FACT++  1.0
s06a.c
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1 #include "erfa.h"
2 
3 double eraS06a(double date1, double date2)
4 /*
5 ** - - - - - - - -
6 ** e r a S 0 6 a
7 ** - - - - - - - -
8 **
9 ** The CIO locator s, positioning the Celestial Intermediate Origin on
10 ** the equator of the Celestial Intermediate Pole, using the IAU 2006
11 ** precession and IAU 2000A nutation models.
12 **
13 ** Given:
14 ** date1,date2 double TT as a 2-part Julian Date (Note 1)
15 **
16 ** Returned (function value):
17 ** double the CIO locator s in radians (Note 2)
18 **
19 ** Notes:
20 **
21 ** 1) The TT date date1+date2 is a Julian Date, apportioned in any
22 ** convenient way between the two arguments. For example,
23 ** JD(TT)=2450123.7 could be expressed in any of these ways,
24 ** among others:
25 **
26 ** date1 date2
27 **
28 ** 2450123.7 0.0 (JD method)
29 ** 2451545.0 -1421.3 (J2000 method)
30 ** 2400000.5 50123.2 (MJD method)
31 ** 2450123.5 0.2 (date & time method)
32 **
33 ** The JD method is the most natural and convenient to use in
34 ** cases where the loss of several decimal digits of resolution
35 ** is acceptable. The J2000 method is best matched to the way
36 ** the argument is handled internally and will deliver the
37 ** optimum resolution. The MJD method and the date & time methods
38 ** are both good compromises between resolution and convenience.
39 **
40 ** 2) The CIO locator s is the difference between the right ascensions
41 ** of the same point in two systems. The two systems are the GCRS
42 ** and the CIP,CIO, and the point is the ascending node of the
43 ** CIP equator. The CIO locator s remains a small fraction of
44 ** 1 arcsecond throughout 1900-2100.
45 **
46 ** 3) The series used to compute s is in fact for s+XY/2, where X and Y
47 ** are the x and y components of the CIP unit vector; this series is
48 ** more compact than a direct series for s would be. The present
49 ** function uses the full IAU 2000A nutation model when predicting
50 ** the CIP position.
51 **
52 ** Called:
53 ** eraPnm06a classical NPB matrix, IAU 2006/2000A
54 ** eraBpn2xy extract CIP X,Y coordinates from NPB matrix
55 ** eraS06 the CIO locator s, given X,Y, IAU 2006
56 **
57 ** References:
58 **
59 ** Capitaine, N., Chapront, J., Lambert, S. and Wallace, P.,
60 ** "Expressions for the Celestial Intermediate Pole and Celestial
61 ** Ephemeris Origin consistent with the IAU 2000A precession-
62 ** nutation model", Astron.Astrophys. 400, 1145-1154 (2003)
63 **
64 ** n.b. The celestial ephemeris origin (CEO) was renamed "celestial
65 ** intermediate origin" (CIO) by IAU 2006 Resolution 2.
66 **
67 ** Capitaine, N. & Wallace, P.T., 2006, Astron.Astrophys. 450, 855
68 **
69 ** McCarthy, D. D., Petit, G. (eds.), 2004, IERS Conventions (2003),
70 ** IERS Technical Note No. 32, BKG
71 **
72 ** Wallace, P.T. & Capitaine, N., 2006, Astron.Astrophys. 459, 981
73 **
74 ** Copyright (C) 2013-2015, NumFOCUS Foundation.
75 ** Derived, with permission, from the SOFA library. See notes at end of file.
76 */
77 {
78  double rnpb[3][3], x, y, s;
79 
80 /* Bias-precession-nutation-matrix, IAU 20006/2000A. */
81  eraPnm06a(date1, date2, rnpb);
82 
83 /* Extract the CIP coordinates. */
84  eraBpn2xy(rnpb, &x, &y);
85 
86 /* Compute the CIO locator s, given the CIP coordinates. */
87  s = eraS06(date1, date2, x, y);
88 
89  return s;
90 
91 }
92 /*----------------------------------------------------------------------
93 **
94 **
95 ** Copyright (C) 2013-2015, NumFOCUS Foundation.
96 ** All rights reserved.
97 **
98 ** This library is derived, with permission, from the International
99 ** Astronomical Union's "Standards of Fundamental Astronomy" library,
100 ** available from http://www.iausofa.org.
101 **
102 ** The ERFA version is intended to retain identical functionality to
103 ** the SOFA library, but made distinct through different function and
104 ** file names, as set out in the SOFA license conditions. The SOFA
105 ** original has a role as a reference standard for the IAU and IERS,
106 ** and consequently redistribution is permitted only in its unaltered
107 ** state. The ERFA version is not subject to this restriction and
108 ** therefore can be included in distributions which do not support the
109 ** concept of "read only" software.
110 **
111 ** Although the intent is to replicate the SOFA API (other than
112 ** replacement of prefix names) and results (with the exception of
113 ** bugs; any that are discovered will be fixed), SOFA is not
114 ** responsible for any errors found in this version of the library.
115 **
116 ** If you wish to acknowledge the SOFA heritage, please acknowledge
117 ** that you are using a library derived from SOFA, rather than SOFA
118 ** itself.
119 **
120 **
121 ** TERMS AND CONDITIONS
122 **
123 ** Redistribution and use in source and binary forms, with or without
124 ** modification, are permitted provided that the following conditions
125 ** are met:
126 **
127 ** 1 Redistributions of source code must retain the above copyright
128 ** notice, this list of conditions and the following disclaimer.
129 **
130 ** 2 Redistributions in binary form must reproduce the above copyright
131 ** notice, this list of conditions and the following disclaimer in
132 ** the documentation and/or other materials provided with the
133 ** distribution.
134 **
135 ** 3 Neither the name of the Standards Of Fundamental Astronomy Board,
136 ** the International Astronomical Union nor the names of its
137 ** contributors may be used to endorse or promote products derived
138 ** from this software without specific prior written permission.
139 **
140 ** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
141 ** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
142 ** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
143 ** FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
144 ** COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
145 ** INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
146 ** BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
147 ** LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
148 ** CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
149 ** LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
150 ** ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
151 ** POSSIBILITY OF SUCH DAMAGE.
152 **
153 */
eraPnm06a
void eraPnm06a(double date1, double date2, double rnpb[3][3])
Definition: pnm06a.c:3
eraS06a
double eraS06a(double date1, double date2)
Definition: s06a.c:3
eraBpn2xy
void eraBpn2xy(double rbpn[3][3], double *x, double *y)
Definition: bpn2xy.c:3
eraS06
double eraS06(double date1, double date2, double x, double y)
Definition: s06.c:3