Vertical datum

• Reference surface for vertical positioning (altitude)

Gravity-related (geoidal) vertical coordinate system

• Vertical datums that use a geoid as a reference surface
• Used for orthometric height

Example

• NAVD88 (North American Vertical Datum of 1988)

Spheroidal (ellipsoidal) vertical coordinate system

• Used for ellipsoidal height

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Geoid, Orthometric height, Ellipsoidal height