NOTE: The DRAFT Guidelines for Establishing GPS-Derived Orthometric Heights differ from NOAA Technical Memorandum NOS NGS-58: Guidelines for Establishing GPS-Derived Ellipsoid Heights (Standards: 2 cm and 5 cm). In November 1997, the National Geodetic Survey (NGS) published guidelines for performing GPS surveys that are intended to achieve ellipsoid height network accuracies of 5 cm at the 95 percent confidence level, as well as ellipsoid height local accuracies of 2 cm or 5 cm, also at the 95 percent confidence level (Zilkoski et al. 1997).

NGS developed the DRAFT Guidelines for Establishing GPS-Derived Orthometric Heights (2 cm and 5 cm) guidelines for performing GPS surveys that are intended to achieve orthometric height network accuracies of 5 cm at the 95 percent confidence level, as well as orthometric height local accuracies of 2 cm or 5 cm, also at the 95 percent confidence level. The DRAFT Guidelines for Establishing GPS-Derived Orthometric Heights (2 cm and 5 cm) were developed in partnership with Federal, state, and local government agencies, academia, and private geodetic surveyors.