ba1212361f
Commit the previously-untracked standard directories and catalog them in the
root README alongside proof:
- aac/ — communication cargo class: portable boards + a ten-level
offline-first cascade (Apache-2.0 code / CC-BY-4.0 spec).
- map/ — geospatial cargo class: range-requestable signed tilesets +
an F0–F4 fidelity cascade (Apache-2.0 code / CC-BY-4.0 spec).
- sandbox/— isolated, metered, attested execution across the heterogeneous
compute fabric (Apache-2.0 code / CC-BY-4.0 spec).
- jouleclaw-otel-authz, jouleclaw-trust — new jouleclaw reference crates.
Root README now lists aac, map, sandbox, and proof in the catalog, the tree,
and the contribution guide.
Co-Authored-By: Claude Opus 4.8 <[email protected]>
114 lines
3 KiB
Rust
114 lines
3 KiB
Rust
//! ECI (TEME) to ECEF coordinate transform.
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//!
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//! Rotates from the True Equator Mean Equinox (TEME) frame used by
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//! SGP4 to the Earth-Centered Earth-Fixed (ECEF) frame using the
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//! Greenwich Mean Sidereal Time (GMST) rotation.
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use serde::{Deserialize, Serialize};
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use crate::julian::gmst;
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use crate::sgp4::EciPosition;
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/// Position in the Earth-Centered Earth-Fixed (ECEF) frame.
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#[derive(Debug, Clone, Copy, Serialize, Deserialize)]
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pub struct EcefPosition {
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/// X position (km).
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pub x: f64,
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/// Y position (km).
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pub y: f64,
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/// Z position (km).
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pub z: f64,
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}
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/// Rotate an ECI (TEME) position to ECEF using the GMST at the given Julian Date.
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///
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/// The TEME-to-ECEF rotation is a simple Z-axis rotation by -GMST:
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/// ```text
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/// ecef_x = eci_x * cos(gmst) + eci_y * sin(gmst)
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/// ecef_y = -eci_x * sin(gmst) + eci_y * cos(gmst)
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/// ecef_z = eci_z
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/// ```
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pub fn eci_to_ecef(eci: &EciPosition, jd: f64) -> EcefPosition {
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let theta = gmst(jd);
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let cos_theta = theta.cos();
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let sin_theta = theta.sin();
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EcefPosition {
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x: eci.x * cos_theta + eci.y * sin_theta,
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y: -eci.x * sin_theta + eci.y * cos_theta,
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z: eci.z,
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}
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}
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/// Rotate an ECEF position to ECI (TEME) at the given Julian Date.
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///
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/// Inverse of [`eci_to_ecef`].
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pub fn ecef_to_eci(ecef: &EcefPosition, jd: f64) -> EciPosition {
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let theta = gmst(jd);
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let cos_theta = theta.cos();
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let sin_theta = theta.sin();
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EciPosition {
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x: ecef.x * cos_theta - ecef.y * sin_theta,
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y: ecef.x * sin_theta + ecef.y * cos_theta,
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z: ecef.z,
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vx: 0.0,
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vy: 0.0,
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vz: 0.0,
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}
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}
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#[cfg(test)]
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mod tests {
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use super::*;
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#[test]
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fn test_ecef_roundtrip() {
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let eci = EciPosition {
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x: 6500.0,
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y: 1000.0,
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z: 3000.0,
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vx: 0.0,
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vy: 0.0,
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vz: 0.0,
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};
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let jd = 2451545.0; // J2000.0
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let ecef = eci_to_ecef(&eci, jd);
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let eci2 = ecef_to_eci(&ecef, jd);
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assert!((eci.x - eci2.x).abs() < 1e-9, "x: {} vs {}", eci.x, eci2.x);
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assert!((eci.y - eci2.y).abs() < 1e-9, "y: {} vs {}", eci.y, eci2.y);
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assert!((eci.z - eci2.z).abs() < 1e-9, "z: {} vs {}", eci.z, eci2.z);
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}
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#[test]
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fn test_ecef_z_unchanged() {
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let eci = EciPosition {
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x: 1000.0,
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y: 2000.0,
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z: 5000.0,
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vx: 0.0,
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vy: 0.0,
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vz: 0.0,
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};
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let ecef = eci_to_ecef(&eci, 2451545.0);
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assert!((eci.z - ecef.z).abs() < 1e-12);
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}
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#[test]
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fn test_ecef_preserves_magnitude() {
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let eci = EciPosition {
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x: 6500.0,
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y: 1000.0,
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z: 3000.0,
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vx: 0.0,
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vy: 0.0,
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vz: 0.0,
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};
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let ecef = eci_to_ecef(&eci, 2460000.0);
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let r_eci = (eci.x * eci.x + eci.y * eci.y + eci.z * eci.z).sqrt();
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let r_ecef = (ecef.x * ecef.x + ecef.y * ecef.y + ecef.z * ecef.z).sqrt();
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assert!((r_eci - r_ecef).abs() < 1e-9);
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}
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}
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