Geodetic frame for Elevation/Azimuth calculations

[gwbres]

Could you please remind me what Frame I should use as a back up, to be able to resolve Elevation/Azimuth/Slant at all times ? (ie., backup geodetic frame).

My current implementation is to prefer ITRF93 if we can fully define and retrieve it (requires internet access once a day).
And I hesite between IAU_EARTH_FRAME and EARTH_J2000 as the other "never failling / less precise" option

[ChristopherRabotin]

Of course! You should use the IAU EARTH FRAME for the long term and lower precision frame for AzElRange.

If you want a few months of predictions of the high fidelity frame, you can also download the EOP prediction : https://naif.jpl.nasa.gov/pub/naif/generic_kernels/pck/earth_200101_990827_predict.bpc. I forgot that file existed until recently, but we started using it. You'll find the details on this dataset here: https://naif.jpl.nasa.gov/pub/naif/generic_kernels/pck/earth_200101_990827_predict.cmt.