Acquisition of survey data

In order for a building, a municipal boundary or the edge of a forest to be shown on the map, points must be surveyed and their coordinates calculated. Many methods and procedures are available to achieve this task.

The oldest land survey method makes use of direct measurements in the field. The most common survey instrument is the electronic theodolite or “total station”, which measures angles and distances from which the coordinates and heights of the surveyed objects can be computed. Modern digital instruments carry out some of these computations directly in the field and store the results; these can then be downloaded for further processing in the office computer system.

Levelling is a very precise method of determining height differences. The levelling instrument is set up with a horizontal line of sight between two vertical levelling staves. The difference between the readings on each staff gives the height difference between the two staff stations.

Positioning systems using signals from satellites are best known from their use in navigation systems in cars, aircraft and ships or even as handheld devices for hikers. But also cadastral surveying can nowadays not be imagined without it! How do they work? Navigation satellites orbit the earth and continuously emit signals which can be picked up by special receivers. From these signals, distances can be determined and thus the position of the receiver be calculated. With specialised measurement and computational methods, or simply by using the automated Swiss GNSS network (AGNES), coordinates and heights can be determined in seconds to an accuracy of a few centimetres.

The following GNSS are in operation or under development: GPS (USA), GLONASS (Russia), GALILEO (Europe, planned to be operational beginning in 2013) and COMPASS (China, planned to be operational beginning in 2015).

Photogrammetry is a surveying method also used in cadastral surveying. The terrain is photographed systematically from aircraft equipped with a special camera taking series of photographs. Using a special workstation or stereoscopic plotting instrument the images are optically rectified and joined as pairs to form a three-dimensional model in which mountains tower up towards the observer and ravines appear to gape open. From this model, objects can be surveyed in 3D and contour lines can be plotted. Digital cameras and modern software are now also being applied in photogrammetry.

This new surveying method is also being carried out from aircraft. An air-borne laser scans the terrain and determines the distance to the terrain by its position and the elapsed time. Information can thus be gained about the topography and structure of the terrain.