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.
*/
import { DEG2RAD, Earth, MILLISECONDS_TO_DAYS, PI, RAD2DEG, Sgp4, TAU, } from '../main.js';
/**
* Converts ECF to ECI coordinates.
*
* [X] [C -S 0][X]
* [Y] = [S C 0][Y]
* [Z]eci [0 0 1][Z]ecf
* @param ecf takes xyz coordinates
* @param gmst takes a number in gmst time
* @returns array containing eci coordinates
*/
export function ecf2eci(ecf, gmst) {
const X = (ecf.x * Math.cos(gmst) - ecf.y * Math.sin(gmst));
const Y = (ecf.x * Math.sin(gmst) + ecf.y * Math.cos(gmst));
const Z = ecf.z;
return { x: X, y: Y, z: Z };
}
/**
* Converts ECEF coordinates to ENU coordinates.
* @param ecf - The ECEF coordinates.
* @param lla - The LLA coordinates.
* @returns The ENU coordinates.
*/
export function ecf2enu(ecf, lla) {
const { lat, lon } = lla;
const { x, y, z } = ecf;
const e = (-Math.sin(lon) * x + Math.cos(lon) * y);
const n = (-Math.sin(lat) * Math.cos(lon) * x - Math.sin(lat) * Math.sin(lon) * y + Math.cos(lat) * z);
const u = (Math.cos(lat) * Math.cos(lon) * x + Math.cos(lat) * Math.sin(lon) * y + Math.sin(lat) * z);
return { x: e, y: n, z: u };
}
/**
* Converts ECI to ECF coordinates.
*
* [X] [C -S 0][X]
* [Y] = [S C 0][Y]
* [Z]eci [0 0 1][Z]ecf
*
* Inverse:
* [X] [C S 0][X]
* [Y] = [-S C 0][Y]
* [Z]ecf [0 0 1][Z]eci
* @param eci takes xyz coordinates
* @param gmst takes a number in gmst time
* @returns array containing ecf coordinates
*/
export function eci2ecf(eci, gmst) {
const x = (eci.x * Math.cos(gmst) + eci.y * Math.sin(gmst));
const y = (eci.x * -Math.sin(gmst) + eci.y * Math.cos(gmst));
const z = eci.z;
return {
x,
y,
z,
};
}
/**
* EciToGeodetic converts eci coordinates to lla coordinates
* @variation cached - results are cached
* @param eci takes xyz coordinates
* @param gmst takes a number in gmst time
* @returns array containing lla coordinates
*/
export function eci2lla(eci, gmst) {
// http://www.celestrak.com/columns/v02n03/
const a = 6378.137;
const b = 6356.7523142;
const R = Math.sqrt(eci.x * eci.x + eci.y * eci.y);
const f = (a - b) / a;
const e2 = 2 * f - f * f;
let lon = Math.atan2(eci.y, eci.x) - gmst;
while (lon < -PI) {
lon += TAU;
}
while (lon > PI) {
lon -= TAU;
}
const kmax = 20;
let k = 0;
let lat = Math.atan2(eci.z, Math.sqrt(eci.x * eci.x + eci.y * eci.y));
let C = 0;
while (k < kmax) {
C = 1 / Math.sqrt(1 - e2 * (Math.sin(lat) * Math.sin(lat)));
lat = Math.atan2(eci.z + a * C * e2 * Math.sin(lat), R);
k += 1;
}
const alt = R / Math.cos(lat) - a * C;
lon = (lon * RAD2DEG);
lat = (lat * RAD2DEG);
return { lon: lon, lat: lat, alt: alt };
}
/**
* Converts geodetic coordinates (longitude, latitude, altitude) to Earth-Centered Earth-Fixed (ECF) coordinates.
* @param lla The geodetic coordinates in radians and meters.
* @returns The ECF coordinates in meters.
*/
export function llaRad2ecf(lla) {
const { lon, lat, alt } = lla;
const a = 6378.137;
const b = 6356.7523142;
const f = (a - b) / a;
const e2 = 2 * f - f * f;
const normal = a / Math.sqrt(1 - e2 * Math.sin(lat) ** 2);
const x = (normal + alt) * Math.cos(lat) * Math.cos(lon);
const y = (normal + alt) * Math.cos(lat) * Math.sin(lon);
const z = (normal * (1 - e2) + alt) * Math.sin(lat);
return {
x: x,
y: y,
z: z,
};
}
/**
* Converts geodetic coordinates (longitude, latitude, altitude) to Earth-Centered Earth-Fixed (ECF) coordinates.
* @param lla The geodetic coordinates in degrees and meters.
* @returns The ECF coordinates in meters.
*/
export function lla2ecf(lla) {
const { lon, lat, alt } = lla;
const lonRad = lon * DEG2RAD;
const latRad = lat * DEG2RAD;
return llaRad2ecf({
lon: lonRad,
lat: latRad,
alt,
});
}
/**
* Converts geodetic coordinates (latitude, longitude, altitude) to Earth-centered inertial (ECI) coordinates.
* @variation cached - results are cached
* @param lla The geodetic coordinates in radians and meters.
* @param gmst The Greenwich Mean Sidereal Time in seconds.
* @returns The ECI coordinates in meters.
*/
export function lla2eci(lla, gmst) {
const { lat, lon, alt } = lla;
const cosLat = Math.cos(lat);
const sinLat = Math.sin(lat);
const cosLon = Math.cos(lon + gmst);
const sinLon = Math.sin(lon + gmst);
const x = (Earth.radiusMean + alt) * cosLat * cosLon;
const y = (Earth.radiusMean + alt) * cosLat * sinLon;
const z = (Earth.radiusMean + alt) * sinLat;
return { x, y, z };
}
/**
* Calculates Geodetic Lat Lon Alt to ECEF coordinates.
* @deprecated This needs to be validated.
* @param lla The geodetic coordinates in degrees and meters.
* @returns The ECEF coordinates in meters.
*/
export function lla2ecef(lla) {
const { lat, lon, alt } = lla;
const a = 6378.137; // semi-major axis length in meters according to the WGS84
const b = 6356.752314245; // semi-minor axis length in meters according to the WGS84
const e = Math.sqrt(1 - b ** 2 / a ** 2); // eccentricity
const N = a / Math.sqrt(1 - e ** 2 * Math.sin(lat) ** 2); // radius of curvature in the prime vertical
const x = ((N + alt) * Math.cos(lat) * Math.cos(lon));
const y = ((N + alt) * Math.cos(lat) * Math.sin(lon));
const z = ((N * (1 - e ** 2) + alt) * Math.sin(lat));
return { x, y, z };
}
/**
* Converts LLA to SEZ coordinates.
* @see http://www.celestrak.com/columns/v02n02/
* @param lla The LLA coordinates.
* @param ecf The ECF coordinates.
* @returns The SEZ coordinates.
*/
export function lla2sez(lla, ecf) {
const lon = lla.lon;
const lat = lla.lat;
const observerEcf = llaRad2ecf({
lat,
lon,
alt: 0,
});
const rx = ecf.x - observerEcf.x;
const ry = ecf.y - observerEcf.y;
const rz = ecf.z - observerEcf.z;
// Top is short for topocentric
const south = Math.sin(lat) * Math.cos(lon) * rx + Math.sin(lat) * Math.sin(lon) * ry - Math.cos(lat) * rz;
const east = -Math.sin(lon) * rx + Math.cos(lon) * ry;
const zenith = Math.cos(lat) * Math.cos(lon) * rx + Math.cos(lat) * Math.sin(lon) * ry + Math.sin(lat) * rz;
return { s: south, e: east, z: zenith };
}
/**
* Converts a vector in Right Ascension, Elevation, and Range (RAE) coordinate system
* to a vector in South, East, and Zenith (SEZ) coordinate system.
* @param rae The vector in RAE coordinate system.
* @returns The vector in SEZ coordinate system.
*/
export function rae2sez(rae) {
const south = -rae.rng * Math.cos(rae.el) * Math.cos(rae.az);
const east = rae.rng * Math.cos(rae.el) * Math.sin(rae.az);
const zenith = rae.rng * Math.sin(rae.el);
return {
s: south,
e: east,
z: zenith,
};
}
/**
* Converts a vector in Right Ascension, Elevation, and Range (RAE) coordinate system
* to Earth-Centered Fixed (ECF) coordinate system.
* @template D - The dimension of the RAE vector.
* @template A - The dimension of the LLA vector.
* @param rae - The vector in RAE coordinate system.
* @param lla - The vector in LLA coordinate system.
* @returns The vector in ECF coordinate system.
*/
export function rae2ecf(rae, lla) {
const llaRad = {
lat: (lla.lat * DEG2RAD),
lon: (lla.lon * DEG2RAD),
alt: lla.alt,
};
const raeRad = {
az: (rae.az * DEG2RAD),
el: (rae.el * DEG2RAD),
rng: rae.rng,
};
const obsEcf = llaRad2ecf(llaRad);
const sez = rae2sez(raeRad);
// Some needed calculations
const slat = Math.sin(llaRad.lat);
const slon = Math.sin(llaRad.lon);
const clat = Math.cos(llaRad.lat);
const clon = Math.cos(llaRad.lon);
const x = slat * clon * sez.s + -slon * sez.e + clat * clon * sez.z + obsEcf.x;
const y = slat * slon * sez.s + clon * sez.e + clat * slon * sez.z + obsEcf.y;
const z = -clat * sez.s + slat * sez.z + obsEcf.z;
return { x, y, z };
}
/**
* Converts a vector from RAE (Range, Azimuth, Elevation) coordinates to ECI (Earth-Centered Inertial) coordinates.
* @variation cached - results are cached
* @param rae The vector in RAE coordinates.
* @param lla The vector in LLA (Latitude, Longitude, Altitude) coordinates.
* @param gmst The Greenwich Mean Sidereal Time.
* @returns The vector in ECI coordinates.
*/
export function rae2eci(rae, lla, gmst) {
const ecf = rae2ecf(rae, lla);
const eci = ecf2eci(ecf, gmst);
return eci;
}
/**
* Converts a vector in RAE (Range, Azimuth, Elevation) coordinates to ENU (East, North, Up) coordinates.
* @param rae - The vector in RAE coordinates.
* @returns The vector in ENU coordinates.
*/
export function rae2enu(rae) {
const e = (rae.rng * Math.cos(rae.el) * Math.sin(rae.az));
const n = (rae.rng * Math.cos(rae.el) * Math.cos(rae.az));
const u = (rae.rng * Math.sin(rae.el));
return { x: e, y: n, z: u };
}
/**
* Converts South, East, and Zenith (SEZ) coordinates to Right Ascension, Elevation, and Range (RAE) coordinates.
* @param sez The SEZ coordinates.
* @returns Rng, Az, El array
*/
export function sez2rae(sez) {
const rng = Math.sqrt(sez.s * sez.s + sez.e * sez.e + sez.z * sez.z);
const el = Math.asin(sez.z / rng);
const az = (Math.atan2(-sez.e, sez.s) + PI);
return { rng, az, el };
}
/**
* Converts Earth-Centered Fixed (ECF) coordinates to Right Ascension (RA),
* Elevation (E), and Azimuth (A) coordinates.
* @param lla The Latitude, Longitude, and Altitude (LLA) coordinates.
* @param ecf The Earth-Centered Fixed (ECF) coordinates.
* @returns The Right Ascension (RA), Elevation (E), and Azimuth (A) coordinates.
*/
export function ecfRad2rae(lla, ecf) {
const sezCoords = lla2sez(lla, ecf);
const rae = sez2rae(sezCoords);
return { rng: rae.rng, az: (rae.az * RAD2DEG), el: (rae.el * RAD2DEG) };
}
/**
* Converts Earth-Centered Fixed (ECF) coordinates to Right Ascension (RA),
* Elevation (E), and Azimuth (A) coordinates.
* @variation cached - results are cached
* @param lla The Latitude, Longitude, and Altitude (LLA) coordinates.
* @param ecf The Earth-Centered Fixed (ECF) coordinates.
* @returns The Right Ascension (RA), Elevation (E), and Azimuth (A) coordinates.
*/
export function ecf2rae(lla, ecf) {
const { lat, lon } = lla;
const latRad = (lat * DEG2RAD);
const lonRad = (lon * DEG2RAD);
const rae = ecfRad2rae({ lat: latRad, lon: lonRad, alt: lla.alt }, ecf);
return rae;
}
export const jday = (year, mon, day, hr, minute, sec) => {
if (typeof year === 'undefined') {
const now = new Date();
const jDayStart = new Date(now.getUTCFullYear(), 0, 0);
const jDayDiff = now.getDate() - jDayStart.getDate();
return Math.floor(jDayDiff / MILLISECONDS_TO_DAYS);
}
if (typeof mon === 'undefined' ||
typeof day === 'undefined' ||
typeof hr === 'undefined' ||
typeof minute === 'undefined' ||
typeof sec === 'undefined') {
throw new Error('Invalid date');
}
return (367.0 * year -
Math.floor(7 * (year + Math.floor((mon + 9) / 12.0)) * 0.25) +
Math.floor((275 * mon) / 9.0) +
day +
1721013.5 +
((sec / 60.0 + minute) / 60.0 + hr) / 24.0);
};
/**
* Calculates the Greenwich Mean Sidereal Time (GMST) for a given date.
* @param date - The date for which to calculate the GMST.
* @returns An object containing the GMST value and the Julian date.
*/
export function calcGmst(date) {
const j = jday(date.getUTCFullYear(), date.getUTCMonth() + 1, date.getUTCDate(), date.getUTCHours(), date.getUTCMinutes(), date.getUTCSeconds()) +
date.getUTCMilliseconds() * MILLISECONDS_TO_DAYS;
const gmst = Sgp4.gstime(j);
return { gmst, j };
}
/**
* Converts ECI coordinates to RAE (Right Ascension, Azimuth, Elevation) coordinates.
* @variation cached - results are cached
* @param now - Current date and time.
* @param eci - ECI coordinates of the satellite.
* @param sensor - Sensor object containing observer's geodetic coordinates.
* @returns Object containing azimuth, elevation and range in degrees and kilometers respectively.
*/
export function eci2rae(now, eci, sensor) {
now = new Date(now);
const { gmst } = calcGmst(now);
const positionEcf = eci2ecf(eci, gmst);
const lla = {
lat: (sensor.lat * DEG2RAD),
lon: (sensor.lon * DEG2RAD),
alt: sensor.alt,
};
const rae = ecfRad2rae(lla, positionEcf);
return rae;
}
/**
* Calculates the inertial azimuth of a satellite given its latitude and inclination.
* @param lat - The latitude of the satellite in degrees.
* @param inc - The inclination of the satellite in degrees.
* @returns The inertial azimuth of the satellite in degrees.
*/
export function calcInertAz(lat, inc) {
const phi = lat * DEG2RAD;
const i = inc * DEG2RAD;
const az = Math.asin(Math.cos(i) / Math.cos(phi));
return (az * RAD2DEG);
}
/**
* Calculates the inclination angle of a satellite from its launch azimuth and latitude.
* @param lat - The latitude of the observer in degrees.
* @param az - The launch azimuth angle of the satellite in degrees clockwise from north.
* @returns The inclination angle of the satellite in degrees.
*/
export function calcIncFromAz(lat, az) {
const phi = lat * DEG2RAD;
const beta = az * DEG2RAD;
const inc = Math.acos(Math.sin(beta) * Math.cos(phi));
return (inc * RAD2DEG);
}
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