Laplace azimuth
As Laplace azimuth is accurate to the influence of the vertical deflection reduced azimuth (between two survey points points trigonometric ) the net first order called. It is used to control and correct the error propagation in extensive triangulation networks .
Determining a Laplaceazimuth involves:
- the precise measurement of one or two astronomical azimuths, with the trigonometric points at least 20 km apart;
- the measurement of both vertical deviation components and (north and east components);
- the correction of the astronomical azimuth (with respect to the true perpendicular) to a geodetic azimuth (with respect to the reference ellipsoid of the national survey).
The fundamental points of many national surveying networks, which were mostly established in the 19th century, show small systematic errors , which mainly stem from the then still difficult time determination . Such influences act as outwardly increasing twisting of the network, which can amount to a few cm / km at the edges of larger states and is called the Laplace contradiction . They can be determined by means of some Laplace azimuths distributed in the network and almost eliminated using modern network adjustment methods. One of the first transnational projects in which direction control was carried out with Laplace azimuths was the European network and its date transition from the ED50 to the ED79 .