The internal surveying of a tunnel is carried out using a surveying theodolite. This theodolite, which is now available as a 3D model, was used for surveying the Lötschberg tunnel.
The triangulation of Lötschberg tunnel was carried out between 25 August and 8 September 1906 – the same year that the Simplon Tunnel was opened. 1 The task was carried out by Th. Mathys, who was concordat surveyor and assistant to the cantonal surveyor in Bern. Due to time constraints, he limited himself to correlating the specified end points of the tunnel using a simple triangulation. 2
The surveying theodolite required for the internal surveying of the tunnel was ordered by Mathys from Kern & Co. in Aarau. This company’s order book shows that it was a theodolite without graduated circles, featuring 35x magnification and a three-part apochromatic lens. The theodolite under serial number 18642 has three levels – two perpendicular alhidade levels and one Zwicky rider level on the horizontal axis. The surveying theodolite was delivered in January 1907 at a price of CHF 1081.50 plus about CHF 120 for a leather case and a transport box.
However, the internal surveying of the straight tunnel axis, for which this theodolite had been ordered, ultimately was not carried out by Th. Mathys. After his unexpected death in autumn 1907, the surveying work was taken on by Fritz Bäschlin.3 Bäschlin was working as a surveyor for the Swiss Federal Topography at the time. He was appointed professor of surveying and geodesy at the Polytechnic in 1909, succeeding Max Rosenmund, who had died in 1908, and whose work had included surveying the Simplon Tunnel. This is presumably how surveying theodolite no. 18642 came to be in what was then the Geodetic Institute of the Polytechnic. E. Berchtold, assistant to Professor Bäschlin starting from 1921, describes in an article how the instruments played an important role at the Geodetic Institute and were well looked after. The Lötschberg theodolite was considered particularly “carefully guarded”. Nevertheless, he was allowed to clean, oil and readjust it – apparently a special experience for him – in 1921. 4
The construction of the Lötschberg tunnel was overshadowed by two major accidents. The hotel in Goppenstein where numerous engineers were staying was destroyed by an avalanche in February 1908. 12 people lost their lives. Then in July of the same year, 25 Italian miners died as a result of a debris avalanche. Construction work was then interrupted for 6 months. The tunnel’s breakthrough took place on 31 March 1911 following slightly altered routing, and Lötschberg tunnel was opened on 19 June 1913. The 14.6 km route was electrified throughout from the beginning.5
As with the target marker for the Simplon, choosing this object was easy: One thing we know about this instrument was that it was used during the surveying work for the Lötschberg tunnel. As material evidence, the theodolite tells of this historic event. Thanks to the Kern order book as well as several articles on the construction of the Lötschberg tunnel, the object can be classified quite accurately.
Photogrammetry and digitalisation
As already known from the other surveying instruments, this theodolite’s glasses, lenses and mirrors as well as its animated structures had to be added manually or created completely by hand. The photogrammetric capture of the attached rider level, the Zwicky level, was carried out separately.
Conclusion of the series on 3D digitisation
Today the twentieth and last article has been published. Since 17.05.2023, we have described a 3D digitised object in more detail every Wednesday. At the same time, we have also documented why we have chosen this object for 3D digitisation and in which context we use or would like to use the 3D model, for example for guided tours. We also described a few technical notes on the digitisation, for example if a lot of manual modelling was required due to reflections. For this part, we relied on the information provided by Thomas Erdin from the company ikonaut, who created the digitised models for us.
The project was an attempt to find out whether and how we can use 3D digitisation for the collection of scientific instruments and teaching aids. Overall, we draw a positive balance. The animations in particular offer great added value for teaching the instruments. Our next step is to consider whether 3D digitised objects from our collection could also be of interest for research and teaching. For this purpose, we are starting a follow-up project. Together with Prof. Norbert Hungerbühler from the Department of Mathematics at ETH Zurich and ikonaut, we are digitising mathematical models in 3D. These are plaster models created in the 19th century by the publishers Martin Schilling and Ludwig Brill 6. The goal of the project is to use the 3D model to measure the historical models and compare them with a computer-generated model.
Click here again for all blogposts on the 3D models: https://etheritage.ulapiluh.myhostpoint.ch/category/bestaende/3d-modell/
And here are the models on Sketchfab: https://sketchfab.com/ethlibrary