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Diffstat (limited to 'ast/erfa/c2ixys.c')
| -rw-r--r-- | ast/erfa/c2ixys.c | 132 |
1 files changed, 132 insertions, 0 deletions
diff --git a/ast/erfa/c2ixys.c b/ast/erfa/c2ixys.c new file mode 100644 index 0000000..1c92687 --- /dev/null +++ b/ast/erfa/c2ixys.c @@ -0,0 +1,132 @@ +#include "erfa.h" + +void eraC2ixys(double x, double y, double s, double rc2i[3][3]) +/* +** - - - - - - - - - - +** e r a 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. +** +** Given: +** x,y double Celestial Intermediate Pole (Note 1) +** s double the CIO locator s (Note 2) +** +** Returned: +** rc2i double[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: +** eraIr initialize r-matrix to identity +** eraRz rotate around Z-axis +** eraRy rotate around Y-axis +** +** Reference: +** +** McCarthy, D. D., Petit, G. (eds.), IERS Conventions (2003), +** IERS Technical Note No. 32, BKG (2004) +** +** Copyright (C) 2013-2016, NumFOCUS Foundation. +** Derived, with permission, from the SOFA library. See notes at end of file. +*/ +{ + double r2, e, d; + + +/* Obtain the spherical angles E and d. */ + r2 = x*x + y*y; + e = (r2 > 0.0) ? atan2(y, x) : 0.0; + d = atan(sqrt(r2 / (1.0 - r2))); + +/* Form the matrix. */ + eraIr(rc2i); + eraRz(e, rc2i); + eraRy(d, rc2i); + eraRz(-(e+s), rc2i); + + return; + +} +/*---------------------------------------------------------------------- +** +** +** Copyright (C) 2013-2016, NumFOCUS Foundation. +** All rights reserved. +** +** This library is derived, with permission, from the International +** Astronomical Union's "Standards of Fundamental Astronomy" library, +** available from http://www.iausofa.org. +** +** The ERFA version is intended to retain identical functionality to +** the SOFA library, but made distinct through different function and +** file names, as set out in the SOFA license conditions. The SOFA +** original has a role as a reference standard for the IAU and IERS, +** and consequently redistribution is permitted only in its unaltered +** state. The ERFA version is not subject to this restriction and +** therefore can be included in distributions which do not support the +** concept of "read only" software. +** +** Although the intent is to replicate the SOFA API (other than +** replacement of prefix names) and results (with the exception of +** bugs; any that are discovered will be fixed), SOFA is not +** responsible for any errors found in this version of the library. +** +** If you wish to acknowledge the SOFA heritage, please acknowledge +** that you are using a library derived from SOFA, rather than SOFA +** itself. +** +** +** TERMS AND CONDITIONS +** +** Redistribution and use in source and binary forms, with or without +** modification, are permitted provided that the following conditions +** are met: +** +** 1 Redistributions of source code must retain the above copyright +** notice, this list of conditions and the following disclaimer. +** +** 2 Redistributions in binary form must reproduce the above copyright +** notice, this list of conditions and the following disclaimer in +** the documentation and/or other materials provided with the +** distribution. +** +** 3 Neither the name of the Standards Of Fundamental Astronomy Board, +** the International Astronomical Union nor the names of its +** contributors may be used to endorse or promote products derived +** from this software without specific prior written permission. +** +** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS +** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT +** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS +** FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE +** COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, +** INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, +** BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; +** LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER +** CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT +** LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN +** ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE +** POSSIBILITY OF SUCH DAMAGE. +** +*/ |