ootk-core
Version:
Orbital Object Toolkit. A modern typed replacement for satellite.js including SGP4 propagation, TLE parsing, Sun and Moon calculations, and more.
120 lines • 4.6 kB
JavaScript
/**
* @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 { Earth } from '../body/Earth.js';
import { ITRF } from './ITRF.js';
import { StateVector } from './StateVector.js';
import { TEME } from './TEME.js';
/**
* Represents a position and velocity in the J2000 coordinate system. This is an Earth-centered inertial (ECI)
* coordinate system.
*
* Commonly used ECI frame is defined with the Earth's Mean Equator and Mean Equinox (MEME) at 12:00 Terrestrial Time on
* 1 January 2000. It can be referred to as J2K, J2000 or EME2000. The x-axis is aligned with the mean vernal equinox.
* The z-axis is aligned with the Earth's rotation axis (or equivalently, the celestial North Pole) as it was at that
* time. The y-axis is rotated by 90° East about the celestial equator.
* @see https://en.wikipedia.org/wiki/Earth-centered_inertial
*/
export class J2000 extends StateVector {
/**
* Creates a J2000 coordinate from classical elements.
* @param elements The classical elements.
* @returns The J2000 coordinate.
*/
static fromClassicalElements(elements) {
const rv = elements.toPositionVelocity();
return new J2000(elements.epoch, rv.position, rv.velocity);
}
/**
* Gets the name of the coordinate system.
* @returns The name of the coordinate system.
*/
get name() {
return 'J2000';
}
/**
* Gets a value indicating whether the coordinate system is inertial.
* @returns A boolean value indicating whether the coordinate system is inertial.
*/
get inertial() {
return true;
}
/**
* Converts the coordinates from J2000 to the International Terrestrial Reference Frame (ITRF).
* This is an ECI to ECF transformation.
* @returns The ITRF coordinates.
*/
toITRF() {
const p = Earth.precession(this.epoch);
const n = Earth.nutation(this.epoch);
const ast = (this.epoch.gmstAngle() + n.eqEq);
const rMOD = this.position
.rotZ(-p.zeta)
.rotY(p.theta)
.rotZ(-p.zed);
const vMOD = this.velocity
.rotZ(-p.zeta)
.rotY(p.theta)
.rotZ(-p.zed);
const rTOD = rMOD
.rotX(n.mEps)
.rotZ(-n.dPsi)
.rotX(-n.eps);
const vTOD = vMOD
.rotX(n.mEps)
.rotZ(-n.dPsi)
.rotX(-n.eps);
const rPEF = rTOD.rotZ(ast);
const vPEF = vTOD.rotZ(ast).add(Earth.rotation.negate().cross(rPEF));
return new ITRF(this.epoch, rPEF, vPEF);
}
/**
* Converts the J2000 coordinate to the TEME coordinate.
* @returns The TEME coordinate.
*/
toTEME() {
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(-p.zeta)
.rotY(p.theta)
.rotZ(-p.zed);
const vMOD = this.velocity
.rotZ(-p.zeta)
.rotY(p.theta)
.rotZ(-p.zed);
const rTEME = rMOD
.rotX(n.mEps)
.rotZ(-n.dPsi)
.rotX(-eps)
.rotZ(dPsiCosEps);
const vTEME = vMOD
.rotX(n.mEps)
.rotZ(-n.dPsi)
.rotX(-eps)
.rotZ(dPsiCosEps);
return new TEME(this.epoch, rTEME, vTEME);
}
}
//# sourceMappingURL=J2000.js.map