GPS·H allows GPS users to convert their ellipsoidal heights (h) in either NAD83(CSRS) or ITRF/WGS84 to orthometric heights H (heights above mean sea level) by applying at each location a geoid height N derived from a geoid model (or Height Transformation).
Depending on the application, either a geoid model (CGG2010 is the latest) or the HT2.0 "Height Transformation" can be used. Several GPS and GIS software packages can also read geoid models to produce orthometric heights.
Note: the online version currently can only apply the HT2.0 height transformation. The GPS·H software download comes with HT2.0 as a default but it can read other geoid models. The geoid models CGG2010 (the latest), CGG2005, CGG2000, GSD95 and GSD91 can all be downloaded here.