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Diffstat (limited to 'ast/erfa/pb06.c')
| -rw-r--r-- | ast/erfa/pb06.c | 153 |
1 files changed, 153 insertions, 0 deletions
diff --git a/ast/erfa/pb06.c b/ast/erfa/pb06.c new file mode 100644 index 0000000..dc8d60d --- /dev/null +++ b/ast/erfa/pb06.c @@ -0,0 +1,153 @@ +#include "erfa.h" + +void eraPb06(double date1, double date2, + double *bzeta, double *bz, double *btheta) +/* +** - - - - - - - - +** e r a P b 0 6 +** - - - - - - - - +** +** This function forms three Euler angles which implement general +** precession from epoch J2000.0, using the IAU 2006 model. Frame +** bias (the offset between ICRS and mean J2000.0) is included. +** +** Given: +** date1,date2 double TT as a 2-part Julian Date (Note 1) +** +** Returned: +** bzeta double 1st rotation: radians cw around z +** bz double 3rd rotation: radians cw around z +** btheta double 2nd rotation: radians ccw around y +** +** 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 traditional accumulated precession angles zeta_A, z_A, +** theta_A cannot be obtained in the usual way, namely through +** polynomial expressions, because of the frame bias. The latter +** means that two of the angles undergo rapid changes near this +** date. They are instead the results of decomposing the +** precession-bias matrix obtained by using the Fukushima-Williams +** method, which does not suffer from the problem. The +** decomposition returns values which can be used in the +** conventional formulation and which include frame bias. +** +** 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-bias matrix is +** R_3(-z) x R_2(+theta) x R_3(-zeta). +** +** 4) Should zeta_A, z_A, theta_A angles be required that do not +** contain frame bias, they are available by calling the ERFA +** function eraP06e. +** +** Called: +** eraPmat06 PB matrix, IAU 2006 +** eraRz rotate around Z-axis +** +** Copyright (C) 2013-2014, NumFOCUS Foundation. +** Derived, with permission, from the SOFA library. See notes at end of file. +*/ +{ + double r[3][3], r31, r32; + + +/* Precession matrix via Fukushima-Williams angles. */ + eraPmat06(date1, date2, r); + +/* Solve for z. */ + *bz = atan2(r[1][2], r[0][2]); + +/* Remove it from the matrix. */ + eraRz(*bz, r); + +/* Solve for the remaining two angles. */ + *bzeta = atan2 (r[1][0], r[1][1]); + r31 = r[2][0]; + r32 = r[2][1]; + *btheta = atan2(-ERFA_DSIGN(sqrt(r31 * r31 + r32 * r32), r[0][2]), + r[2][2]); + + 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. +** +*/ |