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Diffstat (limited to 'ast/erfa/prec76.c')
| -rw-r--r-- | ast/erfa/prec76.c | 157 |
1 files changed, 157 insertions, 0 deletions
diff --git a/ast/erfa/prec76.c b/ast/erfa/prec76.c new file mode 100644 index 0000000..4c47985 --- /dev/null +++ b/ast/erfa/prec76.c @@ -0,0 +1,157 @@ +#include "erfa.h" + +void eraPrec76(double date01, double date02, double date11, double date12, + double *zeta, double *z, double *theta) +/* +** - - - - - - - - - - +** e r a P r e c 7 6 +** - - - - - - - - - - +** +** IAU 1976 precession model. +** +** This function forms the three Euler angles which implement general +** precession between two dates, using the IAU 1976 model (as for the +** FK5 catalog). +** +** Given: +** date01,date02 double TDB starting date (Note 1) +** date11,date12 double TDB ending date (Note 1) +** +** Returned: +** zeta double 1st rotation: radians cw around z +** z double 3rd rotation: radians cw around z +** theta double 2nd rotation: radians ccw around y +** +** Notes: +** +** 1) The dates date01+date02 and date11+date12 are Julian Dates, +** apportioned in any convenient way between the arguments daten1 +** and daten2. For example, JD(TDB)=2450123.7 could be expressed in +** any of these ways, among others: +** +** daten1 daten2 +** +** 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 +** optimum resolution. The MJD method and the date & time methods +** are both good compromises between resolution and convenience. +** The two dates may be expressed using different methods, but at +** the risk of losing some resolution. +** +** 2) The accumulated precession angles zeta, z, theta are expressed +** through canonical polynomials which are valid only for a limited +** time span. In addition, the IAU 1976 precession rate is known to +** be imperfect. The absolute accuracy of the present formulation +** is better than 0.1 arcsec from 1960AD to 2040AD, better than +** 1 arcsec from 1640AD to 2360AD, and remains below 3 arcsec for +** the whole of the period 500BC to 3000AD. The errors exceed +** 10 arcsec outside the range 1200BC to 3900AD, exceed 100 arcsec +** outside 4200BC to 5600AD and exceed 1000 arcsec outside 6800BC to +** 8200AD. +** +** 3) The three angles are returned in the conventional order, which +** is not the same as the order of the corresponding Euler +** rotations. The precession matrix is +** R_3(-z) x R_2(+theta) x R_3(-zeta). +** +** Reference: +** +** Lieske, J.H., 1979, Astron.Astrophys. 73, 282, equations +** (6) & (7), p283. +** +** Copyright (C) 2013-2016, NumFOCUS Foundation. +** Derived, with permission, from the SOFA library. See notes at end of file. +*/ +{ + double t0, t, tas2r, w; + + +/* Interval between fundamental epoch J2000.0 and start date (JC). */ + t0 = ((date01 - ERFA_DJ00) + date02) / ERFA_DJC; + +/* Interval over which precession required (JC). */ + t = ((date11 - date01) + (date12 - date02)) / ERFA_DJC; + +/* Euler angles. */ + tas2r = t * ERFA_DAS2R; + w = 2306.2181 + (1.39656 - 0.000139 * t0) * t0; + + *zeta = (w + ((0.30188 - 0.000344 * t0) + 0.017998 * t) * t) * tas2r; + + *z = (w + ((1.09468 + 0.000066 * t0) + 0.018203 * t) * t) * tas2r; + + *theta = ((2004.3109 + (-0.85330 - 0.000217 * t0) * t0) + + ((-0.42665 - 0.000217 * t0) - 0.041833 * t) * t) * tas2r; + + 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. +** +*/ |