rfa 0.5.9

A port ERFA to Rust.
Documentation 
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use crate::{rfam::{URSA_D2PI, URSA_DAYSEC}, utils::*};
use crate::prec_nut::pom00::pom00;
use crate::vector_matrix::matrix_vec_prod::trxp;
use crate::geodetic_geocentric::gd2gc::gd2gc;
/*
**  - - - - - - - - -
**   e r a P v t o b
**  - - - - - - - - -
**
**  Position and velocity of a terrestrial observing station.
**
**  Given:
**     elong   double       longitude (radians, east +ve, Note 1)
**     phi     double       latitude (geodetic, radians, Note 1)
**     hm      double       height above ref. ellipsoid (geodetic, m)
**     xp,yp   double       coordinates of the pole (radians, Note 2)
**     sp      double       the TIO locator s' (radians, Note 2)
**     theta   double       Earth rotation angle (radians, Note 3)
**
**  Returned:
**     pv      double[2][3] position/velocity vector (m, m/s, CIRS)
**
**  Notes:
**
**  1) The terrestrial coordinates are with respect to the ERFA_WGS84
**     reference ellipsoid.
**
**  2) xp and yp are the coordinates (in radians) of the Celestial
**     Intermediate Pole with respect to the International Terrestrial
**     Reference System (see IERS Conventions), measured along the
**     meridians 0 and 90 deg west respectively.  sp is the TIO locator
**     s', in radians, which positions the Terrestrial Intermediate
**     Origin on the equator.  For many applications, xp, yp and
**     (especially) sp can be set to zero.
**
**  3) If theta is Greenwich apparent sidereal time instead of Earth
**     rotation angle, the result is with respect to the true equator
**     and equinox of date, i.e. with the x-axis at the equinox rather
**     than the celestial intermediate origin.
**
**  4) The velocity units are meters per UT1 second, not per SI second.
**     This is unlikely to have any practical consequences in the modern
**     era.
**
**  5) No validation is performed on the arguments.  Error cases that
**     could lead to arithmetic exceptions are trapped by the eraGd2gc
**     function, and the result set to zeros.
**
**  References:
**
**     McCarthy, D. D., Petit, G. (eds.), IERS Conventions (2003),
**     IERS Technical Note No. 32, BKG (2004)
**
**     Urban, S. & Seidelmann, P. K. (eds), Explanatory Supplement to
**     the Astronomical Almanac, 3rd ed., University Science Books
**     (2013), Section 7.4.3.3.
**
**  Called:
**     eraGd2gc     geodetic to geocentric transformation
**     eraPom00     polar motion matrix
**     eraTrxp      product of transpose of r-matrix and p-vector
**
**  This revision:   2021 February 24
**
**  Copyright (C) 2013-2021, NumFOCUS Foundation.
**  Derived, with permission, from the SOFA library.  See notes at end of file.
*/
pub fn pvtob(elong: f64, phi: f64, height: f64, xp: f64,
    yp: f64, sp: f64, theta: f64, pv: &mut [[f64; 3]; 2])

{
/* Earth rotation rate in radians per UT1 second */
   const OM: f64 = 1.00273781191135448 * URSA_D2PI / URSA_DAYSEC;
    let mut xyzm = [0.0; 3];
    let mut xyz = [0.0; 3];
    let mut rpm = [[0.0; 3]; 3];


/* Geodetic to geocentric transformation (ERFA_WGS84). */
   gd2gc(1, elong, phi, height, &mut xyzm);

/* Polar motion and TIO position. */
   pom00(xp, yp, sp, &mut rpm);
   trxp(&rpm, &xyzm, &mut xyz);
   let x = xyz[0];
   let y = xyz[1];
   let z = xyz[2];

/* Functions of ERA. */
   let s = sin(theta);
   let c = cos(theta);

/* Position. */
   pv[0][0] = c*x - s*y;
   pv[0][1] = s*x + c*y;
   pv[0][2] = z;

/* Velocity. */
   pv[1][0] = OM * ( -s*x - c*y );
   pv[1][1] = OM * (  c*x - s*y );
   pv[1][2] = 0.0;

/* Finished. */

}