First order network
As a first-order network, or “ first-order ” for short , a geodesist refers to the basic network of a national survey .
The fixed points are about 25–50 km apart and have a terrestrial line of sight in good weather conditions . Traditionally one also speaks of
- Triangulation or triangular network , although more distances ( trilateration ) are measured today than angles . Besides exist
- Satellite networks ( measured by GPS or other methods). They can even be of the zero order if the distances are around 100 km and are suitable as a higher-level control network.
Is marketed with z. Sometimes chest-high measuring pillars or with rock marks and additional secondary points (e.g. wall bolts , church spire cross ). Terrestrial measurements are made with theodolite or universal instrument and electronic distance meter .
The accuracy is better than ± 0.5 "( arcseconds on the globe) (in Central Europe 0.2-0.3"), which means about 1: 1 million (3 cm at 30 km) due to the network association. The network benefits from the fact that, due to the long triangle sides, there are hardly any steep visures and therefore the standing axis error and the vertical deviation have little influence.
In addition to basic surveying, modern first-order networks are also suitable for geodynamic purposes (determination and monitoring of earth crust movements ), especially if they are supported by newer electronic distance measurements . Such movement measurements can be found e.g. B. periodically in the Southern Alps (Austria / Slovenia) and the Western Carpathians (Slovakia / Poland).