271 lines
10 KiB
JavaScript
271 lines
10 KiB
JavaScript
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define([
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'../ThirdParty/when',
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'./buildModuleUrl',
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'./defaultValue',
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'./defined',
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'./Iau2006XysSample',
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'./JulianDate',
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'./Resource',
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'./TimeStandard'
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], function(
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when,
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buildModuleUrl,
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defaultValue,
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defined,
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Iau2006XysSample,
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JulianDate,
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Resource,
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TimeStandard) {
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'use strict';
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/**
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* A set of IAU2006 XYS data that is used to evaluate the transformation between the International
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* Celestial Reference Frame (ICRF) and the International Terrestrial Reference Frame (ITRF).
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*
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* @alias Iau2006XysData
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* @constructor
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*
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* @param {Object} [options] Object with the following properties:
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* @param {Resource|String} [options.xysFileUrlTemplate='Assets/IAU2006_XYS/IAU2006_XYS_{0}.json'] A template URL for obtaining the XYS data. In the template,
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* `{0}` will be replaced with the file index.
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* @param {Number} [options.interpolationOrder=9] The order of interpolation to perform on the XYS data.
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* @param {Number} [options.sampleZeroJulianEphemerisDate=2442396.5] The Julian ephemeris date (JED) of the
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* first XYS sample.
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* @param {Number} [options.stepSizeDays=1.0] The step size, in days, between successive XYS samples.
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* @param {Number} [options.samplesPerXysFile=1000] The number of samples in each XYS file.
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* @param {Number} [options.totalSamples=27426] The total number of samples in all XYS files.
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*
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* @private
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*/
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function Iau2006XysData(options) {
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options = defaultValue(options, defaultValue.EMPTY_OBJECT);
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this._xysFileUrlTemplate = Resource.createIfNeeded(options.xysFileUrlTemplate);
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this._interpolationOrder = defaultValue(options.interpolationOrder, 9);
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this._sampleZeroJulianEphemerisDate = defaultValue(options.sampleZeroJulianEphemerisDate, 2442396.5);
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this._sampleZeroDateTT = new JulianDate(this._sampleZeroJulianEphemerisDate, 0.0, TimeStandard.TAI);
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this._stepSizeDays = defaultValue(options.stepSizeDays, 1.0);
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this._samplesPerXysFile = defaultValue(options.samplesPerXysFile, 1000);
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this._totalSamples = defaultValue(options.totalSamples, 27426);
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this._samples = new Array(this._totalSamples * 3);
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this._chunkDownloadsInProgress = [];
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var order = this._interpolationOrder;
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// Compute denominators and X values for interpolation.
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var denom = this._denominators = new Array(order + 1);
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var xTable = this._xTable = new Array(order + 1);
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var stepN = Math.pow(this._stepSizeDays, order);
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for ( var i = 0; i <= order; ++i) {
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denom[i] = stepN;
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xTable[i] = i * this._stepSizeDays;
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for ( var j = 0; j <= order; ++j) {
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if (j !== i) {
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denom[i] *= (i - j);
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}
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}
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denom[i] = 1.0 / denom[i];
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}
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// Allocate scratch arrays for interpolation.
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this._work = new Array(order + 1);
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this._coef = new Array(order + 1);
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}
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var julianDateScratch = new JulianDate(0, 0.0, TimeStandard.TAI);
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function getDaysSinceEpoch(xys, dayTT, secondTT) {
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var dateTT = julianDateScratch;
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dateTT.dayNumber = dayTT;
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dateTT.secondsOfDay = secondTT;
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return JulianDate.daysDifference(dateTT, xys._sampleZeroDateTT);
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}
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/**
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* Preloads XYS data for a specified date range.
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*
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* @param {Number} startDayTT The Julian day number of the beginning of the interval to preload, expressed in
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* the Terrestrial Time (TT) time standard.
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* @param {Number} startSecondTT The seconds past noon of the beginning of the interval to preload, expressed in
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* the Terrestrial Time (TT) time standard.
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* @param {Number} stopDayTT The Julian day number of the end of the interval to preload, expressed in
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* the Terrestrial Time (TT) time standard.
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* @param {Number} stopSecondTT The seconds past noon of the end of the interval to preload, expressed in
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* the Terrestrial Time (TT) time standard.
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* @returns {Promise} A promise that, when resolved, indicates that the requested interval has been
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* preloaded.
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*/
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Iau2006XysData.prototype.preload = function(startDayTT, startSecondTT, stopDayTT, stopSecondTT) {
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var startDaysSinceEpoch = getDaysSinceEpoch(this, startDayTT, startSecondTT);
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var stopDaysSinceEpoch = getDaysSinceEpoch(this, stopDayTT, stopSecondTT);
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var startIndex = (startDaysSinceEpoch / this._stepSizeDays - this._interpolationOrder / 2) | 0;
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if (startIndex < 0) {
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startIndex = 0;
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}
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var stopIndex = (stopDaysSinceEpoch / this._stepSizeDays - this._interpolationOrder / 2) | 0 + this._interpolationOrder;
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if (stopIndex >= this._totalSamples) {
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stopIndex = this._totalSamples - 1;
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}
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var startChunk = (startIndex / this._samplesPerXysFile) | 0;
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var stopChunk = (stopIndex / this._samplesPerXysFile) | 0;
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var promises = [];
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for ( var i = startChunk; i <= stopChunk; ++i) {
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promises.push(requestXysChunk(this, i));
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}
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return when.all(promises);
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};
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/**
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* Computes the XYS values for a given date by interpolating. If the required data is not yet downloaded,
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* this method will return undefined.
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*
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* @param {Number} dayTT The Julian day number for which to compute the XYS value, expressed in
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* the Terrestrial Time (TT) time standard.
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* @param {Number} secondTT The seconds past noon of the date for which to compute the XYS value, expressed in
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* the Terrestrial Time (TT) time standard.
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* @param {Iau2006XysSample} [result] The instance to which to copy the interpolated result. If this parameter
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* is undefined, a new instance is allocated and returned.
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* @returns {Iau2006XysSample} The interpolated XYS values, or undefined if the required data for this
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* computation has not yet been downloaded.
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*
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* @see Iau2006XysData#preload
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*/
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Iau2006XysData.prototype.computeXysRadians = function(dayTT, secondTT, result) {
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var daysSinceEpoch = getDaysSinceEpoch(this, dayTT, secondTT);
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if (daysSinceEpoch < 0.0) {
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// Can't evaluate prior to the epoch of the data.
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return undefined;
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}
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var centerIndex = (daysSinceEpoch / this._stepSizeDays) | 0;
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if (centerIndex >= this._totalSamples) {
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// Can't evaluate after the last sample in the data.
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return undefined;
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}
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var degree = this._interpolationOrder;
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var firstIndex = centerIndex - ((degree / 2) | 0);
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if (firstIndex < 0) {
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firstIndex = 0;
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}
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var lastIndex = firstIndex + degree;
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if (lastIndex >= this._totalSamples) {
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lastIndex = this._totalSamples - 1;
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firstIndex = lastIndex - degree;
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if (firstIndex < 0) {
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firstIndex = 0;
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}
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}
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// Are all the samples we need present?
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// We can assume so if the first and last are present
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var isDataMissing = false;
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var samples = this._samples;
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if (!defined(samples[firstIndex * 3])) {
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requestXysChunk(this, (firstIndex / this._samplesPerXysFile) | 0);
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isDataMissing = true;
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}
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if (!defined(samples[lastIndex * 3])) {
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requestXysChunk(this, (lastIndex / this._samplesPerXysFile) | 0);
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isDataMissing = true;
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}
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if (isDataMissing) {
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return undefined;
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}
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if (!defined(result)) {
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result = new Iau2006XysSample(0.0, 0.0, 0.0);
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} else {
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result.x = 0.0;
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result.y = 0.0;
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result.s = 0.0;
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}
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var x = daysSinceEpoch - firstIndex * this._stepSizeDays;
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var work = this._work;
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var denom = this._denominators;
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var coef = this._coef;
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var xTable = this._xTable;
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var i, j;
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for (i = 0; i <= degree; ++i) {
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work[i] = x - xTable[i];
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}
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for (i = 0; i <= degree; ++i) {
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coef[i] = 1.0;
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for (j = 0; j <= degree; ++j) {
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if (j !== i) {
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coef[i] *= work[j];
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}
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}
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coef[i] *= denom[i];
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var sampleIndex = (firstIndex + i) * 3;
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result.x += coef[i] * samples[sampleIndex++];
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result.y += coef[i] * samples[sampleIndex++];
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result.s += coef[i] * samples[sampleIndex];
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}
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return result;
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};
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function requestXysChunk(xysData, chunkIndex) {
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if (xysData._chunkDownloadsInProgress[chunkIndex]) {
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// Chunk has already been requested.
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return xysData._chunkDownloadsInProgress[chunkIndex];
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}
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var deferred = when.defer();
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xysData._chunkDownloadsInProgress[chunkIndex] = deferred;
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var chunkUrl;
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var xysFileUrlTemplate = xysData._xysFileUrlTemplate;
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if (defined(xysFileUrlTemplate)) {
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chunkUrl = xysFileUrlTemplate.getDerivedResource({
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templateValues: {
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'0': chunkIndex
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}
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});
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} else {
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chunkUrl = new Resource({
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url : buildModuleUrl('Assets/IAU2006_XYS/IAU2006_XYS_' + chunkIndex + '.json')
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});
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}
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when(chunkUrl.fetchJson(), function(chunk) {
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xysData._chunkDownloadsInProgress[chunkIndex] = false;
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var samples = xysData._samples;
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var newSamples = chunk.samples;
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var startIndex = chunkIndex * xysData._samplesPerXysFile * 3;
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for ( var i = 0, len = newSamples.length; i < len; ++i) {
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samples[startIndex + i] = newSamples[i];
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}
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deferred.resolve();
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});
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return deferred.promise;
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}
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return Iau2006XysData;
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});
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