United States Geoid Model of 1999

Marius Lazar

September 02, 2026 12:50 Updated

The United States geoid models relate the difference between the GRS80 ellipsoid and the NAVD88 vertical datum..

The "GEOID99" vertical transform has the following parameters:

Parameter Name	Parameter String	Units
Path to directory containing grid files	path	String
File extension of grid files	extension	String

The path parameter can either be fully qualified or relative to the location of the data source file in which it is defined. The path string should not end with a slash character.

For more information, please consult the NGS Website.