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Diffstat (limited to 'ast/erfa/c2txy.c')
| -rw-r--r-- | ast/erfa/c2txy.c | 168 |
1 files changed, 168 insertions, 0 deletions
diff --git a/ast/erfa/c2txy.c b/ast/erfa/c2txy.c new file mode 100644 index 0000000..198c7a8 --- /dev/null +++ b/ast/erfa/c2txy.c @@ -0,0 +1,168 @@ +#include "erfa.h" + +void eraC2txy(double tta, double ttb, double uta, double utb, + double x, double y, double xp, double yp, + double rc2t[3][3]) +/* +** - - - - - - - - - +** e r a C 2 t x y +** - - - - - - - - - +** +** Form the celestial to terrestrial matrix given the date, the UT1, +** the CIP coordinates and the polar motion. IAU 2000. +** +** Given: +** tta,ttb double TT as a 2-part Julian Date (Note 1) +** uta,utb double UT1 as a 2-part Julian Date (Note 1) +** x,y double Celestial Intermediate Pole (Note 2) +** xp,yp double coordinates of the pole (radians, Note 3) +** +** Returned: +** rc2t double[3][3] celestial-to-terrestrial matrix (Note 4) +** +** Notes: +** +** 1) The TT and UT1 dates tta+ttb and uta+utb are Julian Dates, +** apportioned in any convenient way between the arguments uta and +** utb. For example, JD(UT1)=2450123.7 could be expressed in any o +** these ways, among others: +** +** uta utb +** +** 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 and MJD methods are good compromises +** between resolution and convenience. In the case of uta,utb, the +** date & time method is best matched to the Earth rotation angle +** algorithm used: maximum precision is delivered when the uta +** argument is for 0hrs UT1 on the day in question and the utb +** argument lies in the range 0 to 1, or vice versa. +** +** 2) The Celestial Intermediate Pole coordinates are the x,y +** components of the unit vector in the Geocentric Celestial +** Reference System. +** +** 3) The arguments xp and yp are the coordinates (in radians) of the +** Celestial Intermediate Pole with respect to the International +** Terrestrial Reference System (see IERS Conventions 2003), +** measured along the meridians to 0 and 90 deg west respectively. +** +** 4) The matrix rc2t transforms 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. +** +** 5) Although its name does not include "00", This function is in fact +** specific to the IAU 2000 models. +** +** Called: +** eraC2ixy celestial-to-intermediate matrix, given X,Y +** eraEra00 Earth rotation angle, IAU 2000 +** eraSp00 the TIO locator s', IERS 2000 +** eraPom00 polar motion matrix +** eraC2tcio form CIO-based celestial-to-terrestrial matrix +** +** 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 rc2i[3][3], era, sp, rpom[3][3]; + + +/* Form the celestial-to-intermediate matrix for this TT. */ + eraC2ixy(tta, ttb, x, y, rc2i); + +/* Predict the Earth rotation angle for this UT1. */ + era = eraEra00(uta, utb); + +/* Estimate s'. */ + sp = eraSp00(tta, ttb); + +/* Form the polar motion matrix. */ + eraPom00(xp, yp, sp, rpom); + +/* Combine to form the celestial-to-terrestrial matrix. */ + eraC2tcio(rc2i, era, rpom, rc2t); + + 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. +** +*/ |