Geoid models in GeoCue are grid-based. The required file format is simply a rectangular grid of geoid undulation values, N, where h = H+N, with h representing the ellipsoid height and H the geoid height. The grid contains only undulation values. The grid points are required to be at regular geographic intervals in latitude and longitude. The grid file may have an optional header, followed by an array of single precision floating point values (4 bytes each). The first point of the array must represent the minimum latitude and longitude of coverage for the model. The second point is the same latitude, but for the next increment of longitude. The array proceeds likewise for as many columns as the grid covers in longitude and then row-wise for increasing latitude.
Read the full article: CueTip – Adding a New Geoid Model in GeoCue
To enable deprecated Geoid Models please seeing the following post: Enabling Deprecated Geoids