Baltic ring

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The Baltic ring (engl. Baltic ring , dt. Also Ostseering ) is a cross-national survey network , all the coastal areas and neighboring states of the Baltic Sea connects and the form of an annular, 2500 kilometers long, usually double Triangulationskette has. This major project, exemplary for geodesy in the interwar period - it represented the first truly international triangulation network and was created before the similarly conceived projects of the Soviet network and the European network , the first section of which it formed - was the first large network of a mathematically strict astrogeodetic network adjustment that included numerous Laplace points , which increased its accuracy to 0.3 "(1.5 ppm or 15 cm per 100 km) , which at that time seemed unattainable  .

The ring network comprises around 150 points of the first order , the distances of which are on average around 40 km (depending on the topography 25 to 60 km) and stretched from northern Germany and western Prussia as a double chain over small parts of Poland to East Prussia and over the rest of the Baltic States ( Lithuania , Latvia and Estonia ) to southern Finland , followed the Gulf of Finland to central and southern Sweden and across the Danish Sound back to the mainland to the Berlin hub .

The adjustment (minimization of the residual errors) was carried out on the basis of Helmert 's point projection using the correlate method (a kind of conditional network adjustment). First, the commission weighed this method against a compensation according to coordinates ( mediating compensation ) and then decided on it after Ölander had achieved the best results for the southern Finnish triangular wreath. The ring around the Baltic Sea was broken down into nine triangulation chains, which followed a large ninagon and each was balanced individually taking into account the baseline and Laplace conditional equations (today the same idea is followed in international networks in militarily critical areas because it supports the data exchange the point coordinates only possible at the nodes, while the coordinates of the remaining survey points are reserved for the sole right of disposal of the individual states).

In detail, the network geometry differs considerably between the individual states, so that some “weak points” could impair the accuracy of the overall network. Although the geometry of single chains (stringing together of individual triangles ; especially in the Baltic States and south-western Finland), double chains (two directly connected single chains; especially in Germany, Denmark and Finland) and quadruple chains (in East Prussia) to high-precision trusses and three frame nets ( in Sweden) changes, the network quality is relatively uniform.

The nine- cornered polygon was grouped around nine regional nodes (Germany 2, Baltic States 2½, Finland 1½, Sweden 2, Denmark 1). In terms of national surveying , the three crossings of straits were particularly critical and required great care in terms of measurement technology and a theoretically well-founded compensation of the directional measurements . The astronomical- geographical length difference measurements between the network nodes and the regional centers were just as thorough .

The adjustment itself was carried out using a correlate method and the solution of the system of normal equations, which was huge for the computing aids at the time, was carried out using the elimination method of Gauss and von Choleski- Rubin. For the conditional equations of the Laplace points, Ölander's method (directly in the adjustment of the triangular chains) proved to be superior to that of Krassowski (iterative, strict conditions only in the main adjustment ). Other variants were developed by the German geodesist Eggert (co-author of the Handbuch der Vermessungskunde ) and the Swede Asplund , but were only used on a larger scale in the later European network .

A preliminary conclusion of the calculations took place after the 9th meeting of the Baltic Geodetic Commission (Helsinki, 1937) and then by the army survey of the " Third Reich ", the final one under the aegis of the USA between 1946 and 1950 within the German Central European Network (ZEN , Head: Helmut Wolf ) and the European network .

However, the cooperation of the surveying authorities suffered a severe setback after 1945 due to the Cold War , from which they could no longer recover. A broad Northern and Western European cooperation for the establishment of the ReTrig and the ED50, and later for the expansion of the WEST (Western European satellite network) to Central and Eastern Europe soon became more important .

literature

  • Karl Ledersteger : Astronomical and Physical Geodesy. In: Jordan, Eggert, Kneissl: Handbuch der Vermessungskunde Volume V (871 p.), Chapter IV (§ 27 and 25), JB Metzler, Stuttgart 1969
  • Th. N. Krassowskij: Calculation method for triangulations of the 1st order in the USSR . 5th meeting of the Baltic Geodetic Commission, Copenhagen / Helsinki 1930/31 (translation by Max Kneissl in Cartography and Surveying, Berlin 1942)
  • B. Jeschke, B. Kodatis: Determination of the difference in length between Potsdam and Danzig. The length determination of the regional headquarters Kaunas (Lithuania) –Potsdam. Special publication No. 5 of the Baltic Geodetic Commission, Helsinki 1936, 72 p.
  • VR Ölander: Weights of the azimuths and coordinates in a schematic triangular chain with Laplace equations. Negotiation of the 9th session of the Baltic Geodetic Commission (July 1936), Finnish Geodetic Institute, Helsinki 1937.