At swisstopo, we have been photographing Switzerland from above since the mid-1920s. Several changes in equipment have made it possible to follow the technological evolution from black and white to colour, to add infrared information or to increase ground resolution. In 2005, the acquisition of aerial images entered the digital age.  

State-of-the-art airborne technology

Swisstopo uses a Leica Geosystems ADS100 camera to record its aerial images. Based on the push-broom method, this linear sensor scans a strip of the landscape while the aircraft moves and produces a single long image (covering a distance of more than 100 kilometres). This method requires fewer images than conventional frame cameras for covering the equivalent surface area. This means that the need to join images together is thus reduced to a minimum.

Each image strip is taken from three angles: directly from above, to the front and to the rear. These different angles of view enable us to produce a three-dimensional model of the landscape and measure the position and altitude of objects with great accuracy. This process is referred to as photogrammetric restitution. It allows swisstopo to generate and update a large amount of data, such as terrain models, 3D landscape models and national maps.

To ensure optimum coverage, images are recorded with a lateral overlap of at least 30 percent. To guarantee the best possible quality of our products, from 2017 onwards all photographs will be taken with a ground resolution of 10 centimetres on the Swiss central plateau, in the Jura and in the two main Alpine valleys (the Rhone downstream from Brig and the Rhine downstream from Chur). With significant differences in altitude, the more complex topography of the Alps limits this ground resolution to 25 centimetres.

Distribution of ground resolutions: 10 cm (blue) and 25 cm (green) - subject to change

To obtain these images, the aircraft flies over Switzerland from west to east or follows the axis of the valleys whenever the topography does not allow this. The aircraft flies at an altitude of around 2,400 metres above the ground in order to produce a resolution of 10 centimetres, and at around 6,000 metres above the ground for a resolution of 25 centimetres.

Photography by region

swisstopo periodically flies over and photographs Switzerland and Liechtenstein. Since 2008, one-third of the territory has been photographed each year according to a defined regional division. As of 2017, the country has been divided into 3 regions based on cantonal boundaries.

• Western region (6 cantons: GE, VD, NE, FR, JU, VS) - First acquisition 2017, next acquistion every three years.
• Central region (10 cantons: BE, BL, BS, SO, AG, LU, OW, NW, UR, TI) - First acquisition 2018, next acquistion every three years.
• Eastern region (10 cantons: SH, ZH, TG, SG, AI, AR, SZ, GL, ZG, GR) and the Principality of Liechtenstein - First acquisition 2019, next acquistion every three years.
   

Thanks to this regional division, municipalities and cantons are always in possession of complete data from the same flight year for their entire sovereign territory.