Northstar

SURVEYING, INC. 

INTEGRITY & EXCELLENCE SINCE 1979

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The practice of obtaining surveys by means of photography. The camera commonly is airborne with its axis vertical, but oblique and horizontal (ground-based) photographs also are applicable. Data reduction is accomplished by stereoscopic line-of-sight geometry with use of both analytical and analog methods. In vertical aerial surveys adjacent photos are overlapped. The two images of the same terrain are then superimposed for three-dimensional viewing by human operators or automated sensors.

In a widely used analog procedure the two photos are placed in the projectors of a stereoplotting instrument. With the aid of visible ground-control points the photos are oriented to the relative positions they had at the instants of exposure. In a typical automated stereoplotting system  scanning devices substitute for human eyes to sense model-surface slope and thus to control servomechanisms that raise and lower the plotting table and translate it along a succession of closely spaced parallel horizontal dimensions, or ground profiles.

            

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Last modified: 01/29/09 Thomas McGee