NOAA Technical Memorandum NOS NGS-58 [html
| pdf]
presents the guidelines for establishing GPS-derived Ellipsoidal
Heights (Standards: 2 cm and 5 cm) Version 4.3
DRAFT
Guidelines for Establishing GPS-derived Orthometric Heights
(Standards: 2 cm and 5 cm) are available. These DRAFT guidelines
address the establishment and densification of vertical control
networks through the use of GPS surveys and valid NAVD 88 orthometric
control. Comments are welcome. Please send your feedback to ngs.ngs.htmod@noaa.gov.