SUBROUTINE iau_C2T06A ( TTA, TTB, UTA, UTB, XP, YP, RC2T ) *+ * - - - - - - - - - - - * i a u _ C 2 T 0 6 A * - - - - - - - - - - - * * Form the celestial to terrestrial matrix given the date, the UT1 and * the polar motion, using the IAU 2006/2000A precession-nutation * model. * * This routine is part of the International Astronomical Union's * SOFA (Standards of Fundamental Astronomy) software collection. * * Status: support routine. * * Given: * 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 two arguments. 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 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. * * Called: * iau_C2I06A celestial-to-intermediate matrix, IAU 2006/2000A * 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.), 2004, IERS Conventions (2003), * IERS Technical Note No. 32, BKG * * This revision: 2023 April 16 * * SOFA release 2023-10-11 * * Copyright (C) 2023 IAU SOFA 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. CALL iau_C2I06A ( 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) 2023 * 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