lox_frames/iers/
polar_motion.rs

1// SPDX-FileCopyrightText: 2025 Helge Eichhorn <git@helgeeichhorn.de>
2//
3// SPDX-License-Identifier: MPL-2.0
4
5use lox_core::glam::DMat3;
6use lox_core::units::Angle;
7use lox_time::{Time, time_scales::Tt};
8
9use crate::iers::{ReferenceSystem, tio::TioLocator};
10
11impl ReferenceSystem {
12    /// Returns the polar motion rotation matrix for the given pole coordinates.
13    pub fn polar_motion_matrix(&self, time: Time<Tt>, pole_coords: PoleCoords) -> DMat3 {
14        if pole_coords.is_zero() {
15            return DMat3::IDENTITY;
16        };
17        match self {
18            ReferenceSystem::Iers1996 => pole_coords.polar_motion_matrix(),
19            ReferenceSystem::Iers2003(_) | ReferenceSystem::Iers2010 => {
20                let sp = TioLocator::iau2000(time);
21                pole_coords.polar_motion_matrix_iau2000(sp)
22            }
23        }
24    }
25}
26
27/// Pole coordinates (xp, yp) describing polar motion.
28#[derive(Debug, Clone, Copy, Default, PartialEq)]
29pub struct PoleCoords {
30    /// x-coordinate of the pole.
31    pub xp: Angle,
32    /// y-coordinate of the pole.
33    pub yp: Angle,
34}
35
36impl PoleCoords {
37    /// Returns the classical polar motion matrix for the pole coordinates.
38    ///
39    /// # References
40    ///
41    /// - SOFA [`pom00`](https://github.com/liberfa/erfa/blob/master/src/pom00.c)
42    pub fn polar_motion_matrix(&self) -> DMat3 {
43        (-self.yp).rotation_x() * (-self.xp).rotation_y()
44    }
45
46    /// Computes the polar motion matrix including the TIO locator s' (IAU 2000+).
47    pub fn polar_motion_matrix_iau2000(&self, sp: TioLocator) -> DMat3 {
48        self.polar_motion_matrix() * sp.0.rotation_z()
49    }
50
51    /// Returns `true` if both pole coordinates are zero.
52    pub fn is_zero(&self) -> bool {
53        self.xp.is_zero() && self.yp.is_zero()
54    }
55}
56
57#[cfg(test)]
58mod tests {
59    use lox_approx::assert_approx_eq;
60    use lox_core::units::AngleUnits;
61
62    use super::*;
63
64    #[test]
65    fn test_polar_motion_matrix_iau2000() {
66        let pole = PoleCoords {
67            xp: 2.55060238e-7.rad(),
68            yp: 1.860359247e-6.rad(),
69        };
70        let sp = TioLocator(-1.367_174_580_728_891_5e-11.rad());
71        let exp = DMat3::from_cols_array(&[
72            0.999_999_999_999_967_5,
73            -1.367_174_580_728_847e-11,
74            2.550_602_379_999_972e-7,
75            1.414_624_947_957_029_7e-11,
76            0.999_999_999_998_269_5,
77            -1.860_359_246_998_866_3e-6,
78            -2.550_602_379_741_215_3e-7,
79            1.860_359_247_002_414e-6,
80            0.999_999_999_998_237,
81        ])
82        .transpose();
83        let act = pole.polar_motion_matrix_iau2000(sp);
84        assert_approx_eq!(act, exp, atol <= 1e-12);
85    }
86}
lox_frames/iers/polar_motion.rs

lox_frames/iers/
polar_motion.rs
