AUSGeoid98 data files contain a 2 minute grid of AUSGeoid98 data covering the Australian region, which you can use to interpolate geoid-ellipsoid separations for the positions required.You can use you
Aerial color orthophotography mosaic, with a spatial resolution of 50 cm/pixel, produced from the photogrammetric flight carried out in 2012 by the PNOA-Government of La Rioja in ECW and JPEG format.