use crate::consts::DAS2R;

use crate::vm::rv2m;

/// FK5 to Hipparcos rotation and spin.

///

/// Status:  support function.

///

/// Returned:

///    r5h   [[f64; 3]; 3] r-matrix: FK5 rotation wrt Hipparcos (Note 2)

///    s5h   [f64; 3]      r-vector: FK5 spin wrt Hipparcos (Note 3)

///

/// Notes:

///

/// 1) This function models the FK5 to Hipparcos transformation as a

///    pure rotation and spin;  zonal errors in the FK5 catalog are not

///    taken into account.

///

/// 2) The r-matrix r5h operates in the sense:

///

///          P_Hipparcos = r5h x P_FK5

///

///    where P_FK5 is a p-vector in the FK5 frame, and P_Hipparcos is

///    the equivalent Hipparcos p-vector.

///

/// 3) The r-vector s5h represents the time derivative of the FK5 to

///    Hipparcos rotation.  The units are radians per year (Julian,

///    TDB).

///

/// Called:

///    rv2m      r-vector to r-matrix

///

/// Reference:

///    F.Mignard & M.Froeschle, Astron.Astrophys., 354, 732-739 (2000).

pub fn fk5hip() -> ([[f64; 3]; 3], [f64; 3]) {

    let mut r5h = [[0.0; 3]; 3];

    let mut s5h = [0.0; 3];

    /* FK5 wrt Hipparcos orientation and spin (radians, radians/year) */

    let epx = -19.9e-3 * DAS2R;

    let epy = -9.1e-3 * DAS2R;

    let epz = 22.9e-3 * DAS2R;

    let omx = -0.30e-3 * DAS2R;

    let omy = 0.60e-3 * DAS2R;

    let omz = 0.70e-3 * DAS2R;

    /* FK5 to Hipparcos orientation expressed as an r-vector. */

    let v = [epx, epy, epz];

    /* Re-express as an r-matrix. */

    rv2m(&v, &mut r5h);

    /* Hipparcos wrt FK5 spin expressed as an r-vector. */

    s5h[0] = omx;

    s5h[1] = omy;

    s5h[2] = omz;

    (r5h, s5h)

}