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 quantity 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 quantity 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 quantity s (in radians) positions the Celestial Ephemeris * 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 2000), 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., IERS Conventions 2000, Chapter 5 (2002). * * This revision: 2002 November 9 * * Copyright (C) 2003 IAU SOFA Review Board. See notes at end. * *----------------------------------------------------------------------- IMPLICIT NONE DOUBLE PRECISION X, Y, S, RC2I(3,3) DOUBLE PRECISION E, D * - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - * Obtain the spherical angles E and d. IF ( X.NE.0D0 .OR. Y.NE.0D0 ) THEN E = ATAN2 ( Y, X ) ELSE E = 0D0 END IF D = ATAN ( SQRT((X*X+Y*Y) / (1D0-(X*X+Y*Y))) ) * 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) 2003 * 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. The Software is made available free of charge for use by: * * a) private individuals for non-profit research; and * * b) non-profit educational, academic and research institutions. * * 3. Commercial use of the Software is specifically excluded from the * terms and conditions of this license. Commercial use of the * Software is subject to the prior written agreement of the Board on * terms to be agreed. * * 4. The provision of any version of the 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. * * 5. The user may modify the Software for his/her own purposes. The * user may distribute the modified software provided that the Board * is informed and that a copy of the modified software is made * available to the Board on request. All modifications made by the * user shall be clearly identified to show how the modified software * differs from the original Software, and the name(s) of the * affected routine(s) shall be changed. The original SOFA Software * License text must be present. * * 6. In any published work produced by the user and which includes * results achieved by using the Software, the user shall acknowledge * that the Software was used in producing the information contained * in such publication. * * 7. The user may incorporate or embed the Software into other software * products which he/she may then give away free of charge but not * sell provided the user makes due acknowledgement of the use which * he/she has made of the Software in creating such software * products. Any redistribution of the Software in this way shall be * made under the same terms and conditions under which the user * received it from the SOFA Center. * * 8. The user shall not cause the Software to be brought into * disrepute, either by misuse, or use for inappropriate tasks, or by * inappropriate modification. * * 9. The Software is provided to the user "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 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. * * 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