ootk-core
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Orbital Object Toolkit. A modern typed replacement for satellite.js including SGP4 propagation, TLE parsing, Sun and Moon calculations, and more.
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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.
*/
/* eslint-disable no-undefined */
import { ITRF } from '../coordinate/ITRF.js';
import { AngularDistanceMethod } from '../enums/AngularDistanceMethod.js';
import { Vector3D } from '../operations/Vector3D.js';
import { DEG2RAD, halfPi, RAD2DEG, TAU } from '../utils/constants.js';
import { angularDistance } from '../utils/functions.js';
// / Range, azimuth, and elevation.
export class RAE {
epoch;
rng;
azRad;
elRad;
rngRate;
azRateRad;
elRateRad;
constructor(epoch, rng, azRad, elRad,
/** The range rate of the satellite relative to the observer in kilometers per second. */
rngRate,
/** The azimuth rate of the satellite relative to the observer in radians per second. */
azRateRad,
/** The elevation rate of the satellite relative to the observer in radians per second. */
elRateRad) {
this.epoch = epoch;
this.rng = rng;
this.azRad = azRad;
this.elRad = elRad;
this.rngRate = rngRate;
this.azRateRad = azRateRad;
this.elRateRad = elRateRad;
// Do nothing
}
// / Create a new [Razel] object, using degrees for the angular values.
static fromDegrees(epoch, range, azimuth, elevation, rangeRate, azimuthRate, elevationRate) {
const azimuthRateRad = azimuthRate ? azimuthRate * DEG2RAD : undefined;
const elevationRateRad = elevationRate ? elevationRate * DEG2RAD : undefined;
return new RAE(epoch, range, (azimuth * DEG2RAD), (elevation * DEG2RAD), rangeRate, azimuthRateRad, elevationRateRad);
}
/**
* Create a [Razel] object from an inertial [state] and [site] vector.
* @param state The inertial [state] vector.
* @param site The observer [site] vector.
* @returns A new [Razel] object.
*/
static fromStateVector(state, site) {
const stateEcef = state.toITRF();
const siteEcef = site.toITRF();
const po2 = halfPi;
const r = stateEcef.position.subtract(siteEcef.position);
const rDot = stateEcef.velocity;
const geo = siteEcef.toGeodetic();
const p = r.rotZ(geo.lon).rotY((po2 - geo.lat));
const pDot = rDot.rotZ(geo.lon).rotY((po2 - geo.lat));
const pS = p.x;
const pE = p.y;
const pZ = p.z;
const pSDot = pDot.x;
const pEDot = pDot.y;
const pZDot = pDot.z;
const pMag = p.magnitude();
const pSEMag = Math.sqrt(pS * pS + pE * pE);
const elevation = Math.asin(pZ / pMag);
let azimuth;
if (elevation !== po2) {
azimuth = Math.atan2(-pE, pS) + Math.PI;
}
else {
azimuth = Math.atan2(-pEDot, pSDot) + Math.PI;
}
const rangeRate = p.dot(pDot) / pMag;
const azimuthRate = (pSDot * pE - pEDot * pS) / (pS * pS + pE * pE);
const elevationRate = (pZDot - rangeRate * Math.sin(elevation)) / pSEMag;
return new RAE(state.epoch, pMag, (azimuth % TAU), elevation, rangeRate, azimuthRate, elevationRate);
}
/**
* Gets the azimuth in degrees.
* @returns The azimuth in degrees.
*/
get az() {
return this.azRad * RAD2DEG;
}
/**
* Gets the elevation angle in degrees.
* @returns The elevation angle in degrees.
*/
get el() {
return this.elRad * RAD2DEG;
}
/**
* Gets the azimuth rate in degrees per second.
* @returns The azimuth rate in degrees per second, or undefined if it is not available.
*/
get azRate() {
return this.azRateRad ? this.azRateRad * RAD2DEG : undefined;
}
/**
* Gets the elevation rate in degrees per second.
* @returns The elevation rate in degrees per second, or undefined if the elevation rate is not set.
*/
get elRate() {
return this.elRateRad ? this.elRateRad * RAD2DEG : undefined;
}
toString() {
return [
'[RazEl]',
` Epoch: ${this.epoch}`,
` Azimuth: ${this.az.toFixed(4)}°`,
` Elevation: ${this.el.toFixed(4)}°`,
` Range: ${this.rng.toFixed(3)} km`,
].join('\n');
}
/**
* Return the position relative to the observer [site].
*
* An optional azimuth [az] _(rad)_ and elevation [el] _(rad)_ value can be
* passed to override the values contained in this observation.
* @param site The observer [site].
* @param azRad Azimuth _(rad)_.
* @param elRad Elevation _(rad)_.
* @returns A [Vector3D] object.
*/
position(site, azRad, elRad) {
const ecef = site.toITRF();
const geo = ecef.toGeodetic();
const po2 = halfPi;
const newAz = azRad ?? this.azRad;
const newEl = elRad ?? this.elRad;
const sAz = Math.sin(newAz);
const cAz = Math.cos(newAz);
const sEl = Math.sin(newEl);
const cEl = Math.cos(newEl);
const pSez = new Vector3D((-this.rng * cEl * cAz), (this.rng * cEl * sAz), (this.rng * sEl));
const rEcef = pSez
.rotY(-(po2 - geo.lat))
.rotZ(-geo.lon)
.add(ecef.position);
return new ITRF(this.epoch, rEcef, Vector3D.origin).toJ2000().position;
}
/**
* Convert this observation into a [J2000] state vector.
*
* This will throw an error if the [rangeRate], [elevationRate], or
* [azimuthRate] are not defined.
* @param site The observer [site].
* @returns A [J2000] state vector.
*/
toStateVector(site) {
// If the rates are not defined then assume stationary
this.rngRate ??= 0;
this.elRateRad ??= 0;
this.azRateRad ??= 0;
const ecef = site.toITRF();
const geo = ecef.toGeodetic();
const po2 = halfPi;
const sAz = Math.sin(this.azRad);
const cAz = Math.cos(this.azRad);
const sEl = Math.sin(this.elRad);
const cEl = Math.cos(this.elRad);
const pSez = new Vector3D((-this.rng * cEl * cAz), (this.rng * cEl * sAz), (this.rng * sEl));
const pDotSez = new Vector3D((-this.rngRate * cEl * cAz +
this.rng * sEl * cAz * this.elRateRad +
this.rng * cEl * sAz * this.azRateRad), (this.rngRate * cEl * sAz -
this.rng * sEl * sAz * this.elRateRad +
this.rng * cEl * cAz * this.azRateRad), (this.rngRate * sEl + this.rng * cEl * this.elRateRad));
const pEcef = pSez.rotY(-(po2 - geo.lat)).rotZ(-geo.lon);
const pDotEcef = pDotSez
.rotY(-(po2 - geo.lat))
// TODO: #13 Intermediate unit type is incorrect.
.rotZ(-geo.lon);
const rEcef = pEcef.add(ecef.position);
return new ITRF(this.epoch, rEcef, pDotEcef).toJ2000();
}
/**
* Calculate the angular distance _(rad)_ between this and another [Razel]
* object.
* @param razel The other [Razel] object.
* @param method The angular distance method to use.
* @returns The angular distance _(rad)_.
*/
angle(razel, method = AngularDistanceMethod.Cosine) {
return angularDistance(this.azRad, this.elRad, razel.azRad, razel.elRad, method);
}
/**
* Calculate the angular distance _(°)_ between this and another [Razel]
* object.
* @param razel The other [Razel] object.
* @param method The angular distance method to use.
* @returns The angular distance _(°)_.
*/
angleDegrees(razel, method = AngularDistanceMethod.Cosine) {
return this.angle(razel, method) * RAD2DEG;
}
}
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