Arc measurement

[1] Arc measurement campaigns in Europe were the precursors to the International Association of Geodesy (IAG).

[5] Nowadays, the method is replaced by worldwide geodetic networks and by satellite geodesy.

The first known arc measurement was performed by Eratosthenes (240 BC) between Alexandria and Syene in what is now Egypt, determining the radius of the Earth with remarkable correctness.

This is a partial chronological list of arc measurements:[7][8] Assume the astronomic latitudes of two endpoints,

(forepoint) are known; these can be determined by astrogeodesy, observing the zenith distances of sufficient numbers of stars (meridian altitude method).

Historically, the distance between two places has been determined at low precision by pacing or odometry.

High precision land surveys can be used to determine the distance between two places at nearly the same longitude by measuring a baseline and a triangulation network linking fixed points.

Additional arc measurements, at different latitudinal bands (each delimited by a new pair of standpoint and forepoint), serve to determine Earth's flattening.