/rust/registry/src/index.crates.io-1949cf8c6b5b557f/sofars-0.6.1/src/pnp/c2i06a.rs

Source
use crate::pnp::{bpn2xy, c2ixys, pnm06a, s06};

///  Form the celestial-to-intermediate matrix for a given date using the
///  IAU 2006 precession and IAU 2000A nutation models.
///
///  Given:
///     date1,date2 double       TT as a 2-part Julian Date (Note 1)
///
///  Returned (function value):
///                 double[3][3] celestial-to-intermediate matrix (Note 2)
///
///  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 matrix rc2i is the first stage in the transformation 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.
///
///  Called:
///     iauPnm06a    classical NPB matrix, IAU 2006/2000A
///     iauBpn2xy    extract CIP X,Y coordinates from NPB matrix
///     iauS06       the CIO locator s, given X,Y, IAU 2006
///     iauC2ixys    celestial-to-intermediate matrix, given X,Y and s
///
///  References:
///
///     McCarthy, D. D., Petit, G. (eds.), 2004, IERS Conventions (2003),
///     IERS Technical Note No. 32, BKG
pub fn c2i06a(date1: f64, date2: f64) -> [[f64; 3]; 3] {
    /* Obtain the celestial-to-true matrix (IAU 2006/2000A). */
    let rbpn = pnm06a(date1, date2);

    /* Extract the X,Y coordinates. */
    let (x, y) = bpn2xy(&rbpn);

    /* Obtain the CIO locator. */
    let s = s06(date1, date2, x, y);

    /* Form the celestial-to-intermediate matrix. */
    c2ixys(x, y, s)
}

Coverage Report

Created: 2026-07-30 06:46

Line	Count	Source
1		use crate::pnp::{bpn2xy, c2ixys, pnm06a, s06};
2
3		/// Form the celestial-to-intermediate matrix for a given date using the
4		/// IAU 2006 precession and IAU 2000A nutation models.
5		///
6		/// Given:
7		/// date1,date2 double TT as a 2-part Julian Date (Note 1)
8		///
9		/// Returned (function value):
10		/// double[3][3] celestial-to-intermediate matrix (Note 2)
11		///
12		/// Notes:
13		///
14		/// 1) The TT date date1+date2 is a Julian Date, apportioned in any
15		/// convenient way between the two arguments. For example,
16		/// JD(TT)=2450123.7 could be expressed in any of these ways,
17		/// among others:
18		///
19		/// date1 date2
20		///
21		/// 2450123.7 0.0 (JD method)
22		/// 2451545.0 -1421.3 (J2000 method)
23		/// 2400000.5 50123.2 (MJD method)
24		/// 2450123.5 0.2 (date & time method)
25		///
26		/// The JD method is the most natural and convenient to use in
27		/// cases where the loss of several decimal digits of resolution
28		/// is acceptable. The J2000 method is best matched to the way
29		/// the argument is handled internally and will deliver the
30		/// optimum resolution. The MJD method and the date & time methods
31		/// are both good compromises between resolution and convenience.
32		///
33		/// 2) The matrix rc2i is the first stage in the transformation from
34		/// celestial to terrestrial coordinates:
35		///
36		/// [TRS] = RPOM * R_3(ERA) * rc2i * [CRS]
37		///
38		/// = RC2T * [CRS]
39		///
40		/// where [CRS] is a vector in the Geocentric Celestial Reference
41		/// System and [TRS] is a vector in the International Terrestrial
42		/// Reference System (see IERS Conventions 2003), ERA is the Earth
43		/// Rotation Angle and RPOM is the polar motion matrix.
44		///
45		/// Called:
46		/// iauPnm06a classical NPB matrix, IAU 2006/2000A
47		/// iauBpn2xy extract CIP X,Y coordinates from NPB matrix
48		/// iauS06 the CIO locator s, given X,Y, IAU 2006
49		/// iauC2ixys celestial-to-intermediate matrix, given X,Y and s
50		///
51		/// References:
52		///
53		/// McCarthy, D. D., Petit, G. (eds.), 2004, IERS Conventions (2003),
54		/// IERS Technical Note No. 32, BKG
55	0	pub fn c2i06a(date1: f64, date2: f64) -> [[f64; 3]; 3] {
56		/* Obtain the celestial-to-true matrix (IAU 2006/2000A). */
57	0	let rbpn = pnm06a(date1, date2);
58
59		/* Extract the X,Y coordinates. */
60	0	let (x, y) = bpn2xy(&rbpn);
61
62		/* Obtain the CIO locator. */
63	0	let s = s06(date1, date2, x, y);
64
65		/* Form the celestial-to-intermediate matrix. */
66	0	c2ixys(x, y, s)
67	0	}