DOUBLE PRECISION FUNCTION iau_EORS ( RNPB, S ) *+ * - - - - - - - - - * i a u _ E O R S * - - - - - - - - - * * Equation of the origins, given the classical NPB matrix and the * quantity s. * * This routine is part of the International Astronomical Union's * SOFA (Standards of Fundamental Astronomy) software collection. * * Status: support routine. * * Given: * RNPB d(3,3) classical nutation x precession x bias matrix * S d the quantity s (the CIO locator) in radians * * Returned: * iau_EORS d the equation of the origins in radians * * Notes: * * 1) The equation of the origins is the distance between the true * equinox and the celestial intermediate origin and, equivalently, * the difference between Earth rotation angle and Greenwich * apparent sidereal time (ERA-GST). It comprises the precession * (since J2000.0) in right ascension plus the equation of the * equinoxes (including the small correction terms). * * 2) The algorithm is from Wallace & Capitaine (2006). * * References: * * Capitaine, N. & Wallace, P.T., 2006, Astron.Astrophys. 450, 855 * * Wallace, P. & Capitaine, N., 2006, Astron.Astrophys. 459, 981 * * This revision: 2020 November 14 * * SOFA release 2021-01-25 * * Copyright (C) 2021 IAU SOFA Board. See notes at end. * *----------------------------------------------------------------------- IMPLICIT NONE DOUBLE PRECISION RNPB(3,3), S DOUBLE PRECISION X, AX, XS, YS, ZS, P, Q * - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - * Evaluate Wallace & Capitaine (2006) expression (16). X = RNPB(3,1) AX = X / ( 1D0 + RNPB(3,3) ) XS = 1D0 - AX*X YS = -AX*RNPB(3,2) ZS = -X P = RNPB(1,1)*XS + RNPB(1,2)*YS + RNPB(1,3)*ZS Q = RNPB(2,1)*XS + RNPB(2,2)*YS + RNPB(2,3)*ZS IF ( P.NE.0D0 .OR. Q.NE.0D0 ) THEN iau_EORS = S - ATAN2 ( Q, P ) ELSE iau_EORS = S END IF * 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