ootk-core/src/coordinate/TEME.ts

Orbital Object Toolkit. A modern typed replacement for satellite.js including SGP4 propagation, TLE parsing, Sun and Moon calculations, and more.

/**
 * @author Theodore Kruczek.
 * @license MIT
 * @copyright (c) 2022-2025 Theodore Kruczek Permission is
 * hereby granted, free of charge, to any person obtaining a copy of this
 * software and associated documentation files (the "Software"), to deal in the
 * Software without restriction, including without limitation the rights to use,
 * copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
 * the Software, and to permit persons to whom the Software is furnished to do
 * so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */

import { Kilometers, KilometersPerSecond, Radians, Vector3D } from '../main.js';
import { Earth } from '../body/Earth.js';
import type { ClassicalElements } from './ClassicalElements.js';
import { J2000 } from './J2000.js';
import { StateVector } from './StateVector.js';

/**
 * True Equator Mean Equinox (TEME) is a coordinate system commonly used in satellite tracking and orbit prediction. It
 * is a reference frame that defines the position and orientation of an object relative to the Earth's equator and
 * equinox.
 *
 * By using the True Equator Mean Equinox (TEME) coordinate system, we can accurately describe the position and motion
 * of satellites relative to the Earth's equator and equinox. This is particularly useful for tracking and predicting
 * satellite orbits in various applications, such as satellite communication, navigation, and remote sensing.
 */
export class TEME extends StateVector {
  /**
   * Gets the name of the coordinate system.
   * @returns The name of the coordinate system.
   */
  get name(): string {
    return 'TEME';
  }

  /**
   * Gets a value indicating whether the coordinate is inertial.
   * @returns A boolean value indicating whether the coordinate is inertial.
   */
  get inertial(): boolean {
    return true;
  }

  /**
   * Creates a TEME (True Equator Mean Equinox) object from classical orbital elements.
   * @param elements - The classical orbital elements.
   * @returns A new TEME object.
   */
  static fromClassicalElements(elements: ClassicalElements): TEME {
    const rv = elements.toPositionVelocity();

    return new TEME(elements.epoch, rv.position, rv.velocity);
  }

  /**
   * Converts the TEME (True Equator Mean Equinox) coordinates to J2000 coordinates.
   * @returns The J2000 coordinates.
   */
  toJ2000(): J2000 {
    const p = Earth.precession(this.epoch);
    const n = Earth.nutation(this.epoch);
    const eps = n.mEps + n.dEps;
    const dPsiCosEps = n.dPsi * Math.cos(eps);
    const rMOD = this.position
      .rotZ(-dPsiCosEps as Radians)
      .rotX(eps)
      .rotZ(n.dPsi)
      .rotX(-n.mEps);
    const vMOD = this.velocity
      .rotZ(-dPsiCosEps as Radians)
      .rotX(eps)
      .rotZ(n.dPsi)
      .rotX(-n.mEps);
    const rJ2K = rMOD
      .rotZ(p.zed)
      .rotY(-p.theta as Radians)
      .rotZ(p.zeta) as Vector3D<Kilometers>;
    const vJ2K = vMOD
      .rotZ(p.zed)
      .rotY(-p.theta as Radians)
      .rotZ(p.zeta) as Vector3D<KilometersPerSecond>;

    return new J2000(this.epoch, rJ2K, vJ2K);
  }
}