c2t00a¶
- erfa.c2t00a(tta, ttb, uta, utb, xp, yp)[source]¶
Form the celestial to terrestrial matrix given the date, the UT1 and the polar motion, using the IAU 2000A precession-nutation model.
- Parameters:
- ttadouble array
- ttbdouble array
- utadouble array
- utbdouble array
- xpdouble array
- ypdouble array
- Returns:
- rc2tdouble array
Notes
Wraps ERFA function
eraC2t00a
. The ERFA documentation is:- - - - - - - - - - e r a C 2 t 0 0 a - - - - - - - - - - Form the celestial to terrestrial matrix given the date, the UT1 and the polar motion, using the IAU 2000A precession-nutation model. Given: tta,ttb double TT as a 2-part Julian Date (Note 1) uta,utb double UT1 as a 2-part Julian Date (Note 1) xp,yp double CIP coordinates (radians, Note 2) Returned: rc2t double[3][3] celestial-to-terrestrial matrix (Note 3) Notes: 1) The TT and UT1 dates tta+ttb and uta+utb are Julian Dates, apportioned in any convenient way between the arguments uta and utb. For example, JD(UT1)=2450123.7 could be expressed in any of these ways, among others: uta utb 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 and MJD methods are good compromises between resolution and convenience. In the case of uta,utb, the date & time method is best matched to the Earth rotation angle algorithm used: maximum precision is delivered when the uta argument is for 0hrs UT1 on the day in question and the utb argument lies in the range 0 to 1, or vice versa. 2) The arguments xp and yp are the coordinates (in radians) of the Celestial Intermediate Pole with respect to the International Terrestrial Reference System (see IERS Conventions 2003), measured along the meridians 0 and 90 deg west respectively. 3) The matrix rc2t transforms 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), RC2I is the celestial-to-intermediate matrix, ERA is the Earth rotation angle and RPOM is the polar motion matrix. 4) A faster, but slightly less accurate, result (about 1 mas) can be obtained by using instead the eraC2t00b function. Called: eraC2i00a celestial-to-intermediate matrix, IAU 2000A eraEra00 Earth rotation angle, IAU 2000 eraSp00 the TIO locator s', IERS 2000 eraPom00 polar motion matrix eraC2tcio form CIO-based celestial-to-terrestrial matrix Reference: 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.