1 /* Copyright 2002-2013 CS Systèmes d'Information
2 * Licensed to CS Systèmes d'Information (CS) under one or more
3 * contributor license agreements. See the NOTICE file distributed with
4 * this work for additional information regarding copyright ownership.
5 * CS licenses this file to You under the Apache License, Version 2.0
6 * (the "License"); you may not use this file except in compliance with
7 * the License. You may obtain a copy of the License at
8 *
9 * http://www.apache.org/licenses/LICENSE-2.0
10 *
11 * Unless required by applicable law or agreed to in writing, software
12 * distributed under the License is distributed on an "AS IS" BASIS,
13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14 * See the License for the specific language governing permissions and
15 * limitations under the License.
16 */
17 package org.orekit.time;
18
19 import java.io.Serializable;
20 import java.util.Date;
21
22 import org.apache.commons.math3.util.FastMath;
23 import org.apache.commons.math3.util.MathArrays;
24 import org.orekit.errors.OrekitException;
25 import org.orekit.errors.OrekitMessages;
26 import org.orekit.utils.Constants;
27
28
29 /** This class represents a specific instant in time.
30
31 * <p>Instances of this class are considered to be absolute in the sense
32 * that each one represent the occurrence of some event and can be compared
33 * to other instances or located in <em>any</em> {@link TimeScale time scale}. In
34 * other words the different locations of an event with respect to two different
35 * time scales (say {@link TAIScale TAI} and {@link UTCScale UTC} for example) are
36 * simply different perspective related to a single object. Only one
37 * <code>AbsoluteDate</code> instance is needed, both representations being available
38 * from this single instance by specifying the time scales as parameter when calling
39 * the ad-hoc methods.</p>
40 *
41 * <p>Since an instance is not bound to a specific time-scale, all methods related
42 * to the location of the date within some time scale require to provide the time
43 * scale as an argument. It is therefore possible to define a date in one time scale
44 * and to use it in another one. An example of such use is to read a date from a file
45 * in UTC and write it in another file in TAI. This can be done as follows:</p>
46 * <pre>
47 * DateTimeComponents utcComponents = readNextDate();
48 * AbsoluteDate date = new AbsoluteDate(utcComponents, TimeScalesFactory.getUTC());
49 * writeNextDate(date.getComponents(TimeScalesFactory.getTAI()));
50 * </pre>
51 *
52 * <p>Two complementary views are available:</p>
53 * <ul>
54 * <li><p>location view (mainly for input/output or conversions)</p>
55 * <p>locations represent the coordinate of one event with respect to a
56 * {@link TimeScale time scale}. The related methods are {@link
57 * #AbsoluteDate(DateComponents, TimeComponents, TimeScale)}, {@link
58 * #AbsoluteDate(int, int, int, int, int, double, TimeScale)}, {@link
59 * #AbsoluteDate(int, int, int, TimeScale)}, {@link #AbsoluteDate(Date,
60 * TimeScale)}, {@link #createGPSDate(int, double)}, {@link
61 * #parseCCSDSCalendarSegmentedTimeCode(byte, byte[])}, toString(){@link
62 * #toDate(TimeScale)}, {@link #toString(TimeScale) toString(timeScale)},
63 * {@link #toString()}, and {@link #timeScalesOffset}.</p>
64 * </li>
65 * <li><p>offset view (mainly for physical computation)</p>
66 * <p>offsets represent either the flow of time between two events
67 * (two instances of the class) or durations. They are counted in seconds,
68 * are continuous and could be measured using only a virtually perfect stopwatch.
69 * The related methods are {@link #AbsoluteDate(AbsoluteDate, double)},
70 * {@link #parseCCSDSUnsegmentedTimeCode(byte, byte, byte[], AbsoluteDate)},
71 * {@link #parseCCSDSDaySegmentedTimeCode(byte, byte[], DateComponents)},
72 * {@link #durationFrom(AbsoluteDate)}, {@link #compareTo(AbsoluteDate)}, {@link #equals(Object)}
73 * and {@link #hashCode()}.</p>
74 * </li>
75 * </ul>
76 * <p>
77 * A few reference epochs which are commonly used in space systems have been defined. These
78 * epochs can be used as the basis for offset computation. The supported epochs are:
79 * {@link #JULIAN_EPOCH}, {@link #MODIFIED_JULIAN_EPOCH}, {@link #FIFTIES_EPOCH},
80 * {@link #CCSDS_EPOCH}, {@link #GALILEO_EPOCH}, {@link #GPS_EPOCH}, {@link #J2000_EPOCH},
81 * {@link #JAVA_EPOCH}. There are also two factory methods {@link #createJulianEpoch(double)}
82 * and {@link #createBesselianEpoch(double)} that can be used to compute other reference
83 * epochs like J1900.0 or B1950.0.
84 * In addition to these reference epochs, two other constants are defined for convenience:
85 * {@link #PAST_INFINITY} and {@link #FUTURE_INFINITY}, which can be used either as dummy
86 * dates when a date is not yet initialized, or for initialization of loops searching for
87 * a min or max date.
88 * </p>
89 * <p>
90 * Instances of the <code>AbsoluteDate</code> class are guaranteed to be immutable.
91 * </p>
92 * @author Luc Maisonobe
93 * @see TimeScale
94 * @see TimeStamped
95 * @see ChronologicalComparator
96 */
97 public class AbsoluteDate
98 implements TimeStamped, TimeShiftable<AbsoluteDate>, Comparable<AbsoluteDate>, Serializable {
99
100 /** Reference epoch for julian dates: -4712-01-01T12:00:00 Terrestrial Time.
101 * <p>Both <code>java.util.Date</code> and {@link DateComponents} classes
102 * follow the astronomical conventions and consider a year 0 between
103 * years -1 and +1, hence this reference date lies in year -4712 and not
104 * in year -4713 as can be seen in other documents or programs that obey
105 * a different convention (for example the <code>convcal</code> utility).</p>
106 */
107 public static final AbsoluteDate JULIAN_EPOCH =
108 new AbsoluteDate(DateComponents.JULIAN_EPOCH, TimeComponents.H12, TimeScalesFactory.getTT());
109
110 /** Reference epoch for modified julian dates: 1858-11-17T00:00:00 Terrestrial Time. */
111 public static final AbsoluteDate MODIFIED_JULIAN_EPOCH =
112 new AbsoluteDate(DateComponents.MODIFIED_JULIAN_EPOCH, TimeComponents.H00, TimeScalesFactory.getTT());
113
114 /** Reference epoch for 1950 dates: 1950-01-01T00:00:00 Terrestrial Time. */
115 public static final AbsoluteDate FIFTIES_EPOCH =
116 new AbsoluteDate(DateComponents.FIFTIES_EPOCH, TimeComponents.H00, TimeScalesFactory.getTT());
117
118 /** Reference epoch for CCSDS Time Code Format (CCSDS 301.0-B-4):
119 * 1958-01-01T00:00:00 International Atomic Time (<em>not</em> UTC). */
120 public static final AbsoluteDate CCSDS_EPOCH =
121 new AbsoluteDate(DateComponents.CCSDS_EPOCH, TimeComponents.H00, TimeScalesFactory.getTAI());
122
123 /** Reference epoch for Galileo System Time: 1999-08-22T00:00:00 UTC. */
124 public static final AbsoluteDate GALILEO_EPOCH =
125 new AbsoluteDate(DateComponents.GALILEO_EPOCH, new TimeComponents(0, 0, 32),
126 TimeScalesFactory.getTAI());
127
128 /** Reference epoch for GPS weeks: 1980-01-06T00:00:00 GPS time. */
129 public static final AbsoluteDate GPS_EPOCH =
130 new AbsoluteDate(DateComponents.GPS_EPOCH, TimeComponents.H00, TimeScalesFactory.getGPS());
131
132 /** J2000.0 Reference epoch: 2000-01-01T12:00:00 Terrestrial Time (<em>not</em> UTC).
133 * @see #createJulianEpoch(double)
134 * @see #createBesselianEpoch(double)
135 */
136 public static final AbsoluteDate J2000_EPOCH =
137 new AbsoluteDate(DateComponents.J2000_EPOCH, TimeComponents.H12, TimeScalesFactory.getTT());
138
139 /** Java Reference epoch: 1970-01-01T00:00:00 Universal Time Coordinate.
140 * <p>
141 * Between 1968-02-01 and 1972-01-01, UTC-TAI = 4.213 170 0s + (MJD - 39 126) x 0.002 592s.
142 * As on 1970-01-01 MJD = 40587, UTC-TAI = 8.000082s
143 * </p>
144 */
145 public static final AbsoluteDate JAVA_EPOCH =
146 new AbsoluteDate(DateComponents.JAVA_EPOCH, TimeScalesFactory.getTAI()).shiftedBy(8.000082);
147
148 /** Dummy date at infinity in the past direction. */
149 public static final AbsoluteDate PAST_INFINITY = JAVA_EPOCH.shiftedBy(Double.NEGATIVE_INFINITY);
150
151 /** Dummy date at infinity in the future direction. */
152 public static final AbsoluteDate FUTURE_INFINITY = JAVA_EPOCH.shiftedBy(Double.POSITIVE_INFINITY);
153
154 /** Serializable UID. */
155 private static final long serialVersionUID = 617061803741806846L;
156
157 /** Reference epoch in seconds from 2000-01-01T12:00:00 TAI.
158 * <p>Beware, it is not {@link #J2000_EPOCH} since it is in TAI and not in TT.</p> */
159 private final long epoch;
160
161 /** Offset from the reference epoch in seconds. */
162 private final double offset;
163
164 /** Create an instance with a default value ({@link #J2000_EPOCH}).
165 */
166 public AbsoluteDate() {
167 epoch = J2000_EPOCH.epoch;
168 offset = J2000_EPOCH.offset;
169 }
170
171 /** Build an instance from a location (parsed from a string) in a {@link TimeScale time scale}.
172 * <p>
173 * The supported formats for location are mainly the ones defined in ISO-8601 standard,
174 * the exact subset is explained in {@link DateTimeComponents#parseDateTime(String)},
175 * {@link DateComponents#parseDate(String)} and {@link TimeComponents#parseTime(String)}.
176 * </p>
177 * <p>
178 * As CCSDS ASCII calendar segmented time code is a trimmed down version of ISO-8601,
179 * it is also supported by this constructor.
180 * </p>
181 * @param location location in the time scale, must be in a supported format
182 * @param timeScale time scale
183 * @exception IllegalArgumentException if location string is not in a supported format
184 */
185 public AbsoluteDate(final String location, final TimeScale timeScale) {
186 this(DateTimeComponents.parseDateTime(location), timeScale);
187 }
188
189 /** Build an instance from a location in a {@link TimeScale time scale}.
190 * @param location location in the time scale
191 * @param timeScale time scale
192 */
193 public AbsoluteDate(final DateTimeComponents location, final TimeScale timeScale) {
194 this(location.getDate(), location.getTime(), timeScale);
195 }
196
197 /** Build an instance from a location in a {@link TimeScale time scale}.
198 * @param date date location in the time scale
199 * @param time time location in the time scale
200 * @param timeScale time scale
201 */
202 public AbsoluteDate(final DateComponents date, final TimeComponents time,
203 final TimeScale timeScale) {
204
205 final double seconds = time.getSecond();
206 final double tsOffset = timeScale.offsetToTAI(date, time);
207
208 // compute sum exactly, using Møller-Knuth TwoSum algorithm without branching
209 // the following statements must NOT be simplified, they rely on floating point
210 // arithmetic properties (rounding and representable numbers)
211 // at the end, the EXACT result of addition seconds + tsOffset
212 // is sum + residual, where sum is the closest representable number to the exact
213 // result and residual is the missing part that does not fit in the first number
214 final double sum = seconds + tsOffset;
215 final double sPrime = sum - tsOffset;
216 final double tPrime = sum - sPrime;
217 final double deltaS = seconds - sPrime;
218 final double deltaT = tsOffset - tPrime;
219 final double residual = deltaS + deltaT;
220 final long dl = (long) FastMath.floor(sum);
221
222 offset = (sum - dl) + residual;
223 epoch = 60l * ((date.getJ2000Day() * 24l + time.getHour()) * 60l + time.getMinute() - 720l) + dl;
224
225 }
226
227 /** Build an instance from a location in a {@link TimeScale time scale}.
228 * @param year year number (may be 0 or negative for BC years)
229 * @param month month number from 1 to 12
230 * @param day day number from 1 to 31
231 * @param hour hour number from 0 to 23
232 * @param minute minute number from 0 to 59
233 * @param second second number from 0.0 to 60.0 (excluded)
234 * @param timeScale time scale
235 * @exception IllegalArgumentException if inconsistent arguments
236 * are given (parameters out of range)
237 */
238 public AbsoluteDate(final int year, final int month, final int day,
239 final int hour, final int minute, final double second,
240 final TimeScale timeScale) throws IllegalArgumentException {
241 this(new DateComponents(year, month, day), new TimeComponents(hour, minute, second), timeScale);
242 }
243
244 /** Build an instance from a location in a {@link TimeScale time scale}.
245 * @param year year number (may be 0 or negative for BC years)
246 * @param month month enumerate
247 * @param day day number from 1 to 31
248 * @param hour hour number from 0 to 23
249 * @param minute minute number from 0 to 59
250 * @param second second number from 0.0 to 60.0 (excluded)
251 * @param timeScale time scale
252 * @exception IllegalArgumentException if inconsistent arguments
253 * are given (parameters out of range)
254 */
255 public AbsoluteDate(final int year, final Month month, final int day,
256 final int hour, final int minute, final double second,
257 final TimeScale timeScale) throws IllegalArgumentException {
258 this(new DateComponents(year, month, day), new TimeComponents(hour, minute, second), timeScale);
259 }
260
261 /** Build an instance from a location in a {@link TimeScale time scale}.
262 * <p>The hour is set to 00:00:00.000.</p>
263 * @param date date location in the time scale
264 * @param timeScale time scale
265 * @exception IllegalArgumentException if inconsistent arguments
266 * are given (parameters out of range)
267 */
268 public AbsoluteDate(final DateComponents date, final TimeScale timeScale)
269 throws IllegalArgumentException {
270 this(date, TimeComponents.H00, timeScale);
271 }
272
273 /** Build an instance from a location in a {@link TimeScale time scale}.
274 * <p>The hour is set to 00:00:00.000.</p>
275 * @param year year number (may be 0 or negative for BC years)
276 * @param month month number from 1 to 12
277 * @param day day number from 1 to 31
278 * @param timeScale time scale
279 * @exception IllegalArgumentException if inconsistent arguments
280 * are given (parameters out of range)
281 */
282 public AbsoluteDate(final int year, final int month, final int day,
283 final TimeScale timeScale) throws IllegalArgumentException {
284 this(new DateComponents(year, month, day), TimeComponents.H00, timeScale);
285 }
286
287 /** Build an instance from a location in a {@link TimeScale time scale}.
288 * <p>The hour is set to 00:00:00.000.</p>
289 * @param year year number (may be 0 or negative for BC years)
290 * @param month month enumerate
291 * @param day day number from 1 to 31
292 * @param timeScale time scale
293 * @exception IllegalArgumentException if inconsistent arguments
294 * are given (parameters out of range)
295 */
296 public AbsoluteDate(final int year, final Month month, final int day,
297 final TimeScale timeScale) throws IllegalArgumentException {
298 this(new DateComponents(year, month, day), TimeComponents.H00, timeScale);
299 }
300
301 /** Build an instance from a location in a {@link TimeScale time scale}.
302 * @param location location in the time scale
303 * @param timeScale time scale
304 */
305 public AbsoluteDate(final Date location, final TimeScale timeScale) {
306 this(new DateComponents(DateComponents.JAVA_EPOCH,
307 (int) (location.getTime() / 86400000l)),
308 new TimeComponents(0.001 * (location.getTime() % 86400000l)),
309 timeScale);
310 }
311
312 /** Build an instance from an elapsed duration since to another instant.
313 * <p>It is important to note that the elapsed duration is <em>not</em>
314 * the difference between two readings on a time scale. As an example,
315 * the duration between the two instants leading to the readings
316 * 2005-12-31T23:59:59 and 2006-01-01T00:00:00 in the {@link UTCScale UTC}
317 * time scale is <em>not</em> 1 second, but a stop watch would have measured
318 * an elapsed duration of 2 seconds between these two instances because a leap
319 * second was introduced at the end of 2005 in this time scale.</p>
320 * <p>This constructor is the reverse of the {@link #durationFrom(AbsoluteDate)}
321 * method.</p>
322 * @param since start instant of the measured duration
323 * @param elapsedDuration physically elapsed duration from the <code>since</code>
324 * instant, as measured in a regular time scale
325 * @see #durationFrom(AbsoluteDate)
326 */
327 public AbsoluteDate(final AbsoluteDate since, final double elapsedDuration) {
328
329 final double sum = since.offset + elapsedDuration;
330 if (Double.isInfinite(sum)) {
331 offset = sum;
332 epoch = (sum < 0) ? Long.MIN_VALUE : Long.MAX_VALUE;
333 } else {
334 // compute sum exactly, using Møller-Knuth TwoSum algorithm without branching
335 // the following statements must NOT be simplified, they rely on floating point
336 // arithmetic properties (rounding and representable numbers)
337 // at the end, the EXACT result of addition since.offset + elapsedDuration
338 // is sum + residual, where sum is the closest representable number to the exact
339 // result and residual is the missing part that does not fit in the first number
340 final double oPrime = sum - elapsedDuration;
341 final double dPrime = sum - oPrime;
342 final double deltaO = since.offset - oPrime;
343 final double deltaD = elapsedDuration - dPrime;
344 final double residual = deltaO + deltaD;
345 final long dl = (long) FastMath.floor(sum);
346 offset = (sum - dl) + residual;
347 epoch = since.epoch + dl;
348 }
349 }
350
351 /** Build an instance from an apparent clock offset with respect to another
352 * instant <em>in the perspective of a specific {@link TimeScale time scale}</em>.
353 * <p>It is important to note that the apparent clock offset <em>is</em> the
354 * difference between two readings on a time scale and <em>not</em> an elapsed
355 * duration. As an example, the apparent clock offset between the two instants
356 * leading to the readings 2005-12-31T23:59:59 and 2006-01-01T00:00:00 in the
357 * {@link UTCScale UTC} time scale is 1 second, but the elapsed duration is 2
358 * seconds because a leap second has been introduced at the end of 2005 in this
359 * time scale.</p>
360 * <p>This constructor is the reverse of the {@link #offsetFrom(AbsoluteDate,
361 * TimeScale)} method.</p>
362 * @param reference reference instant
363 * @param apparentOffset apparent clock offset from the reference instant
364 * (difference between two readings in the specified time scale)
365 * @param timeScale time scale with respect to which the offset is defined
366 * @see #offsetFrom(AbsoluteDate, TimeScale)
367 */
368 public AbsoluteDate(final AbsoluteDate reference, final double apparentOffset,
369 final TimeScale timeScale) {
370 this(new DateTimeComponents(reference.getComponents(timeScale), apparentOffset),
371 timeScale);
372 }
373
374 /** Build an instance from a CCSDS Unsegmented Time Code (CUC).
375 * <p>
376 * CCSDS Unsegmented Time Code is defined in the blue book:
377 * CCSDS Time Code Format (CCSDS 301.0-B-4) published in November 2010
378 * </p>
379 * <p>
380 * If the date to be parsed is formatted using version 3 of the standard
381 * (CCSDS 301.0-B-3 published in 2002) or if the extension of the preamble
382 * field introduced in version 4 of the standard is not used, then the
383 * {@code preambleField2} parameter can be set to 0.
384 * </p>
385 * @param preambleField1 first byte of the field specifying the format, often
386 * not transmitted in data interfaces, as it is constant for a given data interface
387 * @param preambleField2 second byte of the field specifying the format
388 * (added in revision 4 of the CCSDS standard in 2010), often not transmitted in data
389 * interfaces, as it is constant for a given data interface (value ignored if presence
390 * not signaled in {@code preambleField1})
391 * @param timeField byte array containing the time code
392 * @param agencyDefinedEpoch reference epoch, ignored if the preamble field
393 * specifies the {@link #CCSDS_EPOCH CCSDS reference epoch} is used (and hence
394 * may be null in this case)
395 * @return an instance corresponding to the specified date
396 * @throws OrekitException if preamble is inconsistent with Unsegmented Time Code,
397 * or if it is inconsistent with time field, or if agency epoch is needed but not provided
398 */
399 public static AbsoluteDate parseCCSDSUnsegmentedTimeCode(final byte preambleField1,
400 final byte preambleField2,
401 final byte[] timeField,
402 final AbsoluteDate agencyDefinedEpoch)
403 throws OrekitException {
404
405 // time code identification and reference epoch
406 final AbsoluteDate epoch;
407 switch (preambleField1 & 0x70) {
408 case 0x10:
409 // the reference epoch is CCSDS epoch 1958-01-01T00:00:00 TAI
410 epoch = CCSDS_EPOCH;
411 break;
412 case 0x20:
413 // the reference epoch is agency defined
414 if (agencyDefinedEpoch == null) {
415 throw new OrekitException(OrekitMessages.CCSDS_DATE_MISSING_AGENCY_EPOCH);
416 }
417 epoch = agencyDefinedEpoch;
418 break;
419 default :
420 throw new OrekitException(OrekitMessages.CCSDS_DATE_INVALID_PREAMBLE_FIELD,
421 formatByte(preambleField1));
422 }
423
424 // time field lengths
425 int coarseTimeLength = 1 + ((preambleField1 & 0x0C) >>> 2);
426 int fineTimeLength = preambleField1 & 0x03;
427
428 if ((preambleField1 & 0x80) != 0x0) {
429 // there is an additional octet in preamble field
430 coarseTimeLength += (preambleField2 & 0x60) >>> 5;
431 fineTimeLength += (preambleField2 & 0x1C) >>> 2;
432 }
433
434 if (timeField.length != coarseTimeLength + fineTimeLength) {
435 throw new OrekitException(OrekitMessages.CCSDS_DATE_INVALID_LENGTH_TIME_FIELD,
436 timeField.length, coarseTimeLength + fineTimeLength);
437 }
438
439 double seconds = 0;
440 for (int i = 0; i < coarseTimeLength; ++i) {
441 seconds = seconds * 256 + toUnsigned(timeField[i]);
442 }
443 double subseconds = 0;
444 for (int i = timeField.length - 1; i >= coarseTimeLength; --i) {
445 subseconds = (subseconds + toUnsigned(timeField[i])) / 256;
446 }
447
448 return new AbsoluteDate(epoch, seconds).shiftedBy(subseconds);
449
450 }
451
452 /** Build an instance from a CCSDS Day Segmented Time Code (CDS).
453 * <p>
454 * CCSDS Day Segmented Time Code is defined in the blue book:
455 * CCSDS Time Code Format (CCSDS 301.0-B-4) published in November 2010
456 * </p>
457 * @param preambleField field specifying the format, often not transmitted in
458 * data interfaces, as it is constant for a given data interface
459 * @param timeField byte array containing the time code
460 * @param agencyDefinedEpoch reference epoch, ignored if the preamble field
461 * specifies the {@link #CCSDS_EPOCH CCSDS reference epoch} is used (and hence
462 * may be null in this case)
463 * @return an instance corresponding to the specified date
464 * @throws OrekitException if preamble is inconsistent with Day Segmented Time Code,
465 * or if it is inconsistent with time field, or if agency epoch is needed but not provided,
466 * or it UTC time scale cannot be retrieved
467 */
468 public static AbsoluteDate parseCCSDSDaySegmentedTimeCode(final byte preambleField, final byte[] timeField,
469 final DateComponents agencyDefinedEpoch)
470 throws OrekitException {
471
472 // time code identification
473 if ((preambleField & 0xF0) != 0x40) {
474 throw new OrekitException(OrekitMessages.CCSDS_DATE_INVALID_PREAMBLE_FIELD,
475 formatByte(preambleField));
476 }
477
478 // reference epoch
479 final DateComponents epoch;
480 if ((preambleField & 0x08) == 0x00) {
481 // the reference epoch is CCSDS epoch 1958-01-01T00:00:00 TAI
482 epoch = DateComponents.CCSDS_EPOCH;
483 } else {
484 // the reference epoch is agency defined
485 if (agencyDefinedEpoch == null) {
486 throw new OrekitException(OrekitMessages.CCSDS_DATE_MISSING_AGENCY_EPOCH);
487 }
488 epoch = agencyDefinedEpoch;
489 }
490
491 // time field lengths
492 final int daySegmentLength = ((preambleField & 0x04) == 0x0) ? 2 : 3;
493 final int subMillisecondLength = (preambleField & 0x03) << 1;
494 if (subMillisecondLength == 6) {
495 throw new OrekitException(OrekitMessages.CCSDS_DATE_INVALID_PREAMBLE_FIELD,
496 formatByte(preambleField));
497 }
498 if (timeField.length != daySegmentLength + 4 + subMillisecondLength) {
499 throw new OrekitException(OrekitMessages.CCSDS_DATE_INVALID_LENGTH_TIME_FIELD,
500 timeField.length, daySegmentLength + 4 + subMillisecondLength);
501 }
502
503
504 int i = 0;
505 int day = 0;
506 while (i < daySegmentLength) {
507 day = day * 256 + toUnsigned(timeField[i++]);
508 }
509
510 long milliInDay = 0l;
511 while (i < daySegmentLength + 4) {
512 milliInDay = milliInDay * 256 + toUnsigned(timeField[i++]);
513 }
514 final int milli = (int) (milliInDay % 1000l);
515 final int seconds = (int) ((milliInDay - milli) / 1000l);
516
517 double subMilli = 0;
518 double divisor = 1;
519 while (i < timeField.length) {
520 subMilli = subMilli * 256 + toUnsigned(timeField[i++]);
521 divisor *= 1000;
522 }
523
524 final DateComponents date = new DateComponents(epoch, day);
525 final TimeComponents time = new TimeComponents(seconds);
526 return new AbsoluteDate(date, time, TimeScalesFactory.getUTC()).shiftedBy(milli * 1.0e-3 + subMilli / divisor);
527
528 }
529
530 /** Build an instance from a CCSDS Calendar Segmented Time Code (CCS).
531 * <p>
532 * CCSDS Calendar Segmented Time Code is defined in the blue book:
533 * CCSDS Time Code Format (CCSDS 301.0-B-4) published in November 2010
534 * </p>
535 * @param preambleField field specifying the format, often not transmitted in
536 * data interfaces, as it is constant for a given data interface
537 * @param timeField byte array containing the time code
538 * @return an instance corresponding to the specified date
539 * @throws OrekitException if preamble is inconsistent with Calendar Segmented Time Code,
540 * or if it is inconsistent with time field, or it UTC time scale cannot be retrieved
541 */
542 public static AbsoluteDate parseCCSDSCalendarSegmentedTimeCode(final byte preambleField, final byte[] timeField)
543 throws OrekitException {
544
545 // time code identification
546 if ((preambleField & 0xF0) != 0x50) {
547 throw new OrekitException(OrekitMessages.CCSDS_DATE_INVALID_PREAMBLE_FIELD,
548 formatByte(preambleField));
549 }
550
551 // time field length
552 final int length = 7 + (preambleField & 0x07);
553 if (length == 14) {
554 throw new OrekitException(OrekitMessages.CCSDS_DATE_INVALID_PREAMBLE_FIELD,
555 formatByte(preambleField));
556 }
557 if (timeField.length != length) {
558 throw new OrekitException(OrekitMessages.CCSDS_DATE_INVALID_LENGTH_TIME_FIELD,
559 timeField.length, length);
560 }
561
562 // date part in the first four bytes
563 final DateComponents date;
564 if ((preambleField & 0x08) == 0x00) {
565 // month of year and day of month variation
566 date = new DateComponents(toUnsigned(timeField[0]) * 256 + toUnsigned(timeField[1]),
567 toUnsigned(timeField[2]),
568 toUnsigned(timeField[3]));
569 } else {
570 // day of year variation
571 date = new DateComponents(toUnsigned(timeField[0]) * 256 + toUnsigned(timeField[1]),
572 toUnsigned(timeField[2]) * 256 + toUnsigned(timeField[3]));
573 }
574
575 // time part from bytes 5 to last (between 7 and 13 depending on precision)
576 final TimeComponents time = new TimeComponents(toUnsigned(timeField[4]),
577 toUnsigned(timeField[5]),
578 toUnsigned(timeField[6]));
579 double subSecond = 0;
580 double divisor = 1;
581 for (int i = 7; i < length; ++i) {
582 subSecond = subSecond * 100 + toUnsigned(timeField[i]);
583 divisor *= 100;
584 }
585
586 return new AbsoluteDate(date, time, TimeScalesFactory.getUTC()).shiftedBy(subSecond / divisor);
587
588 }
589
590 /** Decode a signed byte as an unsigned int value.
591 * @param b byte to decode
592 * @return an unsigned int value
593 */
594 private static int toUnsigned(final byte b) {
595 final int i = (int) b;
596 return (i < 0) ? 256 + i : i;
597 }
598
599 /** Format a byte as an hex string for error messages.
600 * @param data byte to format
601 * @return a formatted string
602 */
603 private static String formatByte(final byte data) {
604 return "0x" + Integer.toHexString(data).toUpperCase();
605 }
606
607 /** Build an instance corresponding to a GPS date.
608 * <p>GPS dates are provided as a week number starting at
609 * {@link #GPS_EPOCH GPS epoch} and as a number of milliseconds
610 * since week start.</p>
611 * @param weekNumber week number since {@link #GPS_EPOCH GPS epoch}
612 * @param milliInWeek number of milliseconds since week start
613 * @return a new instant
614 */
615 public static AbsoluteDate createGPSDate(final int weekNumber,
616 final double milliInWeek) {
617 final int day = (int) FastMath.floor(milliInWeek / (1000.0 * Constants.JULIAN_DAY));
618 final double secondsInDay = milliInWeek / 1000.0 - day * Constants.JULIAN_DAY;
619 return new AbsoluteDate(new DateComponents(DateComponents.GPS_EPOCH, weekNumber * 7 + day),
620 new TimeComponents(secondsInDay),
621 TimeScalesFactory.getGPS());
622 }
623
624 /** Build an instance corresponding to a Julian Epoch (JE).
625 * <p>According to Lieske paper: <a
626 * href="http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?1979A%26A....73..282L&defaultprint=YES&filetype=.pdf.">
627 * Precession Matrix Based on IAU (1976) System of Astronomical Constants</a>, Astronomy and Astrophysics,
628 * vol. 73, no. 3, Mar. 1979, p. 282-284, Julian Epoch is related to Julian Ephemeris Date as:</p>
629 * <pre>
630 * JE = 2000.0 + (JED - 2451545.0) / 365.25
631 * </pre>
632 * <p>
633 * This method reverts the formula above and computes an {@code AbsoluteDate} from the Julian Epoch.
634 * </p>
635 * @param julianEpoch Julian epoch, like 2000.0 for defining the classical reference J2000.0
636 * @return a new instant
637 * @see #J2000_EPOCH
638 * @see #createBesselianEpoch(double)
639 */
640 public static AbsoluteDate createJulianEpoch(final double julianEpoch) {
641 return new AbsoluteDate(J2000_EPOCH,
642 Constants.JULIAN_YEAR * (julianEpoch - 2000.0));
643 }
644
645 /** Build an instance corresponding to a Besselian Epoch (BE).
646 * <p>According to Lieske paper: <a
647 * href="http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?1979A%26A....73..282L&defaultprint=YES&filetype=.pdf.">
648 * Precession Matrix Based on IAU (1976) System of Astronomical Constants</a>, Astronomy and Astrophysics,
649 * vol. 73, no. 3, Mar. 1979, p. 282-284, Besselian Epoch is related to Julian Ephemeris Date as:</p>
650 * <pre>
651 * BE = 1900.0 + (JED - 2415020.31352) / 365.242198781
652 * </pre>
653 * <p>
654 * This method reverts the formula above and computes an {@code AbsoluteDate} from the Besselian Epoch.
655 * </p>
656 * @param besselianEpoch Besselian epoch, like 1950 for defining the classical reference B1950.0
657 * @return a new instant
658 * @see #createJulianEpoch(double)
659 */
660 public static AbsoluteDate createBesselianEpoch(final double besselianEpoch) {
661 return new AbsoluteDate(J2000_EPOCH,
662 MathArrays.linearCombination(Constants.BESSELIAN_YEAR, besselianEpoch - 1900,
663 Constants.JULIAN_DAY, -36525,
664 Constants.JULIAN_DAY, 0.31352));
665 }
666
667 /** Get a time-shifted date.
668 * <p>
669 * Calling this method is equivalent to call <code>new AbsoluteDate(this, dt)</code>.
670 * </p>
671 * @param dt time shift in seconds
672 * @return a new date, shifted with respect to instance (which is immutable)
673 * @see org.orekit.utils.PVCoordinates#shiftedBy(double)
674 * @see org.orekit.attitudes.Attitude#shiftedBy(double)
675 * @see org.orekit.orbits.Orbit#shiftedBy(double)
676 * @see org.orekit.propagation.SpacecraftState#shiftedBy(double)
677 */
678 public AbsoluteDate shiftedBy(final double dt) {
679 return new AbsoluteDate(this, dt);
680 }
681
682 /** Compute the physically elapsed duration between two instants.
683 * <p>The returned duration is the number of seconds physically
684 * elapsed between the two instants, measured in a regular time
685 * scale with respect to surface of the Earth (i.e either the {@link
686 * TAIScale TAI scale}, the {@link TTScale TT scale} or the {@link
687 * GPSScale GPS scale}). It is the only method that gives a
688 * duration with a physical meaning.</p>
689 * <p>This method gives the same result (with less computation)
690 * as calling {@link #offsetFrom(AbsoluteDate, TimeScale)}
691 * with a second argument set to one of the regular scales cited
692 * above.</p>
693 * <p>This method is the reverse of the {@link #AbsoluteDate(AbsoluteDate,
694 * double)} constructor.</p>
695 * @param instant instant to subtract from the instance
696 * @return offset in seconds between the two instants (positive
697 * if the instance is posterior to the argument)
698 * @see #offsetFrom(AbsoluteDate, TimeScale)
699 * @see #AbsoluteDate(AbsoluteDate, double)
700 */
701 public double durationFrom(final AbsoluteDate instant) {
702 return (epoch - instant.epoch) + (offset - instant.offset);
703 }
704
705 /** Compute the apparent clock offset between two instant <em>in the
706 * perspective of a specific {@link TimeScale time scale}</em>.
707 * <p>The offset is the number of seconds counted in the given
708 * time scale between the locations of the two instants, with
709 * all time scale irregularities removed (i.e. considering all
710 * days are exactly 86400 seconds long). This method will give
711 * a result that may not have a physical meaning if the time scale
712 * is irregular. For example since a leap second was introduced at
713 * the end of 2005, the apparent offset between 2005-12-31T23:59:59
714 * and 2006-01-01T00:00:00 is 1 second, but the physical duration
715 * of the corresponding time interval as returned by the {@link
716 * #durationFrom(AbsoluteDate)} method is 2 seconds.</p>
717 * <p>This method is the reverse of the {@link #AbsoluteDate(AbsoluteDate,
718 * double, TimeScale)} constructor.</p>
719 * @param instant instant to subtract from the instance
720 * @param timeScale time scale with respect to which the offset should
721 * be computed
722 * @return apparent clock offset in seconds between the two instants
723 * (positive if the instance is posterior to the argument)
724 * @see #durationFrom(AbsoluteDate)
725 * @see #AbsoluteDate(AbsoluteDate, double, TimeScale)
726 */
727 public double offsetFrom(final AbsoluteDate instant, final TimeScale timeScale) {
728 final long elapsedDurationA = epoch - instant.epoch;
729 final double elapsedDurationB = (offset + timeScale.offsetFromTAI(this)) -
730 (instant.offset + timeScale.offsetFromTAI(instant));
731 return elapsedDurationA + elapsedDurationB;
732 }
733
734 /** Compute the offset between two time scales at the current instant.
735 * <p>The offset is defined as <i>l<sub>1</sub>-l<sub>2</sub></i>
736 * where <i>l<sub>1</sub></i> is the location of the instant in
737 * the <code>scale1</code> time scale and <i>l<sub>2</sub></i> is the
738 * location of the instant in the <code>scale2</code> time scale.</p>
739 * @param scale1 first time scale
740 * @param scale2 second time scale
741 * @return offset in seconds between the two time scales at the
742 * current instant
743 */
744 public double timeScalesOffset(final TimeScale scale1, final TimeScale scale2) {
745 return scale1.offsetFromTAI(this) - scale2.offsetFromTAI(this);
746 }
747
748 /** Convert the instance to a Java {@link java.util.Date Date}.
749 * <p>Conversion to the Date class induces a loss of precision because
750 * the Date class does not provide sub-millisecond information. Java Dates
751 * are considered to be locations in some times scales.</p>
752 * @param timeScale time scale to use
753 * @return a {@link java.util.Date Date} instance representing the location
754 * of the instant in the time scale
755 */
756 public Date toDate(final TimeScale timeScale) {
757 final double time = epoch + (offset + timeScale.offsetFromTAI(this));
758 return new Date(FastMath.round((time + 10957.5 * 86400.0) * 1000));
759 }
760
761 /** Split the instance into date/time components.
762 * @param timeScale time scale to use
763 * @return date/time components
764 */
765 public DateTimeComponents getComponents(final TimeScale timeScale) {
766
767 // compute offset from 2000-01-01T00:00:00 in specified time scale exactly,
768 // using Møller-Knuth TwoSum algorithm without branching
769 // the following statements must NOT be simplified, they rely on floating point
770 // arithmetic properties (rounding and representable numbers)
771 // at the end, the EXACT result of addition offset + timeScale.offsetFromTAI(this)
772 // is sum + residual, where sum is the closest representable number to the exact
773 // result and residual is the missing part that does not fit in the first number
774 final double taiOffset = timeScale.offsetFromTAI(this);
775 final double sum = offset + taiOffset;
776 final double oPrime = sum - taiOffset;
777 final double dPrime = sum - oPrime;
778 final double deltaO = offset - oPrime;
779 final double deltaD = taiOffset - dPrime;
780 final double residual = deltaO + deltaD;
781
782 // split date and time
783 final long carry = (long) FastMath.floor(sum);
784 double offset2000B = (sum - carry) + residual;
785 long offset2000A = epoch + carry + 43200l;
786 if (offset2000B < 0) {
787 offset2000A -= 1;
788 offset2000B += 1;
789 }
790 long time = offset2000A % 86400l;
791 if (time < 0l) {
792 time += 86400l;
793 }
794 final int date = (int) ((offset2000A - time) / 86400l);
795
796 // extract calendar elements
797 final DateComponents dateComponents = new DateComponents(DateComponents.J2000_EPOCH, date);
798 TimeComponents timeComponents = new TimeComponents((int) time, offset2000B);
799
800 if (timeScale instanceof UTCScale) {
801 final UTCScale utc = (UTCScale) timeScale;
802 if (utc.insideLeap(this)) {
803 // fix the seconds number to take the leap into account
804 timeComponents = new TimeComponents(timeComponents.getHour(), timeComponents.getMinute(),
805 timeComponents.getSecond() + utc.getLeap(this));
806 }
807 }
808
809 // build the components
810 return new DateTimeComponents(dateComponents, timeComponents);
811
812 }
813
814 /** Compare the instance with another date.
815 * @param date other date to compare the instance to
816 * @return a negative integer, zero, or a positive integer as this date
817 * is before, simultaneous, or after the specified date.
818 */
819 public int compareTo(final AbsoluteDate date) {
820 final double delta = durationFrom(date);
821 if (delta < 0) {
822 return -1;
823 } else if (delta > 0) {
824 return +1;
825 }
826 return 0;
827 }
828
829 /** {@inheritDoc} */
830 public AbsoluteDate getDate() {
831 return this;
832 }
833
834 /** Check if the instance represent the same time as another instance.
835 * @param date other date
836 * @return true if the instance and the other date refer to the same instant
837 */
838 public boolean equals(final Object date) {
839
840 if (date == this) {
841 // first fast check
842 return true;
843 }
844
845 if ((date != null) && (date instanceof AbsoluteDate)) {
846 return durationFrom((AbsoluteDate) date) == 0;
847 }
848
849 return false;
850
851 }
852
853 /** Get a hashcode for this date.
854 * @return hashcode
855 */
856 public int hashCode() {
857 final long l = Double.doubleToLongBits(durationFrom(J2000_EPOCH));
858 return (int) (l ^ (l >>> 32));
859 }
860
861 /** Get a String representation of the instant location in UTC time scale.
862 * @return a string representation of the instance,
863 * in ISO-8601 format with milliseconds accuracy
864 */
865 public String toString() {
866 try {
867 return toString(TimeScalesFactory.getUTC());
868 } catch (OrekitException oe) {
869 throw new RuntimeException(oe);
870 }
871 }
872
873 /** Get a String representation of the instant location.
874 * @param timeScale time scale to use
875 * @return a string representation of the instance,
876 * in ISO-8601 format with milliseconds accuracy
877 */
878 public String toString(final TimeScale timeScale) {
879 return getComponents(timeScale).toString();
880 }
881
882 }