This document describes in a cookbook-fashion how to obtain geoid height at a given location on the Earth from spherical harmonic coefficients of a gravity model. The document is intended to aid ``the uninitiated oceanographer'' (Victor Zlotnicki, personal communication) in constructing geoid undulations relative to a given reference ellipsoid, defined by semi-major axis and flattening parameter, to be used with satellite altimetry products.
It is clearly beyond the scope of this cookbook to explain how certain formulas are developed from first principles and why the implicit approximations are appropriate. The interested reader is referred to standard textbooks such as Heiskanen and Moritz (1967) or Torge (1991)--where, incidently, all of the formulas stem from that are presented here.