398 lines
12 KiB
JavaScript
398 lines
12 KiB
JavaScript
(function (L, d3, satelliteJs) {
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var RADIANS = Math.PI / 180;
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var DEGREES = 180 / Math.PI;
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var R_EARTH = 6378.137; // equatorial radius (km)
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/* =============================================== */
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/* =============== CLOCK ========================= */
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/* =============================================== */
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/**
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* Factory function for keeping track of elapsed time and rates.
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*/
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function Clock() {
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this._rate = 60; // 1ms elapsed : 60sec simulated
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this._date = d3.now();
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this._elapsed = 0;
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};
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Clock.prototype.date = function (timeInMs) {
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if (!arguments.length) return this._date + (this._elapsed * this._rate);
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this._date = timeInMs;
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return this;
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};
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Clock.prototype.elapsed = function (ms) {
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if (!arguments.length) return this._date - d3.now(); // calculates elapsed
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this._elapsed = ms;
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return this;
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};
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Clock.prototype.rate = function (secondsPerMsElapsed) {
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if (!arguments.length) return this._rate;
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this._rate = secondsPerMsElapsed;
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return this;
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};
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/* ==================================================== */
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/* =============== CONVERSION ========================= */
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/* ==================================================== */
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function satrecToFeature(satrec, date, props) {
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var properties = props || {};
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var positionAndVelocity = satelliteJs.propagate(satrec, date);
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var gmst = satelliteJs.gstime(date);
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var positionGd = satelliteJs.eciToGeodetic(positionAndVelocity.position, gmst);
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properties.height = positionGd.height;
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return {
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type: 'Feature',
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properties: properties,
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geometry: {
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type: 'Point',
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coordinates: [
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positionGd.longitude * DEGREES,
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positionGd.latitude * DEGREES
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]
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}
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};
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};
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/* ==================================================== */
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/* =============== TLE ================================ */
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/* ==================================================== */
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/**
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* Factory function for working with TLE.
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*/
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function TLE() {
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this._properties;
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this._date;
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};
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TLE.prototype._lines = function (arry) {
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return arry.slice(0, 2);
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};
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TLE.prototype.satrecs = function (tles) {
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return tles.map(function (d) {
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return satelliteJs.twoline2satrec.apply(null, this._lines(d));
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});
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};
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TLE.prototype.features = function (tles) {
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var date = this._date || d3.now();
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return tles.map(function (d) {
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var satrec = satelliteJs.twoline2satrec.apply(null, this._lines(d));
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return satrecToFeature(satrec, date, this._properties(d));
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});
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};
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TLE.prototype.lines = function (func) {
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if (!arguments.length) return this._lines;
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this._lines = func;
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return this;
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};
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TLE.prototype.properties = function (func) {
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if (!arguments.length) return this._properties;
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this._properties = func;
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return this;
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};
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TLE.prototype.date = function (ms) {
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if (!arguments.length) return this._date;
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this._date = ms;
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return this;
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};
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/* ==================================================== */
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/* =============== PARSE ============================== */
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/* ==================================================== */
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/**
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* Parses text file string of tle into groups.
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* @return {string[][]} Like [['tle line 1', 'tle line 2'], ...]
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*/
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function parseTle(tleString) {
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// remove last newline so that we can properly split all the lines
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var lines = tleString.replace(/\r?\n$/g, '').split(/\r?\n/);
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return lines.reduce(function (acc, cur, index) {
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if (index % 2 === 0) acc.push([]);
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acc[acc.length - 1].push(cur);
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return acc;
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}, []);
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};
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/* ==================================================== */
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/* =============== SATELLITE ========================== */
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/* ==================================================== */
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/**
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* Satellite factory function that wraps satellitejs functionality
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* and can compute footprints based on TLE and date
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*
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* @param {string[][]} tle two-line element
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* @param {Date} date date to propagate with TLE
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*/
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function Satellite(tle, date) {
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this._satrec = satelliteJs.twoline2satrec(tle[0], tle[1]);
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this._satNum = this._satrec.satnum; // NORAD Catalog Number
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this._altitude; // km
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this._position = {
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lat: null,
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lng: null
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};
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this._halfAngle; // degrees
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this._date;
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this._gmst;
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this.setDate(date);
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this.update();
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this._orbitType = this.orbitTypeFromAlt(this._altitude); // LEO, MEO, or GEO
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};
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/**
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* Updates satellite position and altitude based on current TLE and date
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*/
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Satellite.prototype.update = function () {
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var positionAndVelocity = satelliteJs.propagate(this._satrec, this._date);
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var positionGd = satelliteJs.eciToGeodetic(positionAndVelocity.position, this._gmst);
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this._position = {
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lat: positionGd.latitude * DEGREES,
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lng: positionGd.longitude * DEGREES
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};
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this._altitude = positionGd.height;
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return this;
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};
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/**
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* @returns {GeoJSON.Polygon} GeoJSON describing the satellite's current footprint on the Earth
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*/
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Satellite.prototype.getFootprint = function () {
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var theta = this._halfAngle * RADIANS;
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coreAngle = this._coreAngle(theta, this._altitude, R_EARTH) * DEGREES;
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return d3.geoCircle()
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.center([this._position.lng, this._position.lat])
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.radius(coreAngle)();
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};
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/**
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* A conical satellite with half angle casts a circle on the Earth. Find the angle
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* from the center of the earth to the radius of this circle
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* @param {number} theta: Satellite half angle in radians
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* @param {number} altitude Satellite altitude
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* @param {number} r Earth radius
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* @returns {number} core angle in radians
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*/
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Satellite.prototype._coreAngle = function (theta, altitude, r) {
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// if FOV is larger than Earth, assume it goes to the tangential point
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if (Math.sin(theta) > r / (altitude + r)) {
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return Math.acos(r / (r + altitude));
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}
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return Math.abs(Math.asin((r + altitude) * Math.sin(theta) / r)) - theta;
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};
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Satellite.prototype.halfAngle = function (halfAngle) {
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if (!arguments.length) return this._halfAngle;
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this._halfAngle = halfAngle;
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return this;
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};
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Satellite.prototype.satNum = function (satNum) {
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if (!arguments.length) return this._satNum;
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this._satNum = satNum;
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return this;
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};
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Satellite.prototype.altitude = function (altitude) {
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if (!arguments.length) return this._altitude;
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this._altitude = altitude;
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return this;
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};
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Satellite.prototype.position = function (position) {
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if (!arguments.length) return this._position;
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this._position = position;
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return this;
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};
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Satellite.prototype.getOrbitType = function () {
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return this._orbitType;
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};
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/**
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* sets both the date and the Greenwich Mean Sidereal Time
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* @param {Date} date
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*/
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Satellite.prototype.setDate = function (date) {
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this._date = date;
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this._gmst = satelliteJs.gstime(date);
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return this;
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};
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/**
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* Maps an altitude to a type of satellite
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* @param {number} altitude (in KM)
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* @returns {'LEO' | 'MEO' | 'GEO'}
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*/
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Satellite.prototype.orbitTypeFromAlt = function (altitude) {
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this._altitude = altitude || this._altitude;
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return this._altitude < 1200 ? 'LEO' : this._altitude > 22000 ? 'GEO' : 'MEO';
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};
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/* =============================================== */
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/* =================== GLOBE ===================== */
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/* =============================================== */
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// Approximate date the tle data was aquired from https://www.space-track.org/#recent
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var TLE_DATA_DATE = new Date(2018, 0, 26).getTime();
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var activeClock;
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var sats;
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var svg = d3.select('#globe');
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var marginTop = 20;
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var width = svg.attr('width');
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var height = svg.attr('height') - marginTop;
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var projection = d3.geoOrthographic()
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.scale((height - 10) / 2)
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.translate([width / 2, height / 2 + marginTop])
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.precision(0.1);
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var geoPath = d3.geoPath()
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.projection(projection);
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svg.append('path')
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.datum({
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type: 'Sphere'
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})
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.style('cursor', 'grab')
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.attr('fill', '#2E86AB')
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.attr('d', geoPath);
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function initGlobe() {
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d3.json('world-110m.json').then(function (worldData) {
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svg.selectAll('.segment')
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.data(topojson.feature(worldData, worldData.objects.countries).features)
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.enter().append('path')
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.style('cursor', 'grab')
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.attr('class', 'segment')
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.attr('d', geoPath)
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.style('stroke', '#888')
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.style('stroke-width', '1px')
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.style('fill', '#e5e5e5')
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.style('opacity', '.4');
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});
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}
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function updateSats(date) {
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sats.forEach(function (sat) {
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return sat.setDate(date).update()
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});
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return sats
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};
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/**
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* Create satellite objects for each record in the TLEs and begin animation
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* @param {string[][]} parsedTles
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*/
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function initSats(parsedTles) {
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activeClock = new Clock()
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.rate(100)
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.date(TLE_DATA_DATE);
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sats = parsedTles.map(function (tle) {
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var sat = new Satellite(tle, new Date(2018, 0, 26));
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//61.73 degree half angle corresponds to 3 degree coverage angle, obviously
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//this is far less than we intend to provide but it works well for this graphic.
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sat.halfAngle(61.73);
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return sat;
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});
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window.requestAnimationFrame(animateSats);
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return sats;
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};
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function draw() {
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redrawGlobe();
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svg.selectAll('.footprint')
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.data(sats, function (sat) {
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return sat.satNum();
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})
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.join(
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function (enter) {
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return enter.append('path')
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.attr('class', function (sat) {
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return 'footprint footprint--' + sat.getOrbitType()
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})
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.style('cursor', 'grab');
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}
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).attr('d', function (sat) {
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return geoPath(sat.getFootprint());
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});
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};
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function redrawGlobe() {
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svg.selectAll('.segment')
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.attr('d', geoPath);
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}
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var m0;
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var o0;
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function mousedown() {
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m0 = [d3.event.pageX, d3.event.pageY];
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o0 = projection.rotate();
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d3.event.preventDefault();
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};
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function mousemove() {
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if (m0) {
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var m1 = [d3.event.pageX, d3.event.pageY];
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const o1 = [o0[0] + (m1[0] - m0[0]) / 6, o0[1] + (m0[1] - m1[1]) / 6];
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projection.rotate(o1);
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draw();
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}
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};
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function mouseup() {
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if (m0) {
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mousemove();
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m0 = null;
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}
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}
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svg.on('mousedown', mousedown);
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d3.select(window)
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.on('mousemove', mousemove)
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.on('mouseup', mouseup);
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function animateSats(elapsed) {
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var dateInMs = activeClock.elapsed(elapsed)
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.date();
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var date = new Date(dateInMs);
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svg.select('.date-counter').text('' + date);
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updateSats(date);
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draw();
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window.requestAnimationFrame(animateSats);
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}
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initGlobe();
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// WARNING: THE TLES HERE ARE NOT REAL NORAD-PUBLISHED TLES - THE TLE FORMAT
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// IS USED ONLY AS A WAY TO SPECIFY THE ORBITS IN THE CONSTELLATION.
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d3.text('tles.txt')
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.then(parseTle)
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.then(initSats);
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}(window.L, window.d3, window.satellite)) |