SUBROUTINE iau_C2T00A ( TTA, TTB, UTA, UTB, XP, YP, RC2T )
*+
* - - - - - - - - - - -
* i a u _ 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 nutation model.
*
* This routine is part of the International Astronomical Union's
* SOFA (Standards of Fundamental Astronomy) software collection.
*
* Status: support routine.
*
* Given:
* TTA,TTB d TT as a 2-part Julian Date (Note 1)
* UTA,UTB d UT1 as a 2-part Julian Date (Note 1)
* XP,YP d coordinates of the pole (radians, Note 2)
*
* Returned:
* RC2T d(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
*
* 2450123.7D0 0D0 (JD method)
* 2451545D0 -1421.3D0 (J2000 method)
* 2400000.5D0 50123.2D0 (MJD method)
* 2450123.5D0 0.2D0 (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 accuracy (or, at least, minimum noise) 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) 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 to 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 iau_C2T00B routine.
*
* Called:
* iau_C2I00A celestial-to-intermediate matrix, IAU 2000A
* iau_ERA00 Earth rotation angle, IAU 2000
* iau_SP00 the TIO locator s', IERS 2000
* iau_POM00 polar motion matrix
* iau_C2TCIO 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: 2009 April 1
*
* Copyright (C) 2008 IAU SOFA Review Board. See notes at end.
*
*-----------------------------------------------------------------------
IMPLICIT NONE
DOUBLE PRECISION TTA, TTB, UTA, UTB, XP, YP, RC2T(3,3)
DOUBLE PRECISION RC2I(3,3), ERA, SP, RPOM(3,3)
DOUBLE PRECISION iau_ERA00, iau_SP00
* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
* Form the celestial-to-intermediate matrix for this TT (IAU 2000A).
CALL iau_C2I00A ( TTA, TTB, RC2I )
* Predict the Earth rotation angle for this UT1.
ERA = iau_ERA00 ( UTA, UTB )
* Estimate s'.
SP = iau_SP00 ( TTA, TTB )
* Form the polar motion matrix.
CALL iau_POM00 ( XP, YP, SP, RPOM )
* Combine to form the celestial-to-terrestrial matrix.
CALL iau_C2TCIO ( RC2I, ERA, RPOM, RC2T )
* Finished.
*+-----------------------------------------------------------------------
*
* Copyright (C) 2008
* Standards Of Fundamental Astronomy Review Board
* of the International Astronomical Union.
*
* =====================
* SOFA Software License
* =====================
*
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*
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*
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*
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*
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*-----------------------------------------------------------------------
END