A set of parameters and constants that defines a coordinate system, including its origin and orientation and scale, used for geodetic applications is known as which term?

• A. Horizontal Datum
• B. Vertical Datum
• C. Ellipsoid
• D. Geodetic Datum

Answer: (D)

In geodesy, a geodetic datum is the reference framework that defines a coordinate system by tying together the mathematical model of the Earth with real-world positions. It includes the origin, the orientation of the coordinate axes, and the scale or other transformation parameters that align the reference surface (the ellipsoid) with the Earth's surface. This makes it the comprehensive term for the system used in geodetic applications. The ellipsoid by itself is just a smooth surface model, not a full coordinate framework; a horizontal datum or vertical datum describes parts of the system (positions on the surface or elevations), but the full set of parameters that defines the coordinate system in a geodetic sense is the geodetic datum.