DOUBLE PRECISION FUNCTION iau_S00A ( DATE1, DATE2 ) *+ * - - - - - - - - - * i a u _ S 0 0 A * - - - - - - - - - * * The CIO locator s, positioning the Celestial Intermediate Origin on * the equator of the Celestial Intermediate Pole, 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: * iau_S00A 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 full IAU 2000A nutation model when predicting the * CIP position. Faster results, with no significant loss of * accuracy, can be obtained via the routine iau_S00B, which uses * instead the IAU 2000B truncated model. * * Called: * iau_PNM00A classical NPB matrix, IAU 2000A * 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 2013-12-02 * * Copyright (C) 2013 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 2000A. CALL iau_PNM00A ( DATE1, DATE2, RBPN ) * Extract the CIP coordinates. CALL iau_BPN2XY ( RBPN, X, Y ) * Compute the CIO locator s, given the CIP coordinates. iau_S00A = iau_S00 ( DATE1, DATE2, X, Y ) * Finished. *+---------------------------------------------------------------------- * * Copyright (C) 2013 * 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