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 measuring them. These methods, … See more

In geodetic coordinates, Earth's surface is approximated by an ellipsoid, and locations near the surface are described in terms of 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

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

Horizontal datum
The horizontal datum is the model used to measure positions on Earth. A specific point can have substantially different coordinates, depending on the datum used to make the measurement. There are hundreds of local … 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 … See more

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