SUBROUTINE iau_XYS00A ( DATE1, DATE2, X, Y, S )
*+
* - - - - - - - - - - -
* i a u _ X Y S 0 0 A
* - - - - - - - - - - -
*
* For a given TT date, compute the X,Y coordinates of the Celestial
* Intermediate Pole and the quantity s, using the IAU 2000A precession-
* nutation model.
*
* This routine is part of the International Astronomical Union's
* SOFA (Standards of Fundamental Astronomy) software collection.
*
* Status: support routine.
*
* Given:
* DATE1,DATE2 d TT as a 2-part Julian Date (Note 1)
*
* Returned:
* X,Y d Celestial Intermediate Pole (Note 2)
* S d the quantity s (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
*
* 2450123.7D0 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 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 Celestial Intermediate Pole coordinates are the x,y components
* of the unit vector in the Geocentric Celestial Reference System.
*
* 3) The quantity s (in radians) positions the Celestial Ephemeris
* Origin on the equator of the CIP.
*
* 4) A faster, but slightly less accurate result (about 1 mas for X,Y),
* can be obtained by using instead the iau_XYS00B routine.
*
* Called:
* iau_PNM00A bias-precession-nutation matrix, IAU 2000A
* iau_BPN2XY extract CIP coordinates from b-p-n matrix
* iau_S00 the quantity s, given X,Y
*
* Reference:
*
* McCarthy, D. D., Petit, G. (eds.), IERS Conventions (2003),
* IERS Technical Note No. 32, BKG (2004)
*
* This revision: 2005 August 24
*
* Copyright (C) 2005 IAU SOFA Review Board. See notes at end.
*
*-----------------------------------------------------------------------
IMPLICIT NONE
DOUBLE PRECISION DATE1, DATE2, X, Y, S
DOUBLE PRECISION RBPN(3,3)
DOUBLE PRECISION iau_S00
* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
* Form the bias-precession-nutation matrix, IAU 2000A.
CALL iau_PNM00A ( DATE1, DATE2, RBPN )
* Extract X,Y.
CALL iau_BPN2XY ( RBPN, X, Y )
* Obtain s.
S = iau_S00 ( DATE1, DATE2, X, Y )
* Finished.
*+----------------------------------------------------------------------
*
* Copyright (C) 2005
* Standards Of Fundamental Astronomy Review Board
* of the International Astronomical Union.
*
* =====================
* SOFA Software License
* =====================
*
* NOTICE TO USER:
*
* BY USING THIS SOFTWARE YOU ACCEPT THE FOLLOWING TERMS AND CONDITIONS
* WHICH APPLY TO ITS USE.
*
* 1. The Software is owned by the IAU SOFA Review Board ("the Board").
*
* 2. The Software is made available free of charge for use by:
*
* a) private individuals for non-profit research; and
*
* b) non-profit educational, academic and research institutions.
*
* 3. Commercial use of the Software is specifically excluded from the
* terms and conditions of this license. Commercial use of the
* Software is subject to the prior written agreement of the Board on
* terms to be agreed.
*
* 4. The provision of any version of the Software under the terms and
* conditions specified herein does not imply that future versions
* will also be made available under the same terms and conditions.
*
* 5. The user may modify the Software for his/her own purposes. The
* user may distribute the modified software provided that the Board
* is informed and that a copy of the modified software is made
* available to the Board on request. All modifications made by the
* user shall be clearly identified to show how the modified software
* differs from the original Software, and the name(s) of the
* affected routine(s) shall be changed. The original SOFA Software
* License text must be present.
*
* 6. In any published work produced by the user and which includes
* results achieved by using the Software, the user shall acknowledge
* that the Software was used in producing the information contained
* in such publication.
*
* 7. The user may incorporate or embed the Software into other software
* products which he/she may then give away free of charge but not
* sell provided the user makes due acknowledgement of the use which
* he/she has made of the Software in creating such software
* products. Any redistribution of the Software in this way shall be
* made under the same terms and conditions under which the user
* received it from the SOFA Center.
*
* 8. The user shall not cause the Software to be brought into
* disrepute, either by misuse, or use for inappropriate tasks, or by
* inappropriate modification.
*
* 9. The Software is provided to the user "as is" and the Board makes
* no warranty as to its use or performance. The Board does not and
* cannot warrant the performance or results which the user may
* obtain by using the Software. The Board makes no warranties,
* express or implied, as to non-infringement of third party rights,
* merchantability, or fitness for any particular purpose. In no
* event will the Board be liable to the user for any consequential,
* incidental, or special damages, including any lost profits or lost
* savings, even if a Board representative has been advised of such
* damages, or for any claim by any third party.
*
* Correspondence concerning SOFA software should be addressed as
* follows:
*
* Internet email: sofa@rl.ac.uk
* Postal address: IAU SOFA Center
* Rutherford Appleton Laboratory
* Chilton, Didcot, Oxon OX11 0QX
* United Kingdom
*
*
*-----------------------------------------------------------------------
END