c2i00a¶
- erfa.c2i00a(date1, date2)[source]¶
Form the celestial-to-intermediate matrix for a given date using the IAU 2000A precession-nutation model.
- Parameters:
- date1double array
- date2double array
- Returns:
- rc2idouble array
Notes
Wraps ERFA function
eraC2i00a
. The ERFA documentation is:- - - - - - - - - - e r a C 2 i 0 0 a - - - - - - - - - - Form the celestial-to-intermediate matrix for a given date using the IAU 2000A precession-nutation model. Given: date1,date2 double TT as a 2-part Julian Date (Note 1) Returned: rc2i double[3][3] celestial-to-intermediate matrix (Note 2) Notes: 1) The TT date date1+date2 is a Julian Date, apportioned in any convenient way between the two arguments. For example, JD(TT)=2450123.7 could be expressed in any of these ways, among others: date1 date2 2450123.7 0.0 (JD method) 2451545.0 -1421.3 (J2000 method) 2400000.5 50123.2 (MJD method) 2450123.5 0.2 (date & time method) The JD method is the most natural and convenient to use in cases where the loss of several decimal digits of resolution is acceptable. The J2000 method is best matched to the way the argument is handled internally and will deliver the optimum resolution. The MJD method and the date & time methods are both good compromises between resolution and convenience. 2) The matrix rc2i is the first stage in the transformation from celestial to terrestrial coordinates: [TRS] = RPOM * R_3(ERA) * rc2i * [CRS] = rc2t * [CRS] where [CRS] is a vector in the Geocentric Celestial Reference System and [TRS] is a vector in the International Terrestrial Reference System (see IERS Conventions 2003), ERA is the Earth Rotation Angle and RPOM is the polar motion matrix. 3) A faster, but slightly less accurate, result (about 1 mas) can be obtained by using instead the eraC2i00b function. Called: eraPnm00a classical NPB matrix, IAU 2000A eraC2ibpn celestial-to-intermediate matrix, given NPB matrix References: "Expressions for the Celestial Intermediate Pole and Celestial Ephemeris Origin consistent with the IAU 2000A precession- nutation model", Astron.Astrophys. 400, 1145-1154 (2003) n.b. The celestial ephemeris origin (CEO) was renamed "celestial intermediate origin" (CIO) by IAU 2006 Resolution 2. McCarthy, D. D., Petit, G. (eds.), IERS Conventions (2003), IERS Technical Note No. 32, BKG (2004) This revision: 2021 May 11 Copyright (C) 2013-2023, NumFOCUS Foundation. Derived, with permission, from the SOFA library. See notes at end of file.