Function lupnt::RotSideralMotion

Function Documentation

Mat3 lupnt::RotSideralMotion(Real t_tdb)

Returns the sidereal-motion (Earth-rotation) rotation matrix R_s at epoch t_tdb, which rotates a vector from the true-equator-and-equinox-of-date (intermediate) frame into the Earth-fixed (pseudo-ITRF, pre-polar-motion) frame by the Earth Rotation Angle (ERA) about the z-axis, i.e. v_pseudo_itrf = R_s * v_intermediate.

If InitFrameConversionFromSpice has fitted a SPICE-derived EOP model (see ComputeEopFromSpice) covering t_tdb, the fitted UT1-UTC is used in place of the loaded IERS EOP table.

Used internally by GcrfToItrf/ItrfToGcrf as the second stage of R_GcrfToItrf = R_po * R_s * R_pn. If InitFrameConversionFromSpice has fitted a SPICE-derived EOP model covering t_tdb, the fitted UT1-UTC is used in place of the loaded IERS EOP table when computing UT1 (and hence the ERA).

Note

Astrodynamics Convention & Modeling Reference, Version 1.1, Page 35

Parameters:

t_tdb – Epoch [s, TDB since J2000]

Returns:

3x3 sidereal-motion rotation matrix R_s (dimensionless)