Function lupnt::RotPrecessionNutation

Function Documentation

Mat3 lupnt::RotPrecessionNutation(Real t_tdb)

Returns the precession-nutation rotation matrix R_pn at epoch t_tdb, which rotates a vector from GCRF (ICRF-aligned, mean-equator-of-J2000) into the true-equator-and-equinox-of-date frame (CIRS-like intermediate frame), i.e. v_intermediate = R_pn * v_GCRF (IAU 2006/2000A precession-nutation, computed from the SOFA (X, Y, s) CIP coordinates via GetIauSofaData).

Used internally by GcrfToItrf/ItrfToGcrf (and by ComputeEopFromSpice, which inverts the same decomposition) as the first stage of the full GCRF<->ITRF rotation R_GcrfToItrf = R_po * R_s * R_pn.

Note

Astrodynamics Convention & Modeling Reference, Version 1.1, Page 34

Parameters:

t_tdb – Epoch [s, TDB since J2000]

Returns:

3x3 precession-nutation rotation matrix R_pn (dimensionless)