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The long road to the topographical landscape model TLM

In December 2019, the development of the topographical landscape model (TLM) was officially completed. A look back to the early days of digitalisation at swisstopo in the 1960s shows how deeply rooted this achievement is in long-term efforts.

13.05.2020 | frf

Virtual representation of the old town of Bern, seen from the air
Bern, modelled by the TLM

Mountains, valleys, rivers, houses, bridges, roads, forests – Switzerland is shaped by innumerable features. The challenge that swisstopo had to overcome with the topographical landscape model (TLM) was just as great – each feature within this model that characterises the country’s landscape has a three-dimensional digital equivalent. Millions of features are entered into the database which, in turn, serves as the basis for producing national maps.

Planning for this extensive collection of geographical data on Switzerland began in 1999, with the development of the model commencing in 2008. swisstopo celebrated the conclusion of the TLM’s development in December 2019.

The first electronic computers at swisstopo

The conclusion of the TLM development is one of the latest milestones in terms of digitalisation at swisstopo. However, if you take a look back at the history of the Office of Topography, you will see that computer-aided processes have been employed by the Office for a good 60 years now. The TLM can also be seen in the context of this long-term development.

In the course of the 1960s, “automation”, as the delegation of calculations to electronic computers was called at the time, found its way into the world of national topography. In 1967 and 1969, the geodesy department put its first electronic desktop computers into operation with the Wanderer Conti and the Hewpack 9 100 A respectively, replacing analogue technologies such as logarithms, tables for trigonometric functions and mechanical calculators.

Product picture of the electronic desktop calculator Hewpack 9100 A, manufactured in the late 1960s
Hewpack 9100 A, the second desktop computer to be introduced at swisstopo.

The Hewpack 9100 A in particular opened up new horizons: in 1972, geodesist and later swisstopo Director Erich Gubler, a pioneer in digitalisation at swisstopo, stated that the computer was able to store 19 twelve-digit numbers, “calculate all trigonometric functions with one press of a button” and perform 500 additions per second.

The major time savings gained thanks to the electronic desktop computers accounted for their active use: “This has led to this machine being used virtually all day in the winter months. It’s not uncommon for it to be moved from one office to another three times in a day,” said Gubler.

The fact that the electronic computer always performed accurate calculations also fascinated geodesists. But this didn’t mean that errors were a thing of the past. Whilst it is true that they rarely occurred when performing calculations, they did arise when entering figures and programming the machines: “The computer really is very stupid, […] but it follows the commands of the programmer very closely and at an incredible speed.” This is how Erich Gubler described the relationship between humans and computers in 1972 – an outlook that has virtually always remained relevant to this day.

Man-sized computer with magnetic tapes as data storage
Central processing unit of the IBM 360 model 50 of the RZ EMD

Data transfer by post

The two desktop computers reached their performance limits in the complex compensation calculations of triangulation networks. This meant that the Office of Topography soon required greater computing power in the early days of digitalisation.

The Swiss Federal Military Department’s data centre (RZ EMD) offered the Office's engineers the capacity they needed. It could store up to 130,000 ten-digit values and perform approximately one million additions a second. However, the Office's computers were not linked to the EMD’s mainframe computer. The results gained with the help of the desktop computer had to be keyed in by hand and were transferred to punch cards, which were ultimately fed into the EMD computer.

The punch cards were transferred to the RZ EMD and the calculation results were sent to the Office of Topography by post, which meant a delay of two days for each arithmetic step. It was not until the end of the 1970s that the Office was able to link its first own mainframe computer, the PRIME 400, to the RZ EMD via modem.

Virtual representation of the city of Neuchâtel, oblique view from above
The centre of Neuchâtel in the TLM visualisation of the federal geoportal

TLM: a major step towards digitalisation

A look back at the early days of digitalisation at swisstopo shows that the TLM is the continuation of a process of development that began almost 60 years before with a desktop computing machine. After the first steps in geodesy, digital models based on the 1:25 000 national map followed in the 1980s and 1990s when the DHM25 height model and the VECTOR25 landscape model made their debut. The drawback of map-based models like this is that they have to take care of the simplification (generalisation) of the spatial conditions from the topographic maps. Generalisation is necessary when it comes to maps in order to guarantee their readability and interpretability.

The development and updating of the TLM since June 2008 represents a fundamental change in the production processes at swisstopo. Unlike before, digital models are no longer based on national maps, but the national maps are based on the digital model – the TLM. In contrast to its map-based predecessors, this is produced directly on the basis of aerial images, making it possible to develop a three-dimensional, precise and extremely detailed landscape model like the TLM. It includes more than 25 million features; the clearly distinguishable ones among them, such as houses or streets, are accurately portrayed right down to decimetre level.

The TLM is a highlight in terms of digitalisation at swisstopo. However, developments over the last 60 years show that the Office is constantly optimising the production and provision of geodata. It is expected that swisstopo will take further steps in digitisation which are virtually impossible to predict today.

Federal Office of Topography swisstopo Seftigenstrasse 264
P.O. Box
3084 Wabern
+41 58 469 01 11


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Infodesk history

Federal Office of Topography swisstopo

Seftigenstrasse 264
P.O. Box
3084 Wabern


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