earthtrek-core/src/js/earthtrek-satellite.js

Global Nominee NASA Space Apps Challenge 2017 Buenos Aires - Global Finalist (Best Use of Data) NASA Space Apps Challenge 2017 - 1D, 2D, 3D, Go! Challenge

/**
 * @class earthTrekSatellite
 * @module EarthTrek
 * @author SATrek
 * @author Alejandro Sanchez <alejandro.sanchez.trek@gmail.com>
 * @description EarthTrek - NASA Space Apps 2017 12 MAY 2017.
 */

var satellitePropagation = require('./earthtrek-propagation');
var JulianDate = require('cesium/Source/Core/JulianDate');
var Cartesian3 = require('cesium/Source/Core/Cartesian3');
var SampledPositionProperty = require('cesium/Source/DataSources/SampledPositionProperty');
var SampledProperty = require('cesium/Source/DataSources/SampledProperty');

var earthTrekSatellite = earthTrekSatellite || {};

earthTrekSatellite.calculatePosition = function(tleLine1, tleLine2, startTime, date, deltaStep, since) {
    date.setSeconds(date.getSeconds() + deltaStep)
    var propagate = satellitePropagation.getPositionAndVelocity(tleLine1, tleLine2, date);
    var newPosition = propagate.position;
    var samplePosition = {};
    samplePosition.time = JulianDate.addSeconds(startTime, since, new JulianDate());
    samplePosition.position = Cartesian3.fromDegrees(newPosition.longitude, newPosition.latitude, newPosition.height);
    samplePosition.height = newPosition.height;
    samplePosition.velocity = propagate.velocity;
    return samplePosition;
}

earthTrekSatellite.calculatePositions = function(tleLine1, tleLine2, startTime, duration, frequency, date) {
    var deltaStep = duration / (frequency > 0 ? frequency : 1);
    var positions = [];
    positions.times = [];
    positions.positions = [];
    positions.heights = [];
    positions.velocities = [];
    for (var since = 0; since <= duration; since += deltaStep) {
        var samplePosition = this.calculatePosition(tleLine1, tleLine2, startTime, date, deltaStep, since);
        positions.times.push(samplePosition.time);
        positions.positions.push(samplePosition.position);
        positions.heights.push(samplePosition.height);
        positions.velocities.push(samplePosition.velocity);
    }
    return positions;
}

earthTrekSatellite.getSamples = function(tleLine1, tleLine2, startTime, duration, frequency) {

    var previousDate = new Date(JulianDate.toIso8601(startTime));
    previousDate.setSeconds(previousDate.getSeconds() - duration);
    var previousTimeJulian = JulianDate.fromDate(previousDate);
    var previousPositions  = this.calculatePositions(tleLine1, tleLine2, previousTimeJulian, duration, frequency, previousDate);

    var positions = new SampledPositionProperty();
    positions.addSamples(
        previousPositions.times,
        previousPositions.positions
    );

    var heights = new SampledProperty(Number);
    heights.addSamples(
        previousPositions.times,
        previousPositions.heights
    );

    var velocities = new SampledPositionProperty();
    velocities.addSamples(
        previousPositions.times,
        previousPositions.velocities
    );

    var currentDate = new Date(JulianDate.toIso8601(startTime));
    var latestPositions  = this.calculatePositions(tleLine1, tleLine2, startTime, duration, frequency, currentDate);
    positions.addSamples(
        latestPositions.times,
        latestPositions.positions
    );
    heights.addSamples(
        latestPositions.times,
        latestPositions.heights
    );

    velocities.addSamples(
        latestPositions.times,
        latestPositions.velocities
    );
    return {positions: positions, heights: heights, velocities: velocities};
}

earthTrekSatellite.addSamples = function(times, values) {
    var property = new SampledPositionProperty();
    property.addSamples(times, values);
    return property;
}

module.exports = earthTrekSatellite;