DOUBLE PRECISION FUNCTION iau_S00B ( DATE1, DATE2 )
*+
* - - - - - - - - -
* i a u _ S 0 0 B
* - - - - - - - - -
*
* The CIO locator s, positioning the Celestial Intermediate Origin on
* the equator of the Celestial Intermediate Pole, using the IAU 2000B
* 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:
* iau_S00B d the CIO locator s in radians (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 CIO locator s is the difference between the right ascensions
* of the same point in two systems. The two systems are the GCRS
* and the CIP,CIO, and the point is the ascending node of the
* CIP equator. The CIO locator s remains a small fraction of
* 1 arcsecond throughout 1900-2100.
*
* 3) The series used to compute s is in fact for s+XY/2, where X and Y
* are the x and y components of the CIP unit vector; this series is
* more compact than a direct series for s would be. The present
* routine uses the IAU 2000B truncated nutation model when
* predicting the CIP position. The routine iau_S00A uses instead
* the full IAU 2000A model, but with no significant increase in
* accuracy and at some cost in speed.
*
* Called:
* iau_PNM00B classical NPB matrix, IAU 2000B
* iau_BNP2XY extract CIP X,Y from the BPN matrix
* iau_S00 the CIO locator s, given X,Y, IAU 2000A
*
* References:
*
* Capitaine, N., Chapront, J., Lambert, S. and Wallace, P.,
* "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: 2010 January 18
*
* SOFA release 2021-05-12
*
* Copyright (C) 2021 IAU SOFA Board. See notes at end.
*
*-----------------------------------------------------------------------
IMPLICIT NONE
DOUBLE PRECISION DATE1, DATE2
DOUBLE PRECISION RBPN(3,3), X, Y
DOUBLE PRECISION iau_S00
* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
* Bias-precession-nutation-matrix, IAU 2000B.
CALL iau_PNM00B ( DATE1, DATE2, RBPN )
* Extract the CIP coordinates.
CALL iau_BPN2XY ( RBPN, X, Y )
* Compute the CIO locator s, given the CIP coordinates.
iau_S00B = iau_S00 ( DATE1, DATE2, X, Y )
* Finished.
*+----------------------------------------------------------------------
*
* Copyright (C) 2021
* Standards Of Fundamental Astronomy Board
* of the International Astronomical Union.
*
* =====================
* SOFA Software License
* =====================
*
* NOTICE TO USER:
*
* BY USING THIS SOFTWARE YOU ACCEPT THE FOLLOWING SIX TERMS AND
* CONDITIONS WHICH APPLY TO ITS USE.
*
* 1. The Software is owned by the IAU SOFA Board ("SOFA").
*
* 2. Permission is granted to anyone to use the SOFA software for any
* purpose, including commercial applications, free of charge and
* without payment of royalties, subject to the conditions and
* restrictions listed below.
*
* 3. You (the user) may copy and distribute SOFA source code to others,
* and use and adapt its code and algorithms in your own software,
* on a world-wide, royalty-free basis. That portion of your
* distribution that does not consist of intact and unchanged copies
* of SOFA source code files is a "derived work" that must comply
* with the following requirements:
*
* a) Your work shall be marked or carry a statement that it
* (i) uses routines and computations derived by you from
* software provided by SOFA under license to you; and
* (ii) does not itself constitute software provided by and/or
* endorsed by SOFA.
*
* b) The source code of your derived work must contain descriptions
* of how the derived work is based upon, contains and/or differs
* from the original SOFA software.
*
* c) The names of all routines in your derived work shall not
* include the prefix "iau" or "sofa" or trivial modifications
* thereof such as changes of case.
*
* d) The origin of the SOFA components of your derived work must
* not be misrepresented; you must not claim that you wrote the
* original software, nor file a patent application for SOFA
* software or algorithms embedded in the SOFA software.
*
* e) These requirements must be reproduced intact in any source
* distribution and shall apply to anyone to whom you have
* granted a further right to modify the source code of your
* derived work.
*
* Note that, as originally distributed, the SOFA software is
* intended to be a definitive implementation of the IAU standards,
* and consequently third-party modifications are discouraged. All
* variations, no matter how minor, must be explicitly marked as
* such, as explained above.
*
* 4. You shall not cause the SOFA software to be brought into
* disrepute, either by misuse, or use for inappropriate tasks, or
* by inappropriate modification.
*
* 5. The SOFA software is provided "as is" and SOFA makes no warranty
* as to its use or performance. SOFA does not and cannot warrant
* the performance or results which the user may obtain by using the
* SOFA software. SOFA 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 SOFA be
* liable to the user for any consequential, incidental, or special
* damages, including any lost profits or lost savings, even if a
* SOFA representative has been advised of such damages, or for any
* claim by any third party.
*
* 6. The provision of any version of the SOFA 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.
*
* In any published work or commercial product which uses the SOFA
* software directly, acknowledgement (see www.iausofa.org) is
* appreciated.
*
* Correspondence concerning SOFA software should be addressed as
* follows:
*
* By email: sofa@ukho.gov.uk
* By post: IAU SOFA Center
* HM Nautical Almanac Office
* UK Hydrographic Office
* Admiralty Way, Taunton
* Somerset, TA1 2DN
* United Kingdom
*
*-----------------------------------------------------------------------
END