Approximate Altitude Computation in STK

The approximate altitude computation in STK uses the following formula for an oblate spheroid,

where R is the distance from the center of the oblate spheroid, R_e is the equatorial radius, f is the flattening factor and φ is the spherical latitude. The flattening factor is related to the equatorial and polar radii as

and to the eccentricity of an elliptical cross-section by

The nominal shape of the Earth is defined by the WGS-84 defining constants of