Topography - Surveying - Geodesy

The original purpose of geodesy was to study and measure the general shape of the Earth, its rotation, its gravitational field and the various reference systems that can be used to find one's way around its surface. By extension, the geodesist is the person who provides known support points with coordinates for topographic work, the purpose of which is to considerably increase the density of this reference framework.

The purpose of topography is to describe and represent the shape of the Earth's surface locally. Topographers carry out surveys, either by measuring directly in the field (angle, distance or GNSS measurements; § 2.2 and 2.3.1 ), or by exploiting the metric properties of aerial or space stereoscopic images of the ground (photogrammetry).

Topometry is the set of geometric methods used to measure the relative positions of points. It is the topographer's basic toolbox.

The surveyor's work covers a wide range of complementary activities, from topography in all its forms to cartography (the art of representing topography in the best possible way in the form of maps, on screen or on paper), and all the technical and legal aspects of defining land ownership.

Important note: in Topography, Topometry and Geodesy, angles are expressed in degrees or gons (formerly called grades). We remind you of the correspondences with legal units:

• 1° = π/180 rad ;

• 1 gon = π/200 rad.