Ohio State University Geoid Model

The Ohio State University geoid model of 1991 (OSU91a)) is a global geoid model that transforms height values between the WGS84 ellipsoid and a geoid surface that is “closely associated” with mean sea level. The model data exist in a single binary file consisting of a 15-minute grid of elevation difference values between the two surfaces. The elevation differences at non-grid point locations are interpolated. This academic model was used as a base for most NGA geoid offset defintions.

The "OSU91a" vertical transform has the following parameters:

The path parameter can either be fully qualified or relative to the location of the data source file in which it is defined. The path string should not end with a slash character.