### 2. Heights

Unless the ellipsoid is made to coincide with the geoid, separations between the surfaces vary, Figure C-5.

 Figure C-5Geocentric Earth Model

There are three heights at each point, Figure C-6:

• H: Orthometric height; from the geoid to the ground point; elevation determined by leveling from a benchmark
• N: Geoid height; from the ellipsoid to the geoid. Also known as the geoidal height.
• h: Geodetic height; from the ellipsoid to the ground point. Also known as the ellipsoidal height.
 Figure C-6Heights

The heights are related by Equation C-1.

 Equation C-1