FACT++  1.0
fw2xy.c
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1 #include "erfa.h"
2 
3 void eraFw2xy(double gamb, double phib, double psi, double eps,
4  double *x, double *y)
5 /*
6 ** - - - - - - - - -
7 ** e r a F w 2 x y
8 ** - - - - - - - - -
9 **
10 ** CIP X,Y given Fukushima-Williams bias-precession-nutation angles.
11 **
12 ** Given:
13 ** gamb double F-W angle gamma_bar (radians)
14 ** phib double F-W angle phi_bar (radians)
15 ** psi double F-W angle psi (radians)
16 ** eps double F-W angle epsilon (radians)
17 **
18 ** Returned:
19 ** x,y double CIP unit vector X,Y
20 **
21 ** Notes:
22 **
23 ** 1) Naming the following points:
24 **
25 ** e = J2000.0 ecliptic pole,
26 ** p = GCRS pole
27 ** E = ecliptic pole of date,
28 ** and P = CIP,
29 **
30 ** the four Fukushima-Williams angles are as follows:
31 **
32 ** gamb = gamma = epE
33 ** phib = phi = pE
34 ** psi = psi = pEP
35 ** eps = epsilon = EP
36 **
37 ** 2) The matrix representing the combined effects of frame bias,
38 ** precession and nutation is:
39 **
40 ** NxPxB = R_1(-epsA).R_3(-psi).R_1(phib).R_3(gamb)
41 **
42 ** The returned values x,y are elements [2][0] and [2][1] of the
43 ** matrix. Near J2000.0, they are essentially angles in radians.
44 **
45 ** Called:
46 ** eraFw2m F-W angles to r-matrix
47 ** eraBpn2xy extract CIP X,Y coordinates from NPB matrix
48 **
49 ** Reference:
50 **
51 ** Hilton, J. et al., 2006, Celest.Mech.Dyn.Astron. 94, 351
52 **
53 ** Copyright (C) 2013-2015, NumFOCUS Foundation.
54 ** Derived, with permission, from the SOFA library. See notes at end of file.
55 */
56 {
57  double r[3][3];
58 
59 /* Form NxPxB matrix. */
60  eraFw2m(gamb, phib, psi, eps, r);
61 
62 /* Extract CIP X,Y. */
63  eraBpn2xy(r, x, y);
64 
65  return;
66 
67 }
68 /*----------------------------------------------------------------------
69 **
70 **
71 ** Copyright (C) 2013-2015, NumFOCUS Foundation.
72 ** All rights reserved.
73 **
74 ** This library is derived, with permission, from the International
75 ** Astronomical Union's "Standards of Fundamental Astronomy" library,
76 ** available from http://www.iausofa.org.
77 **
78 ** The ERFA version is intended to retain identical functionality to
79 ** the SOFA library, but made distinct through different function and
80 ** file names, as set out in the SOFA license conditions. The SOFA
81 ** original has a role as a reference standard for the IAU and IERS,
82 ** and consequently redistribution is permitted only in its unaltered
83 ** state. The ERFA version is not subject to this restriction and
84 ** therefore can be included in distributions which do not support the
85 ** concept of "read only" software.
86 **
87 ** Although the intent is to replicate the SOFA API (other than
88 ** replacement of prefix names) and results (with the exception of
89 ** bugs; any that are discovered will be fixed), SOFA is not
90 ** responsible for any errors found in this version of the library.
91 **
92 ** If you wish to acknowledge the SOFA heritage, please acknowledge
93 ** that you are using a library derived from SOFA, rather than SOFA
94 ** itself.
95 **
96 **
97 ** TERMS AND CONDITIONS
98 **
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100 ** modification, are permitted provided that the following conditions
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102 **
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104 ** notice, this list of conditions and the following disclaimer.
105 **
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111 ** 3 Neither the name of the Standards Of Fundamental Astronomy Board,
112 ** the International Astronomical Union nor the names of its
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116 ** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
117 ** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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119 ** FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
120 ** COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
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129 */
eraFw2m
void eraFw2m(double gamb, double phib, double psi, double eps, double r[3][3])
Definition: fw2m.c:3
eraFw2xy
void eraFw2xy(double gamb, double phib, double psi, double eps, double *x, double *y)
Definition: fw2xy.c:3
eraBpn2xy
void eraBpn2xy(double rbpn[3][3], double *x, double *y)
Definition: bpn2xy.c:3