Earth is not actually round (spherical), so an ellipsoid is considered a simple geoid approximation and used as a reference model (datum) to calculate altitude, based on position. World Geodesic System 1984 (WGS84) is a better worldwide reference.
Earth is not perfectly round (spherical), so an ellipsoid is considered a simple geoid approximation that can be used as a reference model (datum) to account for spheroid distortions in the calculation of altitude (vertical height), based on position. The World Geodesic System 1984 (WGS84) is considered a better worldwide reference. The WGS84 mathematical ellipsoid has been used by GPS since January 1987.
- Ellipsoid is a mathematical shape obtained by rotating an ellipse around its minor axis (a flattened sphere). It is commonly referred to as a spheroid.
- Ellipsoid height, also referred as geodetic height, is the difference between the ellipsoid and a point on the Earth’s surface (not the same as altitude over the sea level).
- Geoid height is the offset value between the reference geoid and the ellipsoid models.
- Orthometric height or Altitude is the distance between a point on the Earth’s surface and the geoid. Since the geoid represents the Mean Sea Level, this is the value most antenna installers are interested about.
GPS/GNSS receivers use a smoothed model of sea level to calculate elevation. The model is called a reference ellipsoid. This means that the elevation reading from the GPS/GNSS receiver is not the vertical distance from true sea level, but rather the distance from the reference ellipsoid.