SUBROUTINE iau_C2IXYS ( X, Y, S, RC2I ) *+ * - - - - - - - - - - - * i a u _ C 2 I X Y S * - - - - - - - - - - - * * Form the celestial to intermediate-frame-of-date matrix given the CIP * X,Y and the CIO locator s. * * This routine is part of the International Astronomical Union's * SOFA (Standards of Fundamental Astronomy) software collection. * * Status: support routine. * * Given: * X,Y d Celestial Intermediate Pole (Note 1) * S d the CIO locator s (Note 2) * * Returned: * RC2I d(3,3) celestial-to-intermediate matrix (Note 3) * * Notes: * * 1) The Celestial Intermediate Pole coordinates are the x,y components * of the unit vector in the Geocentric Celestial Reference System. * * 2) The CIO locator s (in radians) positions the Celestial * Intermediate Origin on the equator of the CIP. * * 3) The matrix RC2I is the first stage in the transformation 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. * * Called: * iau_IR initialize r-matrix to identity * iau_RZ rotate around Z-axis * iau_RY rotate around Y-axis * * Reference: * * McCarthy, D. D., Petit, G. (eds.), IERS Conventions (2003), * IERS Technical Note No. 32, BKG (2004) * * This revision: 2006 October 10 * * Copyright (C) 2008 IAU SOFA Review Board. See notes at end. * *----------------------------------------------------------------------- IMPLICIT NONE DOUBLE PRECISION X, Y, S, RC2I(3,3) DOUBLE PRECISION R2, E, D * - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - * Obtain the spherical angles E and d. R2 = X*X+Y*Y IF ( R2.NE.0D0 ) THEN E = ATAN2 ( Y, X ) ELSE E = 0D0 END IF D = ATAN ( SQRT ( R2 / (1D0-R2) ) ) * Form the matrix. CALL iau_IR ( RC2I ) CALL iau_RZ ( E, RC2I ) CALL iau_RY ( D, RC2I ) CALL iau_RZ ( -(E+S), RC2I ) * 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