EGM96 EGM96 (Earth Gravitational Model 1996) is a geopotential model of the Earth consisting of spherical harmonic coefficients complete to degree and order 360. See https://en.wikipedia.org/wiki/EGM96 NAVD88 North American Vertical Datum of 1988 Originally from CUAHSI HIS ODM CV. See http://his.cuahsi.org/mastercvreg/edit_cv11.aspx?tbl=VerticalDatumCV. AHD Australian Height Datum. Height datum used for standardised elevations across Australia. The datum surface is defined as that which passes through mean sea level at the 30 specified tide gauges and through points at zero AHD height vertically below the other basic junction points. See http://www.ga.gov.au/scientific-topics/positioning-navigation/geodesy/geodetic-datums/australian-height-datum-ahd MSL Mean Sea Level Originally from CUAHSI HIS ODM CV. See http://his.cuahsi.org/mastercvreg/edit_cv11.aspx?tbl=VerticalDatumCV. NGVD29 National Geodetic Vertical Datum of 1929 Originally from CUAHSI HIS ODM CV. See http://his.cuahsi.org/mastercvreg/edit_cv11.aspx?tbl=VerticalDatumCV. Unknown The vertical datum is unknown Originally from CUAHSI HIS ODM CV. See http://his.cuahsi.org/mastercvreg/edit_cv11.aspx?tbl=VerticalDatumCV. ODM2 Elevation Datum Controlled Vocabulary ODM2 Working Group A vocabulary for describing vertical datums. Vertical datums are used in ODM2 to specify the origin for elevations assocated with SamplingFeatures.