Photogrammetric Instruments

instruments designed to measure the size, shape, and position of objects from aerial, space, or ground photographs. Such instruments are widely used in the compilation of topographical maps and in geological, forest management, road, and other engineering surveys. They may be designed for work with single photographs (monocular instruments) or with pairs of photographs (stereophotogrammetric instruments).

Monocular instruments include measurement magnifiers for aerial photo interpretation, comparators for measuring the coordinates of points on a photograph, rectifiers for obtaining a horizontal image of a site in order to compose a controlled photomosaic, single projectors for transferring an object from a photograph to a plotting table, and enlargers and reducers for altering images to a given scale.

Stereophotogrammetric instruments include instruments for the measurement and marking of photographs and instruments for determining the coordinates of points and constructing and measuring models from photographs (general-purpose stereophotogrammetric instruments).

Measuring photogrammetric instruments include stereometers for determining the height of objects and for laying horizontals and stereocomparators for measuring the coordinates of points on photographs; the latter are widely used in aerial triangulation. General-purpose photogrammetric instruments include twin projectors, multiplexes, topoflexes, and other optical instruments; stereographs, stereoprojectors, stereoautographs, topocards, autographs, and other mechanical instruments; and photographic-stereographs and other opticomechanical instruments.

Highly accurate analytical instruments consisting of a stereo-comparator, digital computer, and coordinatograph form a special group of general-purpose photogrammetric instruments; they make it possible to measure photographs with an accuracy of 2–3 micrometers. Such instruments are used for preparing outlines, maps, and photomosaics as well as digital models of sites.