyzed by a photogrammetrist. Insurance and police investigations often employ these professionals in order to determine how much an object has been damaged. By reconstructing these objects, often through the use of three-dimensional computer modeling, a photogrammetrist can determine how far an object, or a piece of it, was displaced. This information can be used to determine the force that was needed to damage the object, which is particularly useful in determining such things as the speed a car was moving at the time of an accident.