The spherical nature of Earth was known by the ancient Greeks, who also developed the concepts of latitude and longitude, and the first astronomical methods for … See more

In geodetic coordinates, Earth's surface is approximated by an ellipsoid, and locations near the surface are described in terms of geodetic latitude ($${\displaystyle \phi }$$), longitude ($${\displaystyle \lambda }$$), and ellipsoidal height ($${\displaystyle h}$$ See more

A geodetic reference datum is a known and constant surface which is used to describe the location of unknown points on Earth. Since … See more

• Axes conventions
• ECEF
• ECI (coordinates)
• Engineering datum See more

Horizontal datum
A horizontal datum is a model used to precisely measure positions on Earth; it is thus a crucial component of any spatial reference system See more

The difference in co-ordinates between datums is commonly referred to as datum shift. The datum shift between two particular datums can vary from one place to another within one country or region, and can be anything from zero to hundreds of meters … See more

The Earth's tectonic plates move relative to one another in different directions at speeds on the order of 50 to 100 mm (2.0 to 3.9 in) per year. Therefore, locations on different plates are in motion relative to one another. For example, the longitudinal difference between … See more