German main triangular network
The German Main Triangle Network ( DHDN ) was the superordinate triangulation network of the Federal Republic of Germany . It is based on the Bessel ellipsoid , which is located in the fundamental point TP-Rauenberg (Rauenberg datum). The DHDN is the realization of the Rauenberg date. After the TP-Rauenberg was destroyed by gravel mining, the Helmert Tower near Potsdam was declared the new central point. For this reason, the Potsdam date or the Potsdam date is often used synonymously with the Rauenberg date .
With the spread of satellite geodesy , the hierarchical triangulation point network lost its importance and the ETRS89 was introduced as a spatial reference for German national surveying . a. by the satellite positioning service SAPOS and by geodetic basic network points, which have replaced the DHDN since the 2010s.
The usage coordinates of the national survey in the old federal states were based on the DHDN . Therefore, most of the spatial information was available on this date , including in particular official surveying points , topographical maps and cadastral framework maps , automated real estate maps , as-built plans from line operators, etc.
In the GDR , a largely identical system with deliberately limited accuracy was used for civil purposes (edition for the national economy, S40); For military purposes, the 1942 coordinate system (S42) was introduced in the GDR and in the Eastern European countries ( Krassowski ellipsoid with the central point Pulkowo ).
Surveying method
The DHDN has been determined by triangulation since the 19th century . Whole provinces were spanned in long chains (e.g. Hannoversche Dreieckskette) and the spaces in between were closed by filling nets (e.g. Weser network). The main triangular network was consolidated by successive networks in a step-by-step arrangement “from large to small”.
For angle measurement large served theodolites with an accuracy better than 1 "The targets were in favorable weather on the day through. Heliotrope , the sunlight in the direction of the target jet visualized reflected, or at night by artificial Lighting devices. Length of the sides of the triangle was determined indirectly: km at intervals of 200 to 300 were laid baseline (bases) of 6 to 10 km in length, which with great accuracy (to 1905 with metal rods, then with Invardrähten were measured).
The Prussian nets are stored in the Rauenberg point (Berlin) and refer to the Bessel ellipsoid as a reference surface . The azimuth from TP Rauenberg to St. Mary's Church was used for precise orientation . The scale is derived from five basic measurements ( Berlin , Braak , Göttingen , Meppen , Bonn ).
History of origin
In the Kingdom of Hanover , King George IV , who resided in London, had already ordered a survey in 1818, which was headed by the mathematician Carl Friedrich Gauß .
In Prussia , the first triangular nets were measured from East Prussia starting in 1832 along the coast to Berlin and Lübeck .
From 1866 the networks were continued westward by Oskar Schreiber ( Schreiber 's block: north of the Main , west of the Flensburg - Hof line ), so that a triangulation network was created that covered the entire Prussian state territory . As part of this project, the main triangular network in the area of today's Lower Saxony was measured by the Prussian Land Survey in the years 1875 to 1887. From the 1920s to 1945, the individual main triangular networks of the German states were merged to form the Reich Triangular Network of the First Order . In 1967 the designation German Main Triangle Network was introduced in the Federal Republic of Germany .
In the years 1955 to 1973 supplementary measurements were carried out in the Lower Saxony part of the DHDN; Until the beginning of the 1990s, the densification networks (most recently with GPS ) were re-measured.
Individual evidence
- ↑ http://www.vermessungsseiten.de/vermessungstechniker/bezsyst.htm
- ^ Peter Kohlstock: Topography: Methods and Models of Land Survey. De Gruyter, Berlin / New York 2010, p. 3ff.