AbsoluteDate.java
/* Copyright 2002-2015 CS Systèmes d'Information
* Licensed to CS Systèmes d'Information (CS) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* CS licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.orekit.time;
import java.io.Serializable;
import java.util.Date;
import org.apache.commons.math3.util.FastMath;
import org.apache.commons.math3.util.MathArrays;
import org.orekit.errors.OrekitException;
import org.orekit.errors.OrekitMessages;
import org.orekit.utils.Constants;
/** This class represents a specific instant in time.
* <p>Instances of this class are considered to be absolute in the sense
* that each one represent the occurrence of some event and can be compared
* to other instances or located in <em>any</em> {@link TimeScale time scale}. In
* other words the different locations of an event with respect to two different
* time scales (say {@link TAIScale TAI} and {@link UTCScale UTC} for example) are
* simply different perspective related to a single object. Only one
* <code>AbsoluteDate</code> instance is needed, both representations being available
* from this single instance by specifying the time scales as parameter when calling
* the ad-hoc methods.</p>
*
* <p>Since an instance is not bound to a specific time-scale, all methods related
* to the location of the date within some time scale require to provide the time
* scale as an argument. It is therefore possible to define a date in one time scale
* and to use it in another one. An example of such use is to read a date from a file
* in UTC and write it in another file in TAI. This can be done as follows:</p>
* <pre>
* DateTimeComponents utcComponents = readNextDate();
* AbsoluteDate date = new AbsoluteDate(utcComponents, TimeScalesFactory.getUTC());
* writeNextDate(date.getComponents(TimeScalesFactory.getTAI()));
* </pre>
*
* <p>Two complementary views are available:</p>
* <ul>
* <li><p>location view (mainly for input/output or conversions)</p>
* <p>locations represent the coordinate of one event with respect to a
* {@link TimeScale time scale}. The related methods are {@link
* #AbsoluteDate(DateComponents, TimeComponents, TimeScale)}, {@link
* #AbsoluteDate(int, int, int, int, int, double, TimeScale)}, {@link
* #AbsoluteDate(int, int, int, TimeScale)}, {@link #AbsoluteDate(Date,
* TimeScale)}, {@link #createGPSDate(int, double)}, {@link
* #parseCCSDSCalendarSegmentedTimeCode(byte, byte[])}, toString(){@link
* #toDate(TimeScale)}, {@link #toString(TimeScale) toString(timeScale)},
* {@link #toString()}, and {@link #timeScalesOffset}.</p>
* </li>
* <li><p>offset view (mainly for physical computation)</p>
* <p>offsets represent either the flow of time between two events
* (two instances of the class) or durations. They are counted in seconds,
* are continuous and could be measured using only a virtually perfect stopwatch.
* The related methods are {@link #AbsoluteDate(AbsoluteDate, double)},
* {@link #parseCCSDSUnsegmentedTimeCode(byte, byte, byte[], AbsoluteDate)},
* {@link #parseCCSDSDaySegmentedTimeCode(byte, byte[], DateComponents)},
* {@link #durationFrom(AbsoluteDate)}, {@link #compareTo(AbsoluteDate)}, {@link #equals(Object)}
* and {@link #hashCode()}.</p>
* </li>
* </ul>
* <p>
* A few reference epochs which are commonly used in space systems have been defined. These
* epochs can be used as the basis for offset computation. The supported epochs are:
* {@link #JULIAN_EPOCH}, {@link #MODIFIED_JULIAN_EPOCH}, {@link #FIFTIES_EPOCH},
* {@link #CCSDS_EPOCH}, {@link #GALILEO_EPOCH}, {@link #GPS_EPOCH}, {@link #J2000_EPOCH},
* {@link #JAVA_EPOCH}. There are also two factory methods {@link #createJulianEpoch(double)}
* and {@link #createBesselianEpoch(double)} that can be used to compute other reference
* epochs like J1900.0 or B1950.0.
* In addition to these reference epochs, two other constants are defined for convenience:
* {@link #PAST_INFINITY} and {@link #FUTURE_INFINITY}, which can be used either as dummy
* dates when a date is not yet initialized, or for initialization of loops searching for
* a min or max date.
* </p>
* <p>
* Instances of the <code>AbsoluteDate</code> class are guaranteed to be immutable.
* </p>
* @author Luc Maisonobe
* @see TimeScale
* @see TimeStamped
* @see ChronologicalComparator
*/
public class AbsoluteDate
implements TimeStamped, TimeShiftable<AbsoluteDate>, Comparable<AbsoluteDate>, Serializable {
/** Reference epoch for julian dates: -4712-01-01T12:00:00 Terrestrial Time.
* <p>Both <code>java.util.Date</code> and {@link DateComponents} classes
* follow the astronomical conventions and consider a year 0 between
* years -1 and +1, hence this reference date lies in year -4712 and not
* in year -4713 as can be seen in other documents or programs that obey
* a different convention (for example the <code>convcal</code> utility).</p>
*/
public static final AbsoluteDate JULIAN_EPOCH =
new AbsoluteDate(DateComponents.JULIAN_EPOCH, TimeComponents.H12, TimeScalesFactory.getTT());
/** Reference epoch for modified julian dates: 1858-11-17T00:00:00 Terrestrial Time. */
public static final AbsoluteDate MODIFIED_JULIAN_EPOCH =
new AbsoluteDate(DateComponents.MODIFIED_JULIAN_EPOCH, TimeComponents.H00, TimeScalesFactory.getTT());
/** Reference epoch for 1950 dates: 1950-01-01T00:00:00 Terrestrial Time. */
public static final AbsoluteDate FIFTIES_EPOCH =
new AbsoluteDate(DateComponents.FIFTIES_EPOCH, TimeComponents.H00, TimeScalesFactory.getTT());
/** Reference epoch for CCSDS Time Code Format (CCSDS 301.0-B-4):
* 1958-01-01T00:00:00 International Atomic Time (<em>not</em> UTC). */
public static final AbsoluteDate CCSDS_EPOCH =
new AbsoluteDate(DateComponents.CCSDS_EPOCH, TimeComponents.H00, TimeScalesFactory.getTAI());
/** Reference epoch for Galileo System Time: 1999-08-22T00:00:00 UTC. */
public static final AbsoluteDate GALILEO_EPOCH =
new AbsoluteDate(DateComponents.GALILEO_EPOCH, new TimeComponents(0, 0, 32),
TimeScalesFactory.getTAI());
/** Reference epoch for GPS weeks: 1980-01-06T00:00:00 GPS time. */
public static final AbsoluteDate GPS_EPOCH =
new AbsoluteDate(DateComponents.GPS_EPOCH, TimeComponents.H00, TimeScalesFactory.getGPS());
/** J2000.0 Reference epoch: 2000-01-01T12:00:00 Terrestrial Time (<em>not</em> UTC).
* @see #createJulianEpoch(double)
* @see #createBesselianEpoch(double)
*/
public static final AbsoluteDate J2000_EPOCH =
new AbsoluteDate(DateComponents.J2000_EPOCH, TimeComponents.H12, TimeScalesFactory.getTT());
/** Java Reference epoch: 1970-01-01T00:00:00 Universal Time Coordinate.
* <p>
* Between 1968-02-01 and 1972-01-01, UTC-TAI = 4.213 170 0s + (MJD - 39 126) x 0.002 592s.
* As on 1970-01-01 MJD = 40587, UTC-TAI = 8.000082s
* </p>
*/
public static final AbsoluteDate JAVA_EPOCH =
new AbsoluteDate(DateComponents.JAVA_EPOCH, TimeScalesFactory.getTAI()).shiftedBy(8.000082);
/** Dummy date at infinity in the past direction. */
public static final AbsoluteDate PAST_INFINITY = JAVA_EPOCH.shiftedBy(Double.NEGATIVE_INFINITY);
/** Dummy date at infinity in the future direction. */
public static final AbsoluteDate FUTURE_INFINITY = JAVA_EPOCH.shiftedBy(Double.POSITIVE_INFINITY);
/** Serializable UID. */
private static final long serialVersionUID = 617061803741806846L;
/** Reference epoch in seconds from 2000-01-01T12:00:00 TAI.
* <p>Beware, it is not {@link #J2000_EPOCH} since it is in TAI and not in TT.</p> */
private final long epoch;
/** Offset from the reference epoch in seconds. */
private final double offset;
/** Create an instance with a default value ({@link #J2000_EPOCH}).
*/
public AbsoluteDate() {
epoch = J2000_EPOCH.epoch;
offset = J2000_EPOCH.offset;
}
/** Build an instance from a location (parsed from a string) in a {@link TimeScale time scale}.
* <p>
* The supported formats for location are mainly the ones defined in ISO-8601 standard,
* the exact subset is explained in {@link DateTimeComponents#parseDateTime(String)},
* {@link DateComponents#parseDate(String)} and {@link TimeComponents#parseTime(String)}.
* </p>
* <p>
* As CCSDS ASCII calendar segmented time code is a trimmed down version of ISO-8601,
* it is also supported by this constructor.
* </p>
* @param location location in the time scale, must be in a supported format
* @param timeScale time scale
* @exception IllegalArgumentException if location string is not in a supported format
*/
public AbsoluteDate(final String location, final TimeScale timeScale) {
this(DateTimeComponents.parseDateTime(location), timeScale);
}
/** Build an instance from a location in a {@link TimeScale time scale}.
* @param location location in the time scale
* @param timeScale time scale
*/
public AbsoluteDate(final DateTimeComponents location, final TimeScale timeScale) {
this(location.getDate(), location.getTime(), timeScale);
}
/** Build an instance from a location in a {@link TimeScale time scale}.
* @param date date location in the time scale
* @param time time location in the time scale
* @param timeScale time scale
*/
public AbsoluteDate(final DateComponents date, final TimeComponents time,
final TimeScale timeScale) {
final double seconds = time.getSecond();
final double tsOffset = timeScale.offsetToTAI(date, time);
// compute sum exactly, using Møller-Knuth TwoSum algorithm without branching
// the following statements must NOT be simplified, they rely on floating point
// arithmetic properties (rounding and representable numbers)
// at the end, the EXACT result of addition seconds + tsOffset
// is sum + residual, where sum is the closest representable number to the exact
// result and residual is the missing part that does not fit in the first number
final double sum = seconds + tsOffset;
final double sPrime = sum - tsOffset;
final double tPrime = sum - sPrime;
final double deltaS = seconds - sPrime;
final double deltaT = tsOffset - tPrime;
final double residual = deltaS + deltaT;
final long dl = (long) FastMath.floor(sum);
offset = (sum - dl) + residual;
epoch = 60l * ((date.getJ2000Day() * 24l + time.getHour()) * 60l + time.getMinute() - 720l) + dl;
}
/** Build an instance from a location in a {@link TimeScale time scale}.
* @param year year number (may be 0 or negative for BC years)
* @param month month number from 1 to 12
* @param day day number from 1 to 31
* @param hour hour number from 0 to 23
* @param minute minute number from 0 to 59
* @param second second number from 0.0 to 60.0 (excluded)
* @param timeScale time scale
* @exception IllegalArgumentException if inconsistent arguments
* are given (parameters out of range)
*/
public AbsoluteDate(final int year, final int month, final int day,
final int hour, final int minute, final double second,
final TimeScale timeScale) throws IllegalArgumentException {
this(new DateComponents(year, month, day), new TimeComponents(hour, minute, second), timeScale);
}
/** Build an instance from a location in a {@link TimeScale time scale}.
* @param year year number (may be 0 or negative for BC years)
* @param month month enumerate
* @param day day number from 1 to 31
* @param hour hour number from 0 to 23
* @param minute minute number from 0 to 59
* @param second second number from 0.0 to 60.0 (excluded)
* @param timeScale time scale
* @exception IllegalArgumentException if inconsistent arguments
* are given (parameters out of range)
*/
public AbsoluteDate(final int year, final Month month, final int day,
final int hour, final int minute, final double second,
final TimeScale timeScale) throws IllegalArgumentException {
this(new DateComponents(year, month, day), new TimeComponents(hour, minute, second), timeScale);
}
/** Build an instance from a location in a {@link TimeScale time scale}.
* <p>The hour is set to 00:00:00.000.</p>
* @param date date location in the time scale
* @param timeScale time scale
* @exception IllegalArgumentException if inconsistent arguments
* are given (parameters out of range)
*/
public AbsoluteDate(final DateComponents date, final TimeScale timeScale)
throws IllegalArgumentException {
this(date, TimeComponents.H00, timeScale);
}
/** Build an instance from a location in a {@link TimeScale time scale}.
* <p>The hour is set to 00:00:00.000.</p>
* @param year year number (may be 0 or negative for BC years)
* @param month month number from 1 to 12
* @param day day number from 1 to 31
* @param timeScale time scale
* @exception IllegalArgumentException if inconsistent arguments
* are given (parameters out of range)
*/
public AbsoluteDate(final int year, final int month, final int day,
final TimeScale timeScale) throws IllegalArgumentException {
this(new DateComponents(year, month, day), TimeComponents.H00, timeScale);
}
/** Build an instance from a location in a {@link TimeScale time scale}.
* <p>The hour is set to 00:00:00.000.</p>
* @param year year number (may be 0 or negative for BC years)
* @param month month enumerate
* @param day day number from 1 to 31
* @param timeScale time scale
* @exception IllegalArgumentException if inconsistent arguments
* are given (parameters out of range)
*/
public AbsoluteDate(final int year, final Month month, final int day,
final TimeScale timeScale) throws IllegalArgumentException {
this(new DateComponents(year, month, day), TimeComponents.H00, timeScale);
}
/** Build an instance from a location in a {@link TimeScale time scale}.
* @param location location in the time scale
* @param timeScale time scale
*/
public AbsoluteDate(final Date location, final TimeScale timeScale) {
this(new DateComponents(DateComponents.JAVA_EPOCH,
(int) (location.getTime() / 86400000l)),
new TimeComponents(0.001 * (location.getTime() % 86400000l)),
timeScale);
}
/** Build an instance from an elapsed duration since to another instant.
* <p>It is important to note that the elapsed duration is <em>not</em>
* the difference between two readings on a time scale. As an example,
* the duration between the two instants leading to the readings
* 2005-12-31T23:59:59 and 2006-01-01T00:00:00 in the {@link UTCScale UTC}
* time scale is <em>not</em> 1 second, but a stop watch would have measured
* an elapsed duration of 2 seconds between these two instances because a leap
* second was introduced at the end of 2005 in this time scale.</p>
* <p>This constructor is the reverse of the {@link #durationFrom(AbsoluteDate)}
* method.</p>
* @param since start instant of the measured duration
* @param elapsedDuration physically elapsed duration from the <code>since</code>
* instant, as measured in a regular time scale
* @see #durationFrom(AbsoluteDate)
*/
public AbsoluteDate(final AbsoluteDate since, final double elapsedDuration) {
final double sum = since.offset + elapsedDuration;
if (Double.isInfinite(sum)) {
offset = sum;
epoch = (sum < 0) ? Long.MIN_VALUE : Long.MAX_VALUE;
} else {
// compute sum exactly, using Møller-Knuth TwoSum algorithm without branching
// the following statements must NOT be simplified, they rely on floating point
// arithmetic properties (rounding and representable numbers)
// at the end, the EXACT result of addition since.offset + elapsedDuration
// is sum + residual, where sum is the closest representable number to the exact
// result and residual is the missing part that does not fit in the first number
final double oPrime = sum - elapsedDuration;
final double dPrime = sum - oPrime;
final double deltaO = since.offset - oPrime;
final double deltaD = elapsedDuration - dPrime;
final double residual = deltaO + deltaD;
final long dl = (long) FastMath.floor(sum);
offset = (sum - dl) + residual;
epoch = since.epoch + dl;
}
}
/** Build an instance from an apparent clock offset with respect to another
* instant <em>in the perspective of a specific {@link TimeScale time scale}</em>.
* <p>It is important to note that the apparent clock offset <em>is</em> the
* difference between two readings on a time scale and <em>not</em> an elapsed
* duration. As an example, the apparent clock offset between the two instants
* leading to the readings 2005-12-31T23:59:59 and 2006-01-01T00:00:00 in the
* {@link UTCScale UTC} time scale is 1 second, but the elapsed duration is 2
* seconds because a leap second has been introduced at the end of 2005 in this
* time scale.</p>
* <p>This constructor is the reverse of the {@link #offsetFrom(AbsoluteDate,
* TimeScale)} method.</p>
* @param reference reference instant
* @param apparentOffset apparent clock offset from the reference instant
* (difference between two readings in the specified time scale)
* @param timeScale time scale with respect to which the offset is defined
* @see #offsetFrom(AbsoluteDate, TimeScale)
*/
public AbsoluteDate(final AbsoluteDate reference, final double apparentOffset,
final TimeScale timeScale) {
this(new DateTimeComponents(reference.getComponents(timeScale), apparentOffset),
timeScale);
}
/** Build an instance from a CCSDS Unsegmented Time Code (CUC).
* <p>
* CCSDS Unsegmented Time Code is defined in the blue book:
* CCSDS Time Code Format (CCSDS 301.0-B-4) published in November 2010
* </p>
* <p>
* If the date to be parsed is formatted using version 3 of the standard
* (CCSDS 301.0-B-3 published in 2002) or if the extension of the preamble
* field introduced in version 4 of the standard is not used, then the
* {@code preambleField2} parameter can be set to 0.
* </p>
* @param preambleField1 first byte of the field specifying the format, often
* not transmitted in data interfaces, as it is constant for a given data interface
* @param preambleField2 second byte of the field specifying the format
* (added in revision 4 of the CCSDS standard in 2010), often not transmitted in data
* interfaces, as it is constant for a given data interface (value ignored if presence
* not signaled in {@code preambleField1})
* @param timeField byte array containing the time code
* @param agencyDefinedEpoch reference epoch, ignored if the preamble field
* specifies the {@link #CCSDS_EPOCH CCSDS reference epoch} is used (and hence
* may be null in this case)
* @return an instance corresponding to the specified date
* @throws OrekitException if preamble is inconsistent with Unsegmented Time Code,
* or if it is inconsistent with time field, or if agency epoch is needed but not provided
*/
public static AbsoluteDate parseCCSDSUnsegmentedTimeCode(final byte preambleField1,
final byte preambleField2,
final byte[] timeField,
final AbsoluteDate agencyDefinedEpoch)
throws OrekitException {
// time code identification and reference epoch
final AbsoluteDate epoch;
switch (preambleField1 & 0x70) {
case 0x10:
// the reference epoch is CCSDS epoch 1958-01-01T00:00:00 TAI
epoch = CCSDS_EPOCH;
break;
case 0x20:
// the reference epoch is agency defined
if (agencyDefinedEpoch == null) {
throw new OrekitException(OrekitMessages.CCSDS_DATE_MISSING_AGENCY_EPOCH);
}
epoch = agencyDefinedEpoch;
break;
default :
throw new OrekitException(OrekitMessages.CCSDS_DATE_INVALID_PREAMBLE_FIELD,
formatByte(preambleField1));
}
// time field lengths
int coarseTimeLength = 1 + ((preambleField1 & 0x0C) >>> 2);
int fineTimeLength = preambleField1 & 0x03;
if ((preambleField1 & 0x80) != 0x0) {
// there is an additional octet in preamble field
coarseTimeLength += (preambleField2 & 0x60) >>> 5;
fineTimeLength += (preambleField2 & 0x1C) >>> 2;
}
if (timeField.length != coarseTimeLength + fineTimeLength) {
throw new OrekitException(OrekitMessages.CCSDS_DATE_INVALID_LENGTH_TIME_FIELD,
timeField.length, coarseTimeLength + fineTimeLength);
}
double seconds = 0;
for (int i = 0; i < coarseTimeLength; ++i) {
seconds = seconds * 256 + toUnsigned(timeField[i]);
}
double subseconds = 0;
for (int i = timeField.length - 1; i >= coarseTimeLength; --i) {
subseconds = (subseconds + toUnsigned(timeField[i])) / 256;
}
return new AbsoluteDate(epoch, seconds).shiftedBy(subseconds);
}
/** Build an instance from a CCSDS Day Segmented Time Code (CDS).
* <p>
* CCSDS Day Segmented Time Code is defined in the blue book:
* CCSDS Time Code Format (CCSDS 301.0-B-4) published in November 2010
* </p>
* @param preambleField field specifying the format, often not transmitted in
* data interfaces, as it is constant for a given data interface
* @param timeField byte array containing the time code
* @param agencyDefinedEpoch reference epoch, ignored if the preamble field
* specifies the {@link #CCSDS_EPOCH CCSDS reference epoch} is used (and hence
* may be null in this case)
* @return an instance corresponding to the specified date
* @throws OrekitException if preamble is inconsistent with Day Segmented Time Code,
* or if it is inconsistent with time field, or if agency epoch is needed but not provided,
* or it UTC time scale cannot be retrieved
*/
public static AbsoluteDate parseCCSDSDaySegmentedTimeCode(final byte preambleField, final byte[] timeField,
final DateComponents agencyDefinedEpoch)
throws OrekitException {
// time code identification
if ((preambleField & 0xF0) != 0x40) {
throw new OrekitException(OrekitMessages.CCSDS_DATE_INVALID_PREAMBLE_FIELD,
formatByte(preambleField));
}
// reference epoch
final DateComponents epoch;
if ((preambleField & 0x08) == 0x00) {
// the reference epoch is CCSDS epoch 1958-01-01T00:00:00 TAI
epoch = DateComponents.CCSDS_EPOCH;
} else {
// the reference epoch is agency defined
if (agencyDefinedEpoch == null) {
throw new OrekitException(OrekitMessages.CCSDS_DATE_MISSING_AGENCY_EPOCH);
}
epoch = agencyDefinedEpoch;
}
// time field lengths
final int daySegmentLength = ((preambleField & 0x04) == 0x0) ? 2 : 3;
final int subMillisecondLength = (preambleField & 0x03) << 1;
if (subMillisecondLength == 6) {
throw new OrekitException(OrekitMessages.CCSDS_DATE_INVALID_PREAMBLE_FIELD,
formatByte(preambleField));
}
if (timeField.length != daySegmentLength + 4 + subMillisecondLength) {
throw new OrekitException(OrekitMessages.CCSDS_DATE_INVALID_LENGTH_TIME_FIELD,
timeField.length, daySegmentLength + 4 + subMillisecondLength);
}
int i = 0;
int day = 0;
while (i < daySegmentLength) {
day = day * 256 + toUnsigned(timeField[i++]);
}
long milliInDay = 0l;
while (i < daySegmentLength + 4) {
milliInDay = milliInDay * 256 + toUnsigned(timeField[i++]);
}
final int milli = (int) (milliInDay % 1000l);
final int seconds = (int) ((milliInDay - milli) / 1000l);
double subMilli = 0;
double divisor = 1;
while (i < timeField.length) {
subMilli = subMilli * 256 + toUnsigned(timeField[i++]);
divisor *= 1000;
}
final DateComponents date = new DateComponents(epoch, day);
final TimeComponents time = new TimeComponents(seconds);
return new AbsoluteDate(date, time, TimeScalesFactory.getUTC()).shiftedBy(milli * 1.0e-3 + subMilli / divisor);
}
/** Build an instance from a CCSDS Calendar Segmented Time Code (CCS).
* <p>
* CCSDS Calendar Segmented Time Code is defined in the blue book:
* CCSDS Time Code Format (CCSDS 301.0-B-4) published in November 2010
* </p>
* @param preambleField field specifying the format, often not transmitted in
* data interfaces, as it is constant for a given data interface
* @param timeField byte array containing the time code
* @return an instance corresponding to the specified date
* @throws OrekitException if preamble is inconsistent with Calendar Segmented Time Code,
* or if it is inconsistent with time field, or it UTC time scale cannot be retrieved
*/
public static AbsoluteDate parseCCSDSCalendarSegmentedTimeCode(final byte preambleField, final byte[] timeField)
throws OrekitException {
// time code identification
if ((preambleField & 0xF0) != 0x50) {
throw new OrekitException(OrekitMessages.CCSDS_DATE_INVALID_PREAMBLE_FIELD,
formatByte(preambleField));
}
// time field length
final int length = 7 + (preambleField & 0x07);
if (length == 14) {
throw new OrekitException(OrekitMessages.CCSDS_DATE_INVALID_PREAMBLE_FIELD,
formatByte(preambleField));
}
if (timeField.length != length) {
throw new OrekitException(OrekitMessages.CCSDS_DATE_INVALID_LENGTH_TIME_FIELD,
timeField.length, length);
}
// date part in the first four bytes
final DateComponents date;
if ((preambleField & 0x08) == 0x00) {
// month of year and day of month variation
date = new DateComponents(toUnsigned(timeField[0]) * 256 + toUnsigned(timeField[1]),
toUnsigned(timeField[2]),
toUnsigned(timeField[3]));
} else {
// day of year variation
date = new DateComponents(toUnsigned(timeField[0]) * 256 + toUnsigned(timeField[1]),
toUnsigned(timeField[2]) * 256 + toUnsigned(timeField[3]));
}
// time part from bytes 5 to last (between 7 and 13 depending on precision)
final TimeComponents time = new TimeComponents(toUnsigned(timeField[4]),
toUnsigned(timeField[5]),
toUnsigned(timeField[6]));
double subSecond = 0;
double divisor = 1;
for (int i = 7; i < length; ++i) {
subSecond = subSecond * 100 + toUnsigned(timeField[i]);
divisor *= 100;
}
return new AbsoluteDate(date, time, TimeScalesFactory.getUTC()).shiftedBy(subSecond / divisor);
}
/** Decode a signed byte as an unsigned int value.
* @param b byte to decode
* @return an unsigned int value
*/
private static int toUnsigned(final byte b) {
final int i = (int) b;
return (i < 0) ? 256 + i : i;
}
/** Format a byte as an hex string for error messages.
* @param data byte to format
* @return a formatted string
*/
private static String formatByte(final byte data) {
return "0x" + Integer.toHexString(data).toUpperCase();
}
/** Build an instance corresponding to a GPS date.
* <p>GPS dates are provided as a week number starting at
* {@link #GPS_EPOCH GPS epoch} and as a number of milliseconds
* since week start.</p>
* @param weekNumber week number since {@link #GPS_EPOCH GPS epoch}
* @param milliInWeek number of milliseconds since week start
* @return a new instant
*/
public static AbsoluteDate createGPSDate(final int weekNumber,
final double milliInWeek) {
final int day = (int) FastMath.floor(milliInWeek / (1000.0 * Constants.JULIAN_DAY));
final double secondsInDay = milliInWeek / 1000.0 - day * Constants.JULIAN_DAY;
return new AbsoluteDate(new DateComponents(DateComponents.GPS_EPOCH, weekNumber * 7 + day),
new TimeComponents(secondsInDay),
TimeScalesFactory.getGPS());
}
/** Build an instance corresponding to a Julian Epoch (JE).
* <p>According to Lieske paper: <a
* href="http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?1979A%26A....73..282L&defaultprint=YES&filetype=.pdf.">
* Precession Matrix Based on IAU (1976) System of Astronomical Constants</a>, Astronomy and Astrophysics,
* vol. 73, no. 3, Mar. 1979, p. 282-284, Julian Epoch is related to Julian Ephemeris Date as:</p>
* <pre>
* JE = 2000.0 + (JED - 2451545.0) / 365.25
* </pre>
* <p>
* This method reverts the formula above and computes an {@code AbsoluteDate} from the Julian Epoch.
* </p>
* @param julianEpoch Julian epoch, like 2000.0 for defining the classical reference J2000.0
* @return a new instant
* @see #J2000_EPOCH
* @see #createBesselianEpoch(double)
*/
public static AbsoluteDate createJulianEpoch(final double julianEpoch) {
return new AbsoluteDate(J2000_EPOCH,
Constants.JULIAN_YEAR * (julianEpoch - 2000.0));
}
/** Build an instance corresponding to a Besselian Epoch (BE).
* <p>According to Lieske paper: <a
* href="http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?1979A%26A....73..282L&defaultprint=YES&filetype=.pdf.">
* Precession Matrix Based on IAU (1976) System of Astronomical Constants</a>, Astronomy and Astrophysics,
* vol. 73, no. 3, Mar. 1979, p. 282-284, Besselian Epoch is related to Julian Ephemeris Date as:</p>
* <pre>
* BE = 1900.0 + (JED - 2415020.31352) / 365.242198781
* </pre>
* <p>
* This method reverts the formula above and computes an {@code AbsoluteDate} from the Besselian Epoch.
* </p>
* @param besselianEpoch Besselian epoch, like 1950 for defining the classical reference B1950.0
* @return a new instant
* @see #createJulianEpoch(double)
*/
public static AbsoluteDate createBesselianEpoch(final double besselianEpoch) {
return new AbsoluteDate(J2000_EPOCH,
MathArrays.linearCombination(Constants.BESSELIAN_YEAR, besselianEpoch - 1900,
Constants.JULIAN_DAY, -36525,
Constants.JULIAN_DAY, 0.31352));
}
/** Get a time-shifted date.
* <p>
* Calling this method is equivalent to call <code>new AbsoluteDate(this, dt)</code>.
* </p>
* @param dt time shift in seconds
* @return a new date, shifted with respect to instance (which is immutable)
* @see org.orekit.utils.PVCoordinates#shiftedBy(double)
* @see org.orekit.attitudes.Attitude#shiftedBy(double)
* @see org.orekit.orbits.Orbit#shiftedBy(double)
* @see org.orekit.propagation.SpacecraftState#shiftedBy(double)
*/
public AbsoluteDate shiftedBy(final double dt) {
return new AbsoluteDate(this, dt);
}
/** Compute the physically elapsed duration between two instants.
* <p>The returned duration is the number of seconds physically
* elapsed between the two instants, measured in a regular time
* scale with respect to surface of the Earth (i.e either the {@link
* TAIScale TAI scale}, the {@link TTScale TT scale} or the {@link
* GPSScale GPS scale}). It is the only method that gives a
* duration with a physical meaning.</p>
* <p>This method gives the same result (with less computation)
* as calling {@link #offsetFrom(AbsoluteDate, TimeScale)}
* with a second argument set to one of the regular scales cited
* above.</p>
* <p>This method is the reverse of the {@link #AbsoluteDate(AbsoluteDate,
* double)} constructor.</p>
* @param instant instant to subtract from the instance
* @return offset in seconds between the two instants (positive
* if the instance is posterior to the argument)
* @see #offsetFrom(AbsoluteDate, TimeScale)
* @see #AbsoluteDate(AbsoluteDate, double)
*/
public double durationFrom(final AbsoluteDate instant) {
return (epoch - instant.epoch) + (offset - instant.offset);
}
/** Compute the apparent clock offset between two instant <em>in the
* perspective of a specific {@link TimeScale time scale}</em>.
* <p>The offset is the number of seconds counted in the given
* time scale between the locations of the two instants, with
* all time scale irregularities removed (i.e. considering all
* days are exactly 86400 seconds long). This method will give
* a result that may not have a physical meaning if the time scale
* is irregular. For example since a leap second was introduced at
* the end of 2005, the apparent offset between 2005-12-31T23:59:59
* and 2006-01-01T00:00:00 is 1 second, but the physical duration
* of the corresponding time interval as returned by the {@link
* #durationFrom(AbsoluteDate)} method is 2 seconds.</p>
* <p>This method is the reverse of the {@link #AbsoluteDate(AbsoluteDate,
* double, TimeScale)} constructor.</p>
* @param instant instant to subtract from the instance
* @param timeScale time scale with respect to which the offset should
* be computed
* @return apparent clock offset in seconds between the two instants
* (positive if the instance is posterior to the argument)
* @see #durationFrom(AbsoluteDate)
* @see #AbsoluteDate(AbsoluteDate, double, TimeScale)
*/
public double offsetFrom(final AbsoluteDate instant, final TimeScale timeScale) {
final long elapsedDurationA = epoch - instant.epoch;
final double elapsedDurationB = (offset + timeScale.offsetFromTAI(this)) -
(instant.offset + timeScale.offsetFromTAI(instant));
return elapsedDurationA + elapsedDurationB;
}
/** Compute the offset between two time scales at the current instant.
* <p>The offset is defined as <i>l₁-l₂</i>
* where <i>l₁</i> is the location of the instant in
* the <code>scale1</code> time scale and <i>l₂</i> is the
* location of the instant in the <code>scale2</code> time scale.</p>
* @param scale1 first time scale
* @param scale2 second time scale
* @return offset in seconds between the two time scales at the
* current instant
*/
public double timeScalesOffset(final TimeScale scale1, final TimeScale scale2) {
return scale1.offsetFromTAI(this) - scale2.offsetFromTAI(this);
}
/** Convert the instance to a Java {@link java.util.Date Date}.
* <p>Conversion to the Date class induces a loss of precision because
* the Date class does not provide sub-millisecond information. Java Dates
* are considered to be locations in some times scales.</p>
* @param timeScale time scale to use
* @return a {@link java.util.Date Date} instance representing the location
* of the instant in the time scale
*/
public Date toDate(final TimeScale timeScale) {
final double time = epoch + (offset + timeScale.offsetFromTAI(this));
return new Date(FastMath.round((time + 10957.5 * 86400.0) * 1000));
}
/** Split the instance into date/time components.
* @param timeScale time scale to use
* @return date/time components
*/
public DateTimeComponents getComponents(final TimeScale timeScale) {
// compute offset from 2000-01-01T00:00:00 in specified time scale exactly,
// using Møller-Knuth TwoSum algorithm without branching
// the following statements must NOT be simplified, they rely on floating point
// arithmetic properties (rounding and representable numbers)
// at the end, the EXACT result of addition offset + timeScale.offsetFromTAI(this)
// is sum + residual, where sum is the closest representable number to the exact
// result and residual is the missing part that does not fit in the first number
final double taiOffset = timeScale.offsetFromTAI(this);
final double sum = offset + taiOffset;
final double oPrime = sum - taiOffset;
final double dPrime = sum - oPrime;
final double deltaO = offset - oPrime;
final double deltaD = taiOffset - dPrime;
final double residual = deltaO + deltaD;
// split date and time
final long carry = (long) FastMath.floor(sum);
double offset2000B = (sum - carry) + residual;
long offset2000A = epoch + carry + 43200l;
if (offset2000B < 0) {
offset2000A -= 1;
offset2000B += 1;
}
long time = offset2000A % 86400l;
if (time < 0l) {
time += 86400l;
}
final int date = (int) ((offset2000A - time) / 86400l);
// extract calendar elements
final DateComponents dateComponents = new DateComponents(DateComponents.J2000_EPOCH, date);
TimeComponents timeComponents = new TimeComponents((int) time, offset2000B);
if (timeScale instanceof UTCScale) {
final UTCScale utc = (UTCScale) timeScale;
if (utc.insideLeap(this)) {
// fix the seconds number to take the leap into account
timeComponents = new TimeComponents(timeComponents.getHour(), timeComponents.getMinute(),
timeComponents.getSecond() + utc.getLeap(this));
}
}
// build the components
return new DateTimeComponents(dateComponents, timeComponents);
}
/** Compare the instance with another date.
* @param date other date to compare the instance to
* @return a negative integer, zero, or a positive integer as this date
* is before, simultaneous, or after the specified date.
*/
public int compareTo(final AbsoluteDate date) {
final double delta = durationFrom(date);
if (delta < 0) {
return -1;
} else if (delta > 0) {
return +1;
}
return 0;
}
/** {@inheritDoc} */
public AbsoluteDate getDate() {
return this;
}
/** Check if the instance represent the same time as another instance.
* @param date other date
* @return true if the instance and the other date refer to the same instant
*/
public boolean equals(final Object date) {
if (date == this) {
// first fast check
return true;
}
if ((date != null) && (date instanceof AbsoluteDate)) {
return durationFrom((AbsoluteDate) date) == 0;
}
return false;
}
/** Get a hashcode for this date.
* @return hashcode
*/
public int hashCode() {
final long l = Double.doubleToLongBits(durationFrom(J2000_EPOCH));
return (int) (l ^ (l >>> 32));
}
/** Get a String representation of the instant location in UTC time scale.
* @return a string representation of the instance,
* in ISO-8601 format with milliseconds accuracy
*/
public String toString() {
try {
return toString(TimeScalesFactory.getUTC());
} catch (OrekitException oe) {
throw new RuntimeException(oe);
}
}
/** Get a String representation of the instant location.
* @param timeScale time scale to use
* @return a string representation of the instance,
* in ISO-8601 format with milliseconds accuracy
*/
public String toString(final TimeScale timeScale) {
return getComponents(timeScale).toString();
}
}