BASE LINE

1. (surveying) A surveyed line established with more than usual care, to which surveys are referred for coordination and correlation. 2. (photogrammetry) The line between the principal points of two consecutive vertical air photographs. It is usually measured on one photograph after the principal point of the other has been transferred. 3. (radio navigation systems) The shorter arc of the great circle joining two radio transmitting stations of a navigation system. 4. (triangulation) The side of one of a series of coordinated triangles the length of which is measured with prescribed accuracy and precision and from which lengths of the other triangle sides are obtained by computation.