The AGA-6 Geodimeter
Like any light-based electronic distance measuring instrument, this device emits a beam of light that is reflected through a prism with mirrors. Determining the time difference between initially emitted beam and the reflected beam enables the distance between the device and the mirror to be determined.
This device was designed by the Swedish physicist Erik Bergstrand in 1948 and was used from 1953 onwards to measure long distances (up to 20 km) to an accuracy of several centimetres.
In order to achieve this degree of accuracy, the time interval between the emission of the beam and its reflection must be determined with great accuracy. This is only possible indirectly, through the principle of phase measurement.
This distance meter (and its successors) was used in Belgium in the 1960s and 70s to measure distances in the geodetic network for Belgium. This is a network of triangles for which the corner points have been accurately determined, which is indispensable for creating homogenous series of topographical maps. For the measurement of long distances, both the device and the prism must often be set up on clearly visible high points, such as church steeples, water towers or masts.
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