SUBROUTINE iau_C2TXY ( TTA, TTB, UTA, UTB, X, Y, XP, YP, RC2T ) *+ * - - - - - - - - - - * i a u _ C 2 T X Y * - - - - - - - - - - * * Form the celestial to terrestrial matrix given the date, the UT1, the * CIP coordinates and the polar motion. IAU 2000. * * 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) * X,Y d Celestial Intermediate Pole (Note 2) * XP,YP d coordinates of the pole (radians, Note 3) * * Returned: * RC2T d(3,3) celestial-to-terrestrial matrix (Note 4) * * Notes: * * 1) The TT and UT1 dates TTA+TTB and UTA+UTB are Julian Dates, * apportioned in any convenient way between the arguments UTA and * UTB. 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) The Celestial Intermediate Pole coordinates are the x,y components * of the unit vector in the Geocentric Celestial Reference System. * * 3) 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 to 0 and 90 deg west respectively. * * 4) 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), ERA is the Earth * Rotation Angle and RPOM is the polar motion matrix. * * 5) Although its name does not include "00", this routine is in fact * specific to the IAU 2000 models. * * Called: * iau_C2IXY celestial-to-intermediate matrix, given X,Y * 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.), IERS Conventions (2003), * IERS Technical Note No. 32, BKG (2004) * * This revision: 2009 April 1 * * Copyright (C) 2008 IAU SOFA Review Board. See notes at end. * *----------------------------------------------------------------------- IMPLICIT NONE DOUBLE PRECISION TTA, TTB, UTA, UTB, X, Y, 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_C2IXY ( TTA, TTB, X, Y, 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) 2008 * 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. 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 adapt the SOFA software and its * algorithms for your own purposes and you may copy and distribute * a resulting "derived work" to others on a world-wide, royalty-free * basis, provided that the derived work complies 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 contain * software provided by SOFA or software that has been distributed * by or endorsed by SOFA. * * b) The source code of your derived work must contain descriptions * of how the derived work is based upon and/or differs from the * original SOFA software. * * c) The name(s) of all routine(s) that you distribute shall differ * from the SOFA names, even when the SOFA content has not been * otherwise changed. * * d) The routine-naming prefix "iau" shall not be used. * * e) 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. * * f) 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. * * 4. In any published work or commercial products which includes * results achieved by using the SOFA software, you shall acknowledge * that the SOFA software was used in obtaining those results. * * 5. You shall not cause the SOFA software to be brought into * disrepute, either by misuse, or use for inappropriate tasks, or by * inappropriate modification. * * 6. The SOFA software is provided "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 SOFA 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. * * 7. 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. * * 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