Inertial and GPS
Inertial gives position, acceleration and velocity vector continuously. GPS gives position only unless speed is derived from position (inertial derives speed from acceleration). Both have some issues with respect to height - inertial has undamped errors which may require assistance from air data, GPS has to derive height from an earth centric smoothed ellipsoid. Would expect the kalman filter to be primarily blending air data height, and GPS position, with the base IRS model in order to continuously refine the IRS errors sources and for the enhanced IRS output to be the primary source for navigation.