The European Datum: A History (Part 3)

[SimonKettle]

The Central European Net (CEN )

The European datum began its life as the Central European First-Order Triangulation Adjustment (Hough, 1947) this project began in April 1945 after the U.S Third Army with the HOUGHTEAM captured the trigonometrical section of the Reichsamt für Landesaufnahme in the town of Friedrichsroda, Thuringia (after the raid in Saalfeld - part 2). This group were taken to Bamberg, in the United States Occupation Zone, for interrogation.

It was discovered that the captured Germans, led by Professor Erwin Gigas, had been completing an adjustment of the first-order triangulation of the Greater Reich with the intent to expand this adjustment across the German occupied territories...

“…the material of observation for the triangulation of Central Europe available at the end of the war was almost entirely based on new observations. Thus it appeared advisable to readjust this new material, introducing all astronomical data and the base lines remeasured in the meantime. This task was assigned to the Central Survey Office -- now known as the Land Survey Office -- an organization founded in Bamberg by the U S. Army.” Hough 1948

The assigned Land Survey Office (operating under the Army Map Service and U.S Coast and Geodetic Survey) based in Bamberg commenced the adjustment of the first-order triangulation in June 1945 (Whitton, 1952). It was here, overlooked by the US Army and led by Erwin Gigas, that the German trigonometrical section started a review of all points previously calculated highlighting those of sufficient reliability to be used in the first-order triangulation…

…by adopting the area of the whole of North Western Germany unchanged [,] use of the numerous astronomic observations was rendered impossible. Therefore, the so arising final German Reiehsdreieeksnetz, though constituting a sufficient basis for Germany herself, was no adequate nucleus for any Central European or even European Network…” Hough 1948

This review of German triangulation points created a list of data points that were originally used as area controls rather than individual arcs.  Selecting from the list of first-order points arcs were chosen and thus the framework for the triangulation adjustment was constructed. The captured Germans at Bamberg performed a least-squares adjustment of Western Europe utilising the HOUGHTEAM’s captured data (see list at the end of this blog). The work plan for the adjustment is laid out as 10 points in Hough, 1947.

The adjustment was conducted using methods like the Bowie Junction method (Adams and Oscar, 1930)  which was previously incorporated into the successful adjustment of the North American Datum 1927 (EPSG: 6267). Work was designed to follow a network of arcs following as much as possible meridians and parallels from the existing triangulation.

Bowie method is an arc method of adjusting a triangulation network, where length and azimuth of one side of a triangle at every junction between arcs (chains) are assumed correct and carried into a suitable figure of the junction. Directions or angles in arcs between these figures are then calculated, the corrections in the individual chains calculated, and the misclosures passed into the longitudes and latitudes of the initially fixed sides in the junctions by an adjustment of the entire network, using the method of least squares.

Locational calculations were incorporated from over 140 years of German records choosing the most logical values for astronomic and angle observations, bases and Laplace azimuths. This incorporation ultimately resulted in the Deutsches Hauptdreiecksnetz (EPSG: 6314).

The HOUGHTEAM was disbanded in September 1945 after completing a hugely successful operation for the war effort. During its 11-month mission the collection can be summarised as:

• Obtained complete geodetic data coverage of four provinces of Germany, discovered in the combat area, delivered direct to the artillery and put into an immediate operational use at the front.
• Selected captured enemy material shipped to Army Map Service:
  • 202 boxes of geodetic data on 900,000 stations in Europe, giving nearly complete coverage of first, second, third, and fourth control in all German and Allied operational World War II areas of the continent
  • 627 boxes of captured maps, covering approximately the same areas noted above (a)
  • Large quantities of photograph prints and dispositives for portions of above areas
  • 371 boxes of various surveying and photogrammetric instruments, including seven Zeiss stereoplanigraphs
  • Geodetic and cartographic library reference books on all countries in Europe.
• Acquisition of a nucleus of German geodesists and mathematicians and their removal to the United States Area of Occupation for use on scientific projects by U.S. forces.
• Technical supervision of the adjustment of European first-order triangulation to a common geodetic datum, ED50.
• The compilation of the magnetic atlas of Europe, epoch 1944-45, published in 1950 by the Army Map Service.

List taken from http://disturbedgeographer.com/?p=199

Whilst German triangulation and locational work was carrying on, the First International Geodetic Conference on the Adjustment of European Triangulation was held on August 7th 1946 in Paris (Hough, 1948). Here it was discussed and the decision made to examine the triangulation adjustment problem of Europe, as a whole, based on joining work currently being carried out on the Central European Adjustment with the ultimate aim of creating a common European Datum.

Due to the suffering under occupation of most European nations by the Germans contempt lay at the decision to have them involved in the project. As an alternative the United States chose the engineering task to be carried out by the Army Map Service for the first phase of the European-wide adjustment. Each nation taking part reported their…

“observed directions prepared from its latest first-order triangulation observations, its bases, Laplace azimuth, astronomic latitude and longitude observations, descriptions of stations, together with a technical report on the data with recommendations as to its use in the adjustment and relative weights to be accorded” (Hough, 1948)

…in total some 1500 first-order stations were contained in the triangulation adjustment.

The Central European First-Order Triangulation Adjustment was completed in June 1947.

The triangulation arcs can be visualized in Hough, F. W. (1947), The readjustment of European triangulation, Eos Trans. AGU, 28(1), 62–66, doi:10.1029/TR028i001p00062.

Expanding the net to create a European Datum

Other blocks were intended for connection to the Central European Net, these included a North-European Net, South-West European Net (Whitten, 1952), South East European Net and East European Net (Weber, 2000). The incorporation of these new blocks into the CEN required large amounts of calculations and processing, a primary place to introduce the use of computers. Charles Whitten, the Chief Geodesist at NOAA, and advocate of using computers to process geodetic computations passed on his methods to incorporate the blocks into a single triangulation network created the European Datum.

International cooperation

The readjustment of the Western European Bloc was completed on June 30^th, 1950 along with the combination of additional “blocks” of retriangulation which resulted in the European Datum 1950 (Hough, 1951). This is one of the first examples of true international cooperation, a project that was born out of the combination of national jealousies and war but resulted in a continent-wide standard in cartography, positional science and the study of the shape of the Earth.

Fittingly Floyd Hough wrote appropriate words on the creation of the European datum placing it as one of the major projects of cooperation in European and world history born out of the contrasting chaos of war.

“The term ‘cooperation’ is one of the most satisfying and comprehensive words in the English language. If we were to have complete cooperation in all matters between individuals and nations, the acme of human aspiration would be reached; selfishness would be abandoned; universal peace would be a fact; the millennium would be at hand.” Hough, (1951)

The triangulation was tied to the International Ellipsoid 1924 (Hough, 1948) built upon some 173 astronomic latitudes, 126 astronomic longitudes and 152 azimuths (Barsky, 1971), no one station can be designated as the datum origin rather a fundamental point is designated at the Helmert Tower in Potsdam, Germany (52°22’51.45”n Latitude 13°03’58.74”e longitude). The design of the first-order triangulation network was designed so that any further triangulation and positional calculations were made using this rigid base, as Hough (1948) described:

“Interior triangulation of the area can be adjusted at will to this rigid framework much as the inner portion of a modern steel building is fitted to its network of beams and columns.…” Hough 1948

This was the story about how the European Datum of 1950 was created and has formed the basis of a standard positional framework for the European Continent.

The European Datum 1950

Origin: Potsdam (Helmert Tower). 52°22’51.45”n Latitude 13°03’58.74”e longitude

Ellipsoid: International 1924

Prime Meridian: Greenwich