stereocomparator

a stereophotogrammetric instrument designed to measure the X and Y coordinates of points on photographs. In terms of design, stereocomparators are subdivided into instruments with separate (independent) movement of the carriages of the left and right photographs and instruments with joint (dependent) movement. In the first type, the A” and y coordinates of conjugate points on the two photographs are measured, while in the second type the coordinates of a point on one of the photographs and the longitudinal (p) and transverse (<_ir) parallaxes are measured. (Parallaxes are the differences in the coordinates of a conjugate point on adjacent photographs; the longitudinal parallax is the difference in abscissas, and the transverse one is the difference in ordinates.)

Figure 1. Diagram of a stereocomparator

Figure 1 is a diagram of a stereocomparator with dependent carriage movement. Control lever 2 displaces carriage 1, which carries both photographs, by a quantity X, while optical system 3 is displaced by a quantity Y. The right photograph is additionally displaced by quantities p and q.