- Hydrographic Service
- Geodesy and Tides
Coordinate systems that are the horizontal and/or the vertical reference for geographic data are termed Coordinate Reference Systems (CRS). They are deduced from models for the surface of the earth, or a part of it.
Geometrical computations always take place within in a coordinate system. The choice of the system influences computations of positions, lines and areas. The horizontal CRS is also called the geodetic datum, and the vertical CRS for depths at sea the chart date.