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Diffstat (limited to 'ast/erfa/xys00a.c')
| -rw-r--r-- | ast/erfa/xys00a.c | 142 |
1 files changed, 142 insertions, 0 deletions
diff --git a/ast/erfa/xys00a.c b/ast/erfa/xys00a.c new file mode 100644 index 0000000..411627e --- /dev/null +++ b/ast/erfa/xys00a.c @@ -0,0 +1,142 @@ +#include "erfa.h" + +void eraXys00a(double date1, double date2, + double *x, double *y, double *s) +/* +** - - - - - - - - - - +** e r a X y s 0 0 a +** - - - - - - - - - - +** +** For a given TT date, compute the X,Y coordinates of the Celestial +** Intermediate Pole and the CIO locator s, using the IAU 2000A +** precession-nutation model. +** +** Given: +** date1,date2 double TT as a 2-part Julian Date (Note 1) +** +** Returned: +** x,y double Celestial Intermediate Pole (Note 2) +** s double the CIO locator s (Note 2) +** +** Notes: +** +** 1) The TT date date1+date2 is a Julian Date, apportioned in any +** convenient way between the two arguments. For example, +** JD(TT)=2450123.7 could be expressed in any of these ways, +** among others: +** +** date1 date2 +** +** 2450123.7 0.0 (JD method) +** 2451545.0 -1421.3 (J2000 method) +** 2400000.5 50123.2 (MJD method) +** 2450123.5 0.2 (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 method is best matched to the way +** the argument is handled internally and will deliver the +** optimum resolution. The MJD method and the date & time methods +** are both good compromises between resolution and convenience. +** +** 2) The Celestial Intermediate Pole coordinates are the x,y +** components of the unit vector in the Geocentric Celestial +** Reference System. +** +** 3) The CIO locator s (in radians) positions the Celestial +** Intermediate Origin on the equator of the CIP. +** +** 4) A faster, but slightly less accurate result (about 1 mas for +** X,Y), can be obtained by using instead the eraXys00b function. +** +** Called: +** eraPnm00a classical NPB matrix, IAU 2000A +** eraBpn2xy extract CIP X,Y coordinates from NPB matrix +** eraS00 the CIO locator s, given X,Y, IAU 2000A +** +** Reference: +** +** McCarthy, D. D., Petit, G. (eds.), IERS Conventions (2003), +** IERS Technical Note No. 32, BKG (2004) +** +** Copyright (C) 2013-2014, NumFOCUS Foundation. +** Derived, with permission, from the SOFA library. See notes at end of file. +*/ +{ + double rbpn[3][3]; + + +/* Form the bias-precession-nutation matrix, IAU 2000A. */ + eraPnm00a(date1, date2, rbpn); + +/* Extract X,Y. */ + eraBpn2xy(rbpn, x, y); + +/* Obtain s. */ + *s = eraS00(date1, date2, *x, *y); + + return; + +} +/*---------------------------------------------------------------------- +** +** +** Copyright (C) 2013-2014, 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. +** +*/ |