missing correction in Equation Of Equinoxes
The Equation Of Equinoxes adds the periodic nutation components to the
thus changing the GMST (mean) into GAST (apparent).
The equation involves a ΔΨ cos(ε₀) part. In the current version of
Orekit, the correction
part δΔΨ read in the EOP file is not included in the ΔΨ, which introduces an error in longitude.
Comparing ITRF computation from equinox paradigm and Non-Rotating Origin
shows this effect
to be the dominant error (about 1 milli arcsecond for IERS 2010 conventions). Of course, the
error disappears when EOP files are not available.
Looking in the SOFA manual examples also shows the correction should be
included, as part
of the code in section 5.2 "IAU 1976/1980/1982/1994, equinox based" reads:
* Equation of the equinoxes, including nutation correction. EE = iau_EQEQ94 ( DJMJD0, TT ) + DDP80 * COS ( EPSA )
(from redmine: issue id 150, created on 2013-10-01, closed on 2013-10-01)