FACT++  1.0
s00b.c
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1 #include "erfa.h"
2 
3 double eraS00b(double date1, double date2)
4 /*
5 ** - - - - - - - -
6 ** e r a S 0 0 b
7 ** - - - - - - - -
8 **
9 ** The CIO locator s, positioning the Celestial Intermediate Origin on
10 ** the equator of the Celestial Intermediate Pole, using the IAU 2000B
11 ** precession-nutation model.
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
48 ** is more compact than a direct series for s would be. The present
49 ** function uses the IAU 2000B truncated nutation model when
50 ** predicting the CIP position. The function eraS00a uses instead
51 ** the full IAU 2000A model, but with no significant increase in
52 ** accuracy and at some cost in speed.
53 **
54 ** Called:
55 ** eraPnm00b classical NPB matrix, IAU 2000B
56 ** eraBnp2xy extract CIP X,Y from the BPN matrix
57 ** eraS00 the CIO locator s, given X,Y, IAU 2000A
58 **
59 ** References:
60 **
61 ** Capitaine, N., Chapront, J., Lambert, S. and Wallace, P.,
62 ** "Expressions for the Celestial Intermediate Pole and Celestial
63 ** Ephemeris Origin consistent with the IAU 2000A precession-
64 ** nutation model", Astron.Astrophys. 400, 1145-1154 (2003)
65 **
66 ** n.b. The celestial ephemeris origin (CEO) was renamed "celestial
67 ** intermediate origin" (CIO) by IAU 2006 Resolution 2.
68 **
69 ** McCarthy, D. D., Petit, G. (eds.), IERS Conventions (2003),
70 ** IERS Technical Note No. 32, BKG (2004)
71 **
72 ** Copyright (C) 2013-2015, NumFOCUS Foundation.
73 ** Derived, with permission, from the SOFA library. See notes at end of file.
74 */
75 {
76  double rbpn[3][3], x, y, s;
77 
78 /* Bias-precession-nutation-matrix, IAU 2000B. */
79  eraPnm00b(date1, date2, rbpn);
80 
81 /* Extract the CIP coordinates. */
82  eraBpn2xy(rbpn, &x, &y);
83 
84 /* Compute the CIO locator s, given the CIP coordinates. */
85  s = eraS00(date1, date2, x, y);
86 
87  return s;
88 
89 }
90 /*----------------------------------------------------------------------
91 **
92 **
93 ** Copyright (C) 2013-2015, NumFOCUS Foundation.
94 ** All rights reserved.
95 **
96 ** This library is derived, with permission, from the International
97 ** Astronomical Union's "Standards of Fundamental Astronomy" library,
98 ** available from http://www.iausofa.org.
99 **
100 ** The ERFA version is intended to retain identical functionality to
101 ** the SOFA library, but made distinct through different function and
102 ** file names, as set out in the SOFA license conditions. The SOFA
103 ** original has a role as a reference standard for the IAU and IERS,
104 ** and consequently redistribution is permitted only in its unaltered
105 ** state. The ERFA version is not subject to this restriction and
106 ** therefore can be included in distributions which do not support the
107 ** concept of "read only" software.
108 **
109 ** Although the intent is to replicate the SOFA API (other than
110 ** replacement of prefix names) and results (with the exception of
111 ** bugs; any that are discovered will be fixed), SOFA is not
112 ** responsible for any errors found in this version of the library.
113 **
114 ** If you wish to acknowledge the SOFA heritage, please acknowledge
115 ** that you are using a library derived from SOFA, rather than SOFA
116 ** itself.
117 **
118 **
119 ** TERMS AND CONDITIONS
120 **
121 ** Redistribution and use in source and binary forms, with or without
122 ** modification, are permitted provided that the following conditions
123 ** are met:
124 **
125 ** 1 Redistributions of source code must retain the above copyright
126 ** notice, this list of conditions and the following disclaimer.
127 **
128 ** 2 Redistributions in binary form must reproduce the above copyright
129 ** notice, this list of conditions and the following disclaimer in
130 ** the documentation and/or other materials provided with the
131 ** distribution.
132 **
133 ** 3 Neither the name of the Standards Of Fundamental Astronomy Board,
134 ** the International Astronomical Union nor the names of its
135 ** contributors may be used to endorse or promote products derived
136 ** from this software without specific prior written permission.
137 **
138 ** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
139 ** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
140 ** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
141 ** FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
142 ** COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
143 ** INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
144 ** BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
145 ** LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
146 ** CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
147 ** LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
148 ** ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
149 ** POSSIBILITY OF SUCH DAMAGE.
150 **
151 */
eraS00
double eraS00(double date1, double date2, double x, double y)
Definition: s00.c:3
eraPnm00b
void eraPnm00b(double date1, double date2, double rbpn[3][3])
Definition: pnm00b.c:3
eraBpn2xy
void eraBpn2xy(double rbpn[3][3], double *x, double *y)
Definition: bpn2xy.c:3
eraS00b
double eraS00b(double date1, double date2)
Definition: s00b.c:3