Baseline Unterföhring – Aufkirchen

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Map from 1801 with the base line Unterföhring – Aufkirchen

The base line Unterföhring – Aufkirchen is the starting line measured in 1801 under the direction of the French Colonel Charles Rigobert Marie Bonne for the subsequent Bavarian triangulation , which lasted until 1828

history

Elector Maximilian IV. Joseph (later King Maximilian I), who was advised by his minister von Montgelas , founded the Topographical Bureau on June 19, 1801 (forerunner of the Bavarian Land Surveying Office). He demanded a “complete, astronomically and topographically correct” map of Bavaria ( Philipp Apian had previously mapped Bavaria in the 16th century).

In order to be able to produce them, a large-scale trigonometric surveying network has to be formed, in which the position of the surveying points , then usually church towers, is precisely determined by triangulation , i.e. by measuring the angles of the triangles. However, the side length of these triangles can only be calculated if a side length, ie the length of a base line several kilometers long, is precisely measured beforehand .

Colonel Charles Rigobert Marie Bonne (1771–1839) (not to be confused with the cartographer Rigobert Bonne , 1727–1795) was an engineering geographer of the French Armée du Rhin under General Moreau , who remained in the country after the occupation of Munich and the Peace of Lunéville was.

In search of a suitable area for a baseline, he and the Bavarian Colonel von Riedl visited the Erdinger Moos (northeast of Munich), a moorland that was almost deserted at the time. In the vicinity of Aufkirchen , a district of the municipality of Oberding , there was a hill from which several distant places (Munich, Dachau, Freising and others) could be seen. At that time there were no high vegetation or even larger buildings in the area. Near Munich, near the village of Oberföhring, there was a hill from which one could see the towers of the Frauenkirche and in the opposite direction the hill at Aufkirchen and its church. Colonel Bonne checked from the north tower of the Frauenkirche with a telescope that a straight, undisturbed line could be set up there. The inspection of the terrain by an officer showed that a large part of the area was knee-deep under water, but underneath there was solid gravel, and that the water could be partially drained off by cleaning the streams. It was seen as an advantage that the work in this area could not be disrupted by carts or bystanders.

The two end points of the route were then marked with high signal poles. Then the numerous ditches and streams were bridged with footbridges and the route made accessible. For the measurement, absolutely horizontal bars were set up on adjustable supports, which served as a base for the basic apparatus from the actual measuring rods. When setting up the jetties and choosing the base equipment , Colonel Bonne benefited from the experience the British had made a good ten years earlier at the base line at Hounslow Heath .

The basic apparatus essentially consisted of five stiffened fir wood slats , each 5 m long. To protect them from moisture, they had been painted several times with oil paint to keep changes in length as small as possible. Their ends were provided with precisely machined brass sleeves so that they could be placed exactly against one another.

The measurements began on August 25th and lasted until November 2nd, 1801. Each of the 5 measuring rods was carefully laid out so that the others were not shifted. Their position was then checked and the length measured and the temperature, humidity and weather conditions noted. Then the first yardstick was placed in front of the fifth and the process started again. Immediately after the external work was completed, Bonne wrote a report on the basic measurements ("Construction de la Carte de Bavière", with an addition from 1803: "Fixation de finitive de la longueur de la Base de la Goldach", today in the Bavarian State Archives ), in which he made corrections because of the temperature and humidity-related changes in length of the staff. The change in length of his brass meter model was converted to that of the original meter . In order to make the baseline comparable with those of other countries, it was converted to sea level.

  • Base pyramid Unterföhring

  • Base pyramid Aufkirchen

The length of the base was determined to be 21,653.80 m . In order to be able to measure the base line at any time, but also as a memorial for this milestone in the history of Bavarian land surveying , stone pyramids ("base pyramid") were erected over the two endpoints in 1802 (the pyramid in Unterföhring is north of the Föhringer Ring and Kreisstraße ▼ junction , the one in Aufkirchen am Kraftwerk ▼ ). One of Bonne's original measuring rods can be viewed in the surveying history exhibition at the State Office for Digitization, Broadband and Surveying in Bavaria . The measurement technology used today, supported by satellites, confirms the accuracy of the results from 1801: Bonne was only less than 1 m wrong. The meter was only introduced in revolutionary France in 1795. Therefore, the base length was converted into a measure familiar to Bavaria at the time: 7,419.267 Bavarian rods (1 rod = 10 shoes = 2.91859 ... m).

The spire of the north tower ▼ of the Munich Frauenkirche (the zero point of the Bavarian land survey), the two pyramids (the ends of the base line) and the spire of the parish church of St. Johann Baptist in Aufkirchen ▼ lie on the same straight line. The distance between Frauenkirche and Unterföhringer Pyramid is about 6,450 m and that between Aufkirchener Pyramid and parish church is about 400 m.

literature

  • Günter Nagel: The basis of Charles Rigobert Marie Bonne . Bulletin of the German Association for Surveying, 2001, No. 53, 2.
  • Achim Fuchs: How it all began - The establishment of the Topographical Office in Munich in 1801. In: 200 Years of Bavarian Surveying Administration 1801–2001 , Bavarian State Ministry of Finance (Ed.), P. 26 (p. 24 in PDF)
  • K. Tax Cataster Commission in association with the topographical bureau of the K. General Staff (ed.): The Bavarian land survey in its scientific basis . Academic book printing by F. Straub, Munich 1873 ( full text in the Google book search).

See also

Web links

Commons : Baseline Unterföhring – Aufkirchen  - collection of images, videos and audio files

Footnotes

  1. ↑ In some sources, the Oberföhring belonging to Munich is mistakenly named as the southwestern end of the baseline. As early as 1801, the Ministry of Finance wrote of a baseline on the level between Ober-Vöhring and Aufkirchen (Fuchs: How everything began , p. 34, 32 in the PDF). Today the end point is only approx. 100 m from the Munich city limits.
  2. ↑ The Bavarian State Survey in its scientific basis, pp. 3–34
  3. ↑ Bavarian land survey. In: Chronicle of the community Unterföhring
  4. ^ Aufkirchen ( Memento from July 30, 2012 in the Internet Archive )