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Sion - the 1831 baseline

The magnificent cultural and historic achievement of the Dufour map is due among other things to the fact that this work was created against the background of an as yet ununited nation. Dufour therefore had to rely on a major collaborative effort of experts from the individual cantons.

Painting with portrait of Josef Anton Berchtold
Josef Anton Berchtold, 1847, from "History of Valais", 3.2

 

One example of this principle of federal cooperation is the work of the Sion-based Canon Josef Anton Berchtold (1780-1859). Following the rejection of his theological writings, he dedicated himself to mathematics and natural science studies. He began the preparations for his magnum opus, the trigonometric survey of his native canton, around 1826.

Berchtold was already 51 years old when, in March 1831 in Champsec, east of Sion, he measured a baseline of 2,095.82 metres with iron poles. It is from this baseline – put simply – that the dimensions of the Valais were measured. He was able to measure horizontal and vertical angles with a theodolite. As shown in Figure 2, the length of his baseline (a-b) over the mid point at Nax (n) was transferred to the triangle side Mont d'Orge-Lens marker (m-l). In his first grid, he even surveyed the Cathedral of Sion where, two years before, he had still conducted mass. He wanted the coordinates for the canton of Valais to be referenced by it.

Original sketch
Figure 2: The baseline in Champsec near Sion in Berchtold's calculations. Swiss Federal Archives SFA, E27/21090, p. 135.

It was first necessary to integrate the “Base de Sion aux Champs secs” baseline, which previously had no identifiable location. A GIS (geographic information system) showed that it did not match the national map and was thus not to scale. A small triangular grid was set up on the basis of Berchtold's notebooks from the federal archives. The triangulation grid was equalised following translation of the data into the input format of LTOP, the triangulation adjustment software. The results of this “free grid” (Figure 3) substantiate the high quality of Berchtold's observations: the maximum directional correction was 18.8 mgon and the maximum transverse deviation 117 mm over a distance of 16.2 km. 

Extract of map of the Sion region with marked measurement points and lines
Figure 4: Subgrid for integration of the Sion baseline into the current reference system. The coordinates of both baseline endpoints, marked with a black triangle, were identified. Map background: LK100

Fig. 4 shows how the direct measurements of the baseline on the ground were transferred to the Mont d'Orge–Nax triangle side in such a way that the distances between all trig points and their coordinates could then be calculated. From 1836, Berchtold was energetically supported by his nephew Josef Anton Müller (1816–1881), who was only 20 at the time. In 1844, uncle Berchtold and nephew Müller were able to complete the triangulation of the canton of Valais. The incredibly comprehensive work is collected in the Valais state archive. The 1,500 pages of calculations contain the 153 trig points and 7,500 angles measured along with the calculations for 850 points. 
Following the conclusion of the work, the canton of Valais was ready for the topographic survey relating to the Dufour map. 

Original sketch
Figure 5: The Sion baseline and its transfer to the nearby Mont d'Orge–Nax trig points in the grid as measured by Canon Berchtold in 1831. Map background: original 1:50,000 survey 407 (reduced and reproduced here) of 1841 by the engineers and topographers Isaac Christian Wolfsberger (1801–1876) and Adolphe-Marie-François Bétemps (1813–1888), therefore about a decade after the baseline measurement. swisstopo, map collection, LT OA 407.

Documentation

  • Sion: 1831 baseline
    Josef Anton Berchtold was already 51 years old when in March 1831 he measured a baseline of 2,095.82 metres in Champsec, to the east of Sion, using iron rods. Here the idea was to measure the size of the canton of Valais using this baseline. Berchtold’s most important instrument was a theodolite, which he arranged to be made on the basis of a wooden model constructed by Jakob Kern (1790 to 1867) in Aarau.
    PDF, 4 page(s), 742 KB, German

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