forked from CesiumGS/cesium
-
Notifications
You must be signed in to change notification settings - Fork 0
/
EarthOrientationParameters.js
431 lines (386 loc) · 14.9 KB
/
EarthOrientationParameters.js
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
import binarySearch from "./binarySearch.js";
import defaultValue from "./defaultValue.js";
import defined from "./defined.js";
import EarthOrientationParametersSample from "./EarthOrientationParametersSample.js";
import JulianDate from "./JulianDate.js";
import LeapSecond from "./LeapSecond.js";
import Resource from "./Resource.js";
import RuntimeError from "./RuntimeError.js";
import TimeConstants from "./TimeConstants.js";
import TimeStandard from "./TimeStandard.js";
/**
* Specifies Earth polar motion coordinates and the difference between UT1 and UTC.
* These Earth Orientation Parameters (EOP) are primarily used in the transformation from
* the International Celestial Reference Frame (ICRF) to the International Terrestrial
* Reference Frame (ITRF).
*
* @alias EarthOrientationParameters
* @constructor
*
* @param {Object} [options] Object with the following properties:
* @param {Resource|String} [options.url] The URL from which to obtain EOP data. If neither this
* parameter nor options.data is specified, all EOP values are assumed
* to be 0.0. If options.data is specified, this parameter is
* ignored.
* @param {Object} [options.data] The actual EOP data. If neither this
* parameter nor options.data is specified, all EOP values are assumed
* to be 0.0.
* @param {Boolean} [options.addNewLeapSeconds=true] True if leap seconds that
* are specified in the EOP data but not in {@link JulianDate.leapSeconds}
* should be added to {@link JulianDate.leapSeconds}. False if
* new leap seconds should be handled correctly in the context
* of the EOP data but otherwise ignored.
*
* @example
* // An example EOP data file, EOP.json:
* {
* "columnNames" : ["dateIso8601","modifiedJulianDateUtc","xPoleWanderRadians","yPoleWanderRadians","ut1MinusUtcSeconds","lengthOfDayCorrectionSeconds","xCelestialPoleOffsetRadians","yCelestialPoleOffsetRadians","taiMinusUtcSeconds"],
* "samples" : [
* "2011-07-01T00:00:00Z",55743.0,2.117957047295119e-7,2.111518721609984e-6,-0.2908948,-2.956e-4,3.393695767766752e-11,3.3452143996557983e-10,34.0,
* "2011-07-02T00:00:00Z",55744.0,2.193297093339541e-7,2.115460256837405e-6,-0.29065,-1.824e-4,-8.241832578862112e-11,5.623838700870617e-10,34.0,
* "2011-07-03T00:00:00Z",55745.0,2.262286080161428e-7,2.1191157519929706e-6,-0.2905572,1.9e-6,-3.490658503988659e-10,6.981317007977318e-10,34.0
* ]
* }
*
* @example
* // Loading the EOP data
* const eop = new Cesium.EarthOrientationParameters({ url : 'Data/EOP.json' });
* Cesium.Transforms.earthOrientationParameters = eop;
*
* @private
*/
function EarthOrientationParameters(options) {
options = defaultValue(options, defaultValue.EMPTY_OBJECT);
this._dates = undefined;
this._samples = undefined;
this._dateColumn = -1;
this._xPoleWanderRadiansColumn = -1;
this._yPoleWanderRadiansColumn = -1;
this._ut1MinusUtcSecondsColumn = -1;
this._xCelestialPoleOffsetRadiansColumn = -1;
this._yCelestialPoleOffsetRadiansColumn = -1;
this._taiMinusUtcSecondsColumn = -1;
this._columnCount = 0;
this._lastIndex = -1;
this._downloadPromise = undefined;
this._dataError = undefined;
this._addNewLeapSeconds = defaultValue(options.addNewLeapSeconds, true);
if (defined(options.data)) {
// Use supplied EOP data.
onDataReady(this, options.data);
} else if (defined(options.url)) {
const resource = Resource.createIfNeeded(options.url);
// Download EOP data.
const that = this;
this._downloadPromise = resource
.fetchJson()
.then(function (eopData) {
onDataReady(that, eopData);
})
.catch(function () {
that._dataError = `An error occurred while retrieving the EOP data from the URL ${resource.url}.`;
});
} else {
// Use all zeros for EOP data.
onDataReady(this, {
columnNames: [
"dateIso8601",
"modifiedJulianDateUtc",
"xPoleWanderRadians",
"yPoleWanderRadians",
"ut1MinusUtcSeconds",
"lengthOfDayCorrectionSeconds",
"xCelestialPoleOffsetRadians",
"yCelestialPoleOffsetRadians",
"taiMinusUtcSeconds",
],
samples: [],
});
}
}
/**
* A default {@link EarthOrientationParameters} instance that returns zero for all EOP values.
*/
EarthOrientationParameters.NONE = Object.freeze({
getPromiseToLoad: function () {
return Promise.resolve();
},
compute: function (date, result) {
if (!defined(result)) {
result = new EarthOrientationParametersSample(0.0, 0.0, 0.0, 0.0, 0.0);
} else {
result.xPoleWander = 0.0;
result.yPoleWander = 0.0;
result.xPoleOffset = 0.0;
result.yPoleOffset = 0.0;
result.ut1MinusUtc = 0.0;
}
return result;
},
});
/**
* Gets a promise that, when resolved, indicates that the EOP data has been loaded and is
* ready to use.
*
* @returns {Promise<void>} The promise.
*/
EarthOrientationParameters.prototype.getPromiseToLoad = function () {
return Promise.resolve(this._downloadPromise);
};
/**
* Computes the Earth Orientation Parameters (EOP) for a given date by interpolating.
* If the EOP data has not yet been download, this method returns undefined.
*
* @param {JulianDate} date The date for each to evaluate the EOP.
* @param {EarthOrientationParametersSample} [result] The instance to which to copy the result.
* If this parameter is undefined, a new instance is created and returned.
* @returns {EarthOrientationParametersSample} The EOP evaluated at the given date, or
* undefined if the data necessary to evaluate EOP at the date has not yet been
* downloaded.
*
* @exception {RuntimeError} The loaded EOP data has an error and cannot be used.
*
* @see EarthOrientationParameters#getPromiseToLoad
*/
EarthOrientationParameters.prototype.compute = function (date, result) {
// We cannot compute until the samples are available.
if (!defined(this._samples)) {
if (defined(this._dataError)) {
throw new RuntimeError(this._dataError);
}
return undefined;
}
if (!defined(result)) {
result = new EarthOrientationParametersSample(0.0, 0.0, 0.0, 0.0, 0.0);
}
if (this._samples.length === 0) {
result.xPoleWander = 0.0;
result.yPoleWander = 0.0;
result.xPoleOffset = 0.0;
result.yPoleOffset = 0.0;
result.ut1MinusUtc = 0.0;
return result;
}
const dates = this._dates;
const lastIndex = this._lastIndex;
let before = 0;
let after = 0;
if (defined(lastIndex)) {
const previousIndexDate = dates[lastIndex];
const nextIndexDate = dates[lastIndex + 1];
const isAfterPrevious = JulianDate.lessThanOrEquals(
previousIndexDate,
date
);
const isAfterLastSample = !defined(nextIndexDate);
const isBeforeNext =
isAfterLastSample || JulianDate.greaterThanOrEquals(nextIndexDate, date);
if (isAfterPrevious && isBeforeNext) {
before = lastIndex;
if (!isAfterLastSample && nextIndexDate.equals(date)) {
++before;
}
after = before + 1;
interpolate(this, dates, this._samples, date, before, after, result);
return result;
}
}
let index = binarySearch(dates, date, JulianDate.compare, this._dateColumn);
if (index >= 0) {
// If the next entry is the same date, use the later entry. This way, if two entries
// describe the same moment, one before a leap second and the other after, then we will use
// the post-leap second data.
if (index < dates.length - 1 && dates[index + 1].equals(date)) {
++index;
}
before = index;
after = index;
} else {
after = ~index;
before = after - 1;
// Use the first entry if the date requested is before the beginning of the data.
if (before < 0) {
before = 0;
}
}
this._lastIndex = before;
interpolate(this, dates, this._samples, date, before, after, result);
return result;
};
function compareLeapSecondDates(leapSecond, dateToFind) {
return JulianDate.compare(leapSecond.julianDate, dateToFind);
}
function onDataReady(eop, eopData) {
if (!defined(eopData.columnNames)) {
eop._dataError =
"Error in loaded EOP data: The columnNames property is required.";
return;
}
if (!defined(eopData.samples)) {
eop._dataError =
"Error in loaded EOP data: The samples property is required.";
return;
}
const dateColumn = eopData.columnNames.indexOf("modifiedJulianDateUtc");
const xPoleWanderRadiansColumn = eopData.columnNames.indexOf(
"xPoleWanderRadians"
);
const yPoleWanderRadiansColumn = eopData.columnNames.indexOf(
"yPoleWanderRadians"
);
const ut1MinusUtcSecondsColumn = eopData.columnNames.indexOf(
"ut1MinusUtcSeconds"
);
const xCelestialPoleOffsetRadiansColumn = eopData.columnNames.indexOf(
"xCelestialPoleOffsetRadians"
);
const yCelestialPoleOffsetRadiansColumn = eopData.columnNames.indexOf(
"yCelestialPoleOffsetRadians"
);
const taiMinusUtcSecondsColumn = eopData.columnNames.indexOf(
"taiMinusUtcSeconds"
);
if (
dateColumn < 0 ||
xPoleWanderRadiansColumn < 0 ||
yPoleWanderRadiansColumn < 0 ||
ut1MinusUtcSecondsColumn < 0 ||
xCelestialPoleOffsetRadiansColumn < 0 ||
yCelestialPoleOffsetRadiansColumn < 0 ||
taiMinusUtcSecondsColumn < 0
) {
eop._dataError =
"Error in loaded EOP data: The columnNames property must include modifiedJulianDateUtc, xPoleWanderRadians, yPoleWanderRadians, ut1MinusUtcSeconds, xCelestialPoleOffsetRadians, yCelestialPoleOffsetRadians, and taiMinusUtcSeconds columns";
return;
}
const samples = (eop._samples = eopData.samples);
const dates = (eop._dates = []);
eop._dateColumn = dateColumn;
eop._xPoleWanderRadiansColumn = xPoleWanderRadiansColumn;
eop._yPoleWanderRadiansColumn = yPoleWanderRadiansColumn;
eop._ut1MinusUtcSecondsColumn = ut1MinusUtcSecondsColumn;
eop._xCelestialPoleOffsetRadiansColumn = xCelestialPoleOffsetRadiansColumn;
eop._yCelestialPoleOffsetRadiansColumn = yCelestialPoleOffsetRadiansColumn;
eop._taiMinusUtcSecondsColumn = taiMinusUtcSecondsColumn;
eop._columnCount = eopData.columnNames.length;
eop._lastIndex = undefined;
let lastTaiMinusUtc;
const addNewLeapSeconds = eop._addNewLeapSeconds;
// Convert the ISO8601 dates to JulianDates.
for (let i = 0, len = samples.length; i < len; i += eop._columnCount) {
const mjd = samples[i + dateColumn];
const taiMinusUtc = samples[i + taiMinusUtcSecondsColumn];
const day = mjd + TimeConstants.MODIFIED_JULIAN_DATE_DIFFERENCE;
const date = new JulianDate(day, taiMinusUtc, TimeStandard.TAI);
dates.push(date);
if (addNewLeapSeconds) {
if (taiMinusUtc !== lastTaiMinusUtc && defined(lastTaiMinusUtc)) {
// We crossed a leap second boundary, so add the leap second
// if it does not already exist.
const leapSeconds = JulianDate.leapSeconds;
const leapSecondIndex = binarySearch(
leapSeconds,
date,
compareLeapSecondDates
);
if (leapSecondIndex < 0) {
const leapSecond = new LeapSecond(date, taiMinusUtc);
leapSeconds.splice(~leapSecondIndex, 0, leapSecond);
}
}
lastTaiMinusUtc = taiMinusUtc;
}
}
}
function fillResultFromIndex(eop, samples, index, columnCount, result) {
const start = index * columnCount;
result.xPoleWander = samples[start + eop._xPoleWanderRadiansColumn];
result.yPoleWander = samples[start + eop._yPoleWanderRadiansColumn];
result.xPoleOffset = samples[start + eop._xCelestialPoleOffsetRadiansColumn];
result.yPoleOffset = samples[start + eop._yCelestialPoleOffsetRadiansColumn];
result.ut1MinusUtc = samples[start + eop._ut1MinusUtcSecondsColumn];
}
function linearInterp(dx, y1, y2) {
return y1 + dx * (y2 - y1);
}
function interpolate(eop, dates, samples, date, before, after, result) {
const columnCount = eop._columnCount;
// First check the bounds on the EOP data
// If we are after the bounds of the data, return zeros.
// The 'before' index should never be less than zero.
if (after > dates.length - 1) {
result.xPoleWander = 0;
result.yPoleWander = 0;
result.xPoleOffset = 0;
result.yPoleOffset = 0;
result.ut1MinusUtc = 0;
return result;
}
const beforeDate = dates[before];
const afterDate = dates[after];
if (beforeDate.equals(afterDate) || date.equals(beforeDate)) {
fillResultFromIndex(eop, samples, before, columnCount, result);
return result;
} else if (date.equals(afterDate)) {
fillResultFromIndex(eop, samples, after, columnCount, result);
return result;
}
const factor =
JulianDate.secondsDifference(date, beforeDate) /
JulianDate.secondsDifference(afterDate, beforeDate);
const startBefore = before * columnCount;
const startAfter = after * columnCount;
// Handle UT1 leap second edge case
let beforeUt1MinusUtc = samples[startBefore + eop._ut1MinusUtcSecondsColumn];
let afterUt1MinusUtc = samples[startAfter + eop._ut1MinusUtcSecondsColumn];
const offsetDifference = afterUt1MinusUtc - beforeUt1MinusUtc;
if (offsetDifference > 0.5 || offsetDifference < -0.5) {
// The absolute difference between the values is more than 0.5, so we may have
// crossed a leap second. Check if this is the case and, if so, adjust the
// afterValue to account for the leap second. This way, our interpolation will
// produce reasonable results.
const beforeTaiMinusUtc =
samples[startBefore + eop._taiMinusUtcSecondsColumn];
const afterTaiMinusUtc =
samples[startAfter + eop._taiMinusUtcSecondsColumn];
if (beforeTaiMinusUtc !== afterTaiMinusUtc) {
if (afterDate.equals(date)) {
// If we are at the end of the leap second interval, take the second value
// Otherwise, the interpolation below will yield the wrong side of the
// discontinuity
// At the end of the leap second, we need to start accounting for the jump
beforeUt1MinusUtc = afterUt1MinusUtc;
} else {
// Otherwise, remove the leap second so that the interpolation is correct
afterUt1MinusUtc -= afterTaiMinusUtc - beforeTaiMinusUtc;
}
}
}
result.xPoleWander = linearInterp(
factor,
samples[startBefore + eop._xPoleWanderRadiansColumn],
samples[startAfter + eop._xPoleWanderRadiansColumn]
);
result.yPoleWander = linearInterp(
factor,
samples[startBefore + eop._yPoleWanderRadiansColumn],
samples[startAfter + eop._yPoleWanderRadiansColumn]
);
result.xPoleOffset = linearInterp(
factor,
samples[startBefore + eop._xCelestialPoleOffsetRadiansColumn],
samples[startAfter + eop._xCelestialPoleOffsetRadiansColumn]
);
result.yPoleOffset = linearInterp(
factor,
samples[startBefore + eop._yCelestialPoleOffsetRadiansColumn],
samples[startAfter + eop._yCelestialPoleOffsetRadiansColumn]
);
result.ut1MinusUtc = linearInterp(
factor,
beforeUt1MinusUtc,
afterUt1MinusUtc
);
return result;
}
export default EarthOrientationParameters;