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.