FieldAbsoluteDate.java

  1. /* Copyright 2002-2019 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;

  19. import java.util.Date;
  20. import java.util.TimeZone;

  22. import org.hipparchus.Field;
  23. import org.hipparchus.RealFieldElement;
  24. import org.hipparchus.util.FastMath;
  25. import org.orekit.errors.OrekitException;
  26. import org.orekit.errors.OrekitMessages;
  27. import org.orekit.utils.Constants;

  29. /** This class represents a specific instant in time.

  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>FieldAbsoluteDate<T></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.  *   FieldAbsoluteDate&lt;T&gt; date = new FieldAbsoluteDate&lt;&gt;(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.  *   #FieldAbsoluteDate(Field, DateComponents, TimeComponents, TimeScale)}, {@link
  58.  *   #FieldAbsoluteDate(Field, int, int, int, int, int, double, TimeScale)}, {@link
  59.  *   #FieldAbsoluteDate(Field, int, int, int, TimeScale)}, {@link #FieldAbsoluteDate(Field,
  60.  *   Date, TimeScale)}, {@link #createGPSDate(int, RealFieldElement)}, {@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 #FieldAbsoluteDate(FieldAbsoluteDate, double)},
  70.  *   {@link #parseCCSDSUnsegmentedTimeCode(Field, byte, byte, byte[], FieldAbsoluteDate)},
  71.  *   {@link #parseCCSDSDaySegmentedTimeCode(Field, byte, byte[], DateComponents)},
  72.  *   {@link #durationFrom(FieldAbsoluteDate)}, {@link #compareTo(FieldAbsoluteDate)}, {@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 #getJulianEpoch(Field)}, {@link #getModifiedJulianEpoch(Field)}, {@link #getFiftiesEpoch(Field)},
  80.  * {@link #getCCSDSEpoch(Field)}, {@link #getGalileoEpoch(Field)}, {@link #getGPSEpoch(Field)},
  81.  * {@link #getJ2000Epoch(Field)}, {@link #getJavaEpoch(Field)}. There are also two factory methods
  82.  * {@link #createJulianEpoch(RealFieldElement)} and {@link #createBesselianEpoch(RealFieldElement)}
  83.  * that can be used to compute other reference epochs like J1900.0 or B1950.0.
  84.  * In addition to these reference epochs, two other constants are defined for convenience:
  85.  * {@link #getPastInfinity(Field)} and {@link #getFutureInfinity(Field)}, which can be used either
  86.  * as dummy 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>FieldAbsoluteDate<T></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 FieldAbsoluteDate<T extends RealFieldElement<T>>
  98.     implements FieldTimeStamped<T>, TimeShiftable<FieldAbsoluteDate<T>>, Comparable<FieldAbsoluteDate<T>> {

  100.     /** Reference epoch in seconds from 2000-01-01T12:00:00 TAI.
  101.      * <p>Beware, it is not {@link #getJ2000Epoch(Field)} since it is in TAI and not in TT.</p> */
  102.     private final long epoch;

  104.     /** Offset from the reference epoch in seconds. */
  105.     private final  T offset;

  107.     /** Field used by default.*/
  108.     private Field<T> field;

  110.     /** Build an instance from an AbsoluteDate.
  111.      * @param field used by default
  112.      * @param date AbsoluteDate to instantiate as a FieldAbsoluteDate
  113.      */
  114.     public FieldAbsoluteDate(final Field<T> field, final AbsoluteDate date) {
  115.         this.field  = field;
  116.         this.epoch  = date.getEpoch();
  117.         this.offset = field.getZero().add(date.getOffset());
  118.     }

  120.     /** Create an instance with a default value ({@link #getJ2000Epoch(Field)}).
  121.      * @param field field used by default
  122.      */
  123.     public FieldAbsoluteDate(final Field<T> field) {
  124.         final FieldAbsoluteDate<T> j2000 = getJ2000Epoch(field);
  125.         this.field  = j2000.field;
  126.         this.epoch  = j2000.epoch;
  127.         this.offset = j2000.offset;
  128.     }

  130.     /** Build an instance from an elapsed duration since to another instant.
  131.      * <p>It is important to note that the elapsed duration is <em>not</em>
  132.      * the difference between two readings on a time scale. As an example,
  133.      * the duration between the two instants leading to the readings
  134.      * 2005-12-31T23:59:59 and 2006-01-01T00:00:00 in the {@link UTCScale UTC}
  135.      * time scale is <em>not</em> 1 second, but a stop watch would have measured
  136.      * an elapsed duration of 2 seconds between these two instances because a leap
  137.      * second was introduced at the end of 2005 in this time scale.</p>
  138.      * <p>This constructor is the reverse of the {@link #durationFrom(FieldAbsoluteDate)}
  139.      * method.</p>
  140.      * @param since start instant of the measured duration
  141.      * @param elapsedDuration physically elapsed duration from the <code>since</code>
  142.      * instant, as measured in a regular time scale
  143.      * @see #durationFrom(FieldAbsoluteDate)
  144.      */
  145.     public FieldAbsoluteDate(final FieldAbsoluteDate<T> since, final T elapsedDuration) {
  146.         this.field = since.field;
  147.         final T sum = since.offset.add(elapsedDuration);
  148.         if (Double.isInfinite(sum.getReal())) {
  149.             offset = sum;
  150.             epoch  = (sum.getReal() < 0) ? Long.MIN_VALUE : Long.MAX_VALUE;
  151.         } else {
  152.             // compute sum exactly, using Møller-Knuth TwoSum algorithm without branching
  153.             // the following statements must NOT be simplified, they rely on floating point
  154.             // arithmetic properties (rounding and representable numbers)
  155.             // at the end, the EXACT result of addition since.offset + elapsedDuration
  156.             // is sum + residual, where sum is the closest representable number to the exact
  157.             // result and residual is the missing part that does not fit in the first number
  158.             final double oPrime   = sum.getReal() - elapsedDuration.getReal();
  159.             final double dPrime   = sum.getReal() - oPrime;
  160.             final double deltaO   = since.offset.getReal() - oPrime;
  161.             final double deltaD   = elapsedDuration.getReal() - dPrime;
  162.             final double residual = deltaO + deltaD;
  163.             final long   dl       = (long) FastMath.floor(sum.getReal());
  164.             offset = sum.subtract(dl).add(residual);
  165.             epoch  = since.epoch + dl;
  166.         }
  167.     }

  169.     /** Build an instance from a location (parsed from a string) in a {@link TimeScale time scale}.
  170.      * <p>
  171.      * The supported formats for location are mainly the ones defined in ISO-8601 standard,
  172.      * the exact subset is explained in {@link DateTimeComponents#parseDateTime(String)},
  173.      * {@link DateComponents#parseDate(String)} and {@link TimeComponents#parseTime(String)}.
  174.      * </p>
  175.      * <p>
  176.      * As CCSDS ASCII calendar segmented time code is a trimmed down version of ISO-8601,
  177.      * it is also supported by this constructor.
  178.      * </p>
  179.      * @param field field utilized by default
  180.      * @param location location in the time scale, must be in a supported format
  181.      * @param timeScale time scale
  182.      * @exception IllegalArgumentException if location string is not in a supported format
  183.      */
  184.     public FieldAbsoluteDate(final Field<T> field, final String location, final TimeScale timeScale) {
  185.         this(field, DateTimeComponents.parseDateTime(location), timeScale);
  186.     }

  188.     /** Build an instance from a location in a {@link TimeScale time scale}.
  189.      * @param field field utilized by default
  190.      * @param location location in the time scale
  191.      * @param timeScale time scale
  192.      */
  193.     public FieldAbsoluteDate(final Field<T> field, final DateTimeComponents location, final TimeScale timeScale) {
  194.         this(field, location.getDate(), location.getTime(), timeScale);
  195.     }

  197.     /** Build an instance from a location in a {@link TimeScale time scale}.
  198.      * @param field field utilized by default
  199.      * @param date date location in the time scale
  200.      * @param time time location in the time scale
  201.      * @param timeScale time scale
  202.      */
  203.     public FieldAbsoluteDate(final Field<T> field, final DateComponents date, final TimeComponents time,
  204.                              final TimeScale timeScale) {
  205.         final double seconds  = time.getSecond();
  206.         final double tsOffset = timeScale.offsetToTAI(date, time);

  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);

  222.         offset = field.getZero().add((sum - dl) + residual);

  224.         epoch  = 60l * ((date.getJ2000Day() * 24l + time.getHour()) * 60l +
  225.                         time.getMinute() - time.getMinutesFromUTC() - 720l) + dl;
  226.         this.field = field;

  228.     }

  230.     /** Build an instance from a location in a {@link TimeScale time scale}.
  231.      * @param field field utilized by default
  232.      * @param year year number (may be 0 or negative for BC years)
  233.      * @param month month number from 1 to 12
  234.      * @param day day number from 1 to 31
  235.      * @param hour hour number from 0 to 23
  236.      * @param minute minute number from 0 to 59
  237.      * @param second second number from 0.0 to 60.0 (excluded)
  238.      * @param timeScale time scale
  239.      * @exception IllegalArgumentException if inconsistent arguments
  240.      * are given (parameters out of range)
  241.      */
  242.     public FieldAbsoluteDate(final Field<T> field, final int year, final int month, final int day,
  243.                              final int hour, final int minute, final double second,
  244.                              final TimeScale timeScale) throws IllegalArgumentException {
  245.         this(field, new DateComponents(year, month, day), new TimeComponents(hour, minute, second), timeScale);
  246.     }

  248.     /** Build an instance from a location in a {@link TimeScale time scale}.
  249.      * @param field field utilized by default
  250.      * @param year year number (may be 0 or negative for BC years)
  251.      * @param month month enumerate
  252.      * @param day day number from 1 to 31
  253.      * @param hour hour number from 0 to 23
  254.      * @param minute minute number from 0 to 59
  255.      * @param second second number from 0.0 to 60.0 (excluded)
  256.      * @param timeScale time scale
  257.      * @exception IllegalArgumentException if inconsistent arguments
  258.      * are given (parameters out of range)
  259.      */
  260.     public FieldAbsoluteDate(final Field<T> field, final int year, final Month month, final int day,
  261.                              final int hour, final int minute, final double second,
  262.                              final TimeScale timeScale) throws IllegalArgumentException {
  263.         this(field, new DateComponents(year, month, day), new TimeComponents(hour, minute, second), timeScale);
  264.     }

  266.     /** Build an instance from a location in a {@link TimeScale time scale}.
  267.      * <p>The hour is set to 00:00:00.000.</p>
  268.      * @param field field utilized by default
  269.      * @param date date location in the time scale
  270.      * @param timeScale time scale
  271.      * @exception IllegalArgumentException if inconsistent arguments
  272.      * are given (parameters out of range)
  273.      */
  274.     public FieldAbsoluteDate(final Field<T> field, final DateComponents date, final TimeScale timeScale)
  275.         throws IllegalArgumentException {
  276.         this(field, date, TimeComponents.H00, timeScale);
  277.     }

  279.     /** Build an instance from a location in a {@link TimeScale time scale}.
  280.      * <p>The hour is set to 00:00:00.000.</p>
  281.      * @param field field utilized by default
  282.      * @param year year number (may be 0 or negative for BC years)
  283.      * @param month month number from 1 to 12
  284.      * @param day day number from 1 to 31
  285.      * @param timeScale time scale
  286.      * @exception IllegalArgumentException if inconsistent arguments
  287.      * are given (parameters out of range)
  288.      */
  289.     public FieldAbsoluteDate(final Field<T> field, final int year, final int month, final int day,
  290.                         final TimeScale timeScale) throws IllegalArgumentException {
  291.         this(field, new DateComponents(year, month, day), TimeComponents.H00, timeScale);
  292.     }

  294.     /** Build an instance from a location in a {@link TimeScale time scale}.
  295.      * <p>The hour is set to 00:00:00.000.</p>
  296.      * @param field field utilized by default
  297.      * @param year year number (may be 0 or negative for BC years)
  298.      * @param month month enumerate
  299.      * @param day day number from 1 to 31
  300.      * @param timeScale time scale
  301.      * @exception IllegalArgumentException if inconsistent arguments
  302.      * are given (parameters out of range)
  303.      */
  304.     public FieldAbsoluteDate(final Field<T> field, final int year, final Month month, final int day,
  305.                         final TimeScale timeScale) throws IllegalArgumentException {
  306.         this(field, new DateComponents(year, month, day), TimeComponents.H00, timeScale);
  307.     }

  309.     /** Build an instance from a location in a {@link TimeScale time scale}.
  310.      * @param field field utilized as default
  311.      * @param location location in the time scale
  312.      * @param timeScale time scale
  313.      */
  314.     public FieldAbsoluteDate(final Field<T> field, final Date location, final TimeScale timeScale) {
  315.         this(field, new DateComponents(DateComponents.JAVA_EPOCH,
  316.                                 (int) (location.getTime() / 86400000l)),
  317.                                 new TimeComponents(0.001 * (location.getTime() % 86400000l)),
  318.              timeScale);
  319.     }


  322.     /** Build an instance from an elapsed duration since to another instant.
  323.      * <p>It is important to note that the elapsed duration is <em>not</em>
  324.      * the difference between two readings on a time scale.
  325.      * @param since start instant of the measured duration
  326.      * @param elapsedDuration physically elapsed duration from the <code>since</code>
  327.      * instant, as measured in a regular time scale
  328.      */
  329.     public FieldAbsoluteDate(final FieldAbsoluteDate<T> since, final double elapsedDuration) {
  330.         this(since.epoch, elapsedDuration, since.offset);
  331.     }


  334.     /** Build an instance from an elapsed duration since to another instant.
  335.      * <p>It is important to note that the elapsed duration is <em>not</em>
  336.      * the difference between two readings on a time scale.
  337.      * @param since start instant of the measured duration
  338.      * @param elapsedDuration physically elapsed duration from the <code>since</code>
  339.      * instant, as measured in a regular time scale
  340.      */
  341.     public FieldAbsoluteDate(final AbsoluteDate since, final T elapsedDuration) {
  342.         this(since.getEpoch(), since.getOffset(), elapsedDuration);
  343.     }

  345.     /** Build an instance from an apparent clock offset with respect to another
  346.      * instant <em>in the perspective of a specific {@link TimeScale time scale}</em>.
  347.      * <p>It is important to note that the apparent clock offset <em>is</em> the
  348.      * difference between two readings on a time scale and <em>not</em> an elapsed
  349.      * duration. As an example, the apparent clock offset between the two instants
  350.      * leading to the readings 2005-12-31T23:59:59 and 2006-01-01T00:00:00 in the
  351.      * {@link UTCScale UTC} time scale is 1 second, but the elapsed duration is 2
  352.      * seconds because a leap second has been introduced at the end of 2005 in this
  353.      * time scale.</p>
  354.      * <p>This constructor is the reverse of the {@link #offsetFrom(FieldAbsoluteDate,
  355.      * TimeScale)} method.</p>
  356.      * @param reference reference instant
  357.      * @param apparentOffset apparent clock offset from the reference instant
  358.      * (difference between two readings in the specified time scale)
  359.      * @param timeScale time scale with respect to which the offset is defined
  360.      * @see #offsetFrom(FieldAbsoluteDate, TimeScale)
  361.      */
  362.     public FieldAbsoluteDate(final FieldAbsoluteDate<T> reference, final double apparentOffset, final TimeScale timeScale) {
  363.         this(reference.field, new DateTimeComponents(reference.getComponents(timeScale), apparentOffset),
  364.              timeScale);
  365.     }

  367.     /** Build an instance from mixed double and field raw components.
  368.      * @param epoch reference epoch in seconds from 2000-01-01T12:00:00 TAI
  369.      * @param tA double part of offset since reference epoch
  370.      * @param tB field part of offset since reference epoch
  371.      * @since 9.3
  372.      */
  373.     private FieldAbsoluteDate(final long epoch, final double tA, final T tB) {
  374.         this.field = tB.getField();
  375.         final T sum = tB.add(tA);
  376.         if (Double.isInfinite(sum.getReal())) {
  377.             this.offset = sum;
  378.             this.epoch  = (sum.getReal() < 0) ? Long.MIN_VALUE : Long.MAX_VALUE;
  379.         } else {
  380.             // compute sum exactly, using Møller-Knuth TwoSum algorithm without branching
  381.             // the following statements must NOT be simplified, they rely on floating point
  382.             // arithmetic properties (rounding and representable numbers)
  383.             // at the end, the EXACT result of addition tA + tB
  384.             // is sum + residual, where sum is the closest representable number to the exact
  385.             // result and residual is the missing part that does not fit in the first number
  386.             final double oPrime   = sum.getReal() - tA;
  387.             final double dPrime   = sum.getReal() - oPrime;
  388.             final double deltaO   = tB.getReal() - oPrime;
  389.             final double deltaD   = tA - dPrime;
  390.             final double residual = deltaO + deltaD;
  391.             final long   dl       = (long) FastMath.floor(sum.getReal());
  392.             this.offset = sum.subtract(dl).add(residual);
  393.             this.epoch  = epoch + dl;
  394.         }
  395.     }

  397.     /** Build an instance from a CCSDS Unsegmented Time Code (CUC).
  398.      * <p>
  399.      * CCSDS Unsegmented Time Code is defined in the blue book:
  400.      * CCSDS Time Code Format (CCSDS 301.0-B-4) published in November 2010
  401.      * </p>
  402.      * <p>
  403.      * If the date to be parsed is formatted using version 3 of the standard
  404.      * (CCSDS 301.0-B-3 published in 2002) or if the extension of the preamble
  405.      * field introduced in version 4 of the standard is not used, then the
  406.      * {@code preambleField2} parameter can be set to 0.
  407.      * </p>
  408.      * @param field field for the components
  409.      * @param preambleField1 first byte of the field specifying the format, often
  410.      * not transmitted in data interfaces, as it is constant for a given data interface
  411.      * @param preambleField2 second byte of the field specifying the format
  412.      * (added in revision 4 of the CCSDS standard in 2010), often not transmitted in data
  413.      * interfaces, as it is constant for a given data interface (value ignored if presence
  414.      * not signaled in {@code preambleField1})
  415.      * @param timeField byte array containing the time code
  416.      * @param agencyDefinedEpoch reference epoch, ignored if the preamble field
  417.      * specifies the {@link #getCCSDSEpoch(Field) CCSDS reference epoch} is used (and hence
  418.      * may be null in this case)
  419.      * @return an instance corresponding to the specified date
  420.      * @param <T> the type of the field elements
  421.      */
  422.     public static <T extends RealFieldElement<T>> FieldAbsoluteDate<T> parseCCSDSUnsegmentedTimeCode(final Field<T> field,
  423.                                                                                                      final byte preambleField1,
  424.                                                                                                      final byte preambleField2,
  425.                                                                                                      final byte[] timeField,
  426.                                                                                                      final FieldAbsoluteDate<T> agencyDefinedEpoch) {

  428.         // time code identification and reference epoch
  429.         final FieldAbsoluteDate<T> epochF;
  430.         switch (preambleField1 & 0x70) {
  431.             case 0x10:
  432.                 // the reference epoch is CCSDS epoch 1958-01-01T00:00:00 TAI
  433.                 epochF = getCCSDSEpoch(field);
  434.                 break;
  435.             case 0x20:
  436.                 // the reference epoch is agency defined
  437.                 if (agencyDefinedEpoch == null) {
  438.                     throw new OrekitException(OrekitMessages.CCSDS_DATE_MISSING_AGENCY_EPOCH);
  439.                 }
  440.                 epochF = agencyDefinedEpoch;
  441.                 break;
  442.             default :
  443.                 throw new OrekitException(OrekitMessages.CCSDS_DATE_INVALID_PREAMBLE_FIELD,
  444.                                           formatByte(preambleField1));
  445.         }

  447.         // time field lengths
  448.         int coarseTimeLength = 1 + ((preambleField1 & 0x0C) >>> 2);
  449.         int fineTimeLength   = preambleField1 & 0x03;

  451.         if ((preambleField1 & 0x80) != 0x0) {
  452.             // there is an additional octet in preamble field
  453.             coarseTimeLength += (preambleField2 & 0x60) >>> 5;
  454.             fineTimeLength   += (preambleField2 & 0x1C) >>> 2;
  455.         }

  457.         if (timeField.length != coarseTimeLength + fineTimeLength) {
  458.             throw new OrekitException(OrekitMessages.CCSDS_DATE_INVALID_LENGTH_TIME_FIELD,
  459.                                       timeField.length, coarseTimeLength + fineTimeLength);
  460.         }

  462.         T seconds = field.getZero();
  463.         for (int i = 0; i < coarseTimeLength; ++i) {
  464.             seconds = seconds.multiply(256).add(field.getZero().add(toUnsigned(timeField[i])));
  465.         }
  466.         T subseconds = field.getZero();
  467.         for (int i = timeField.length - 1; i >= coarseTimeLength; --i) {
  468.             subseconds = (subseconds.add(toUnsigned(timeField[i]))).divide(256);
  469.         }
  470.         return new FieldAbsoluteDate<>(epochF, seconds).shiftedBy(subseconds);

  472.     }

  474.     /** Build an instance from a CCSDS Day Segmented Time Code (CDS).
  475.      * <p>
  476.      * CCSDS Day Segmented Time Code is defined in the blue book:
  477.      * CCSDS Time Code Format (CCSDS 301.0-B-4) published in November 2010
  478.      * </p>
  479.      * @param field field for the components
  480.      * @param preambleField field specifying the format, often not transmitted in
  481.      * data interfaces, as it is constant for a given data interface
  482.      * @param timeField byte array containing the time code
  483.      * @param agencyDefinedEpoch reference epoch, ignored if the preamble field
  484.      * specifies the {@link #getCCSDSEpoch(Field) CCSDS reference epoch} is used (and hence
  485.      * may be null in this case)
  486.      * @return an instance corresponding to the specified date
  487.      * @param <T> the type of the field elements
  488.      */
  489.     public static <T extends RealFieldElement<T>> FieldAbsoluteDate<T> parseCCSDSDaySegmentedTimeCode(final Field<T> field,
  490.                                                                                                       final byte preambleField, final byte[] timeField,
  491.                                                                                                       final DateComponents agencyDefinedEpoch) {

  493.         // time code identification
  494.         if ((preambleField & 0xF0) != 0x40) {
  495.             throw new OrekitException(OrekitMessages.CCSDS_DATE_INVALID_PREAMBLE_FIELD,
  496.                                       formatByte(preambleField));
  497.         }

  499.         // reference epoch
  500.         final DateComponents epochDC;
  501.         if ((preambleField & 0x08) == 0x00) {
  502.             // the reference epoch is CCSDS epoch 1958-01-01T00:00:00 TAI
  503.             epochDC = DateComponents.CCSDS_EPOCH;
  504.         } else {
  505.             // the reference epoch is agency defined
  506.             if (agencyDefinedEpoch == null) {
  507.                 throw new OrekitException(OrekitMessages.CCSDS_DATE_MISSING_AGENCY_EPOCH);
  508.             }
  509.             epochDC = agencyDefinedEpoch;
  510.         }

  512.         // time field lengths
  513.         final int daySegmentLength = ((preambleField & 0x04) == 0x0) ? 2 : 3;
  514.         final int subMillisecondLength = (preambleField & 0x03) << 1;
  515.         if (subMillisecondLength == 6) {
  516.             throw new OrekitException(OrekitMessages.CCSDS_DATE_INVALID_PREAMBLE_FIELD,
  517.                                       formatByte(preambleField));
  518.         }
  519.         if (timeField.length != daySegmentLength + 4 + subMillisecondLength) {
  520.             throw new OrekitException(OrekitMessages.CCSDS_DATE_INVALID_LENGTH_TIME_FIELD,
  521.                                       timeField.length, daySegmentLength + 4 + subMillisecondLength);
  522.         }


  525.         int i   = 0;
  526.         int day = 0;
  527.         while (i < daySegmentLength) {
  528.             day = day * 256 + toUnsigned(timeField[i++]);
  529.         }

  531.         long milliInDay = 0l;
  532.         while (i < daySegmentLength + 4) {
  533.             milliInDay = milliInDay * 256 + toUnsigned(timeField[i++]);
  534.         }
  535.         final int milli   = (int) (milliInDay % 1000l);
  536.         final int seconds = (int) ((milliInDay - milli) / 1000l);

  538.         double subMilli = 0;
  539.         double divisor  = 1;
  540.         while (i < timeField.length) {
  541.             subMilli = subMilli * 256 + toUnsigned(timeField[i++]);
  542.             divisor *= 1000;
  543.         }

  545.         final DateComponents date = new DateComponents(epochDC, day);
  546.         final TimeComponents time = new TimeComponents(seconds);
  547.         return new FieldAbsoluteDate<>(field, date, time, TimeScalesFactory.getUTC()).shiftedBy(milli * 1.0e-3 + subMilli / divisor);

  549.     }

  551.     /** Build an instance from a CCSDS Calendar Segmented Time Code (CCS).
  552.      * <p>
  553.      * CCSDS Calendar Segmented Time Code is defined in the blue book:
  554.      * CCSDS Time Code Format (CCSDS 301.0-B-4) published in November 2010
  555.      * </p>
  556.      * @param preambleField field specifying the format, often not transmitted in
  557.      * data interfaces, as it is constant for a given data interface
  558.      * @param timeField byte array containing the time code
  559.      * @return an instance corresponding to the specified date
  560.      */
  561.     public FieldAbsoluteDate<T> parseCCSDSCalendarSegmentedTimeCode(final byte preambleField, final byte[] timeField) {

  563.         // time code identification
  564.         if ((preambleField & 0xF0) != 0x50) {
  565.             throw new OrekitException(OrekitMessages.CCSDS_DATE_INVALID_PREAMBLE_FIELD,
  566.                                       formatByte(preambleField));
  567.         }

  569.         // time field length
  570.         final int length = 7 + (preambleField & 0x07);
  571.         if (length == 14) {
  572.             throw new OrekitException(OrekitMessages.CCSDS_DATE_INVALID_PREAMBLE_FIELD,
  573.                                       formatByte(preambleField));
  574.         }
  575.         if (timeField.length != length) {
  576.             throw new OrekitException(OrekitMessages.CCSDS_DATE_INVALID_LENGTH_TIME_FIELD,
  577.                                       timeField.length, length);
  578.         }

  580.         // date part in the first four bytes
  581.         final DateComponents date;
  582.         if ((preambleField & 0x08) == 0x00) {
  583.             // month of year and day of month variation
  584.             date = new DateComponents(toUnsigned(timeField[0]) * 256 + toUnsigned(timeField[1]),
  585.                                       toUnsigned(timeField[2]),
  586.                                       toUnsigned(timeField[3]));
  587.         } else {
  588.             // day of year variation
  589.             date = new DateComponents(toUnsigned(timeField[0]) * 256 + toUnsigned(timeField[1]),
  590.                                       toUnsigned(timeField[2]) * 256 + toUnsigned(timeField[3]));
  591.         }

  593.         // time part from bytes 5 to last (between 7 and 13 depending on precision)
  594.         final TimeComponents time = new TimeComponents(toUnsigned(timeField[4]),
  595.                                                        toUnsigned(timeField[5]),
  596.                                                        toUnsigned(timeField[6]));
  597.         double subSecond = 0;
  598.         double divisor   = 1;
  599.         for (int i = 7; i < length; ++i) {
  600.             subSecond = subSecond * 100 + toUnsigned(timeField[i]);
  601.             divisor *= 100;
  602.         }

  604.         return new FieldAbsoluteDate<>(field, date, time, TimeScalesFactory.getUTC()).shiftedBy(subSecond / divisor);

  606.     }

  608.     /** Decode a signed byte as an unsigned int value.
  609.      * @param b byte to decode
  610.      * @return an unsigned int value
  611.      */
  612.     private static int toUnsigned(final byte b) {
  613.         final int i = (int) b;
  614.         return (i < 0) ? 256 + i : i;
  615.     }

  617.     /** Format a byte as an hex string for error messages.
  618.      * @param data byte to format
  619.      * @return a formatted string
  620.      */
  621.     private static String formatByte(final byte data) {
  622.         return "0x" + Integer.toHexString(data).toUpperCase();
  623.     }

  625.     /** Build an instance corresponding to a Julian Day date.
  626.      * @param jd Julian day
  627.      * @param secondsSinceNoon seconds in the Julian day
  628.      * (BEWARE, Julian days start at noon, so 0.0 is noon)
  629.      * @param timeScale time scale in which the seconds in day are defined
  630.      * @return a new instant
  631.      * @param <T> the type of the field elements
  632.      */
  633.     public static <T extends RealFieldElement<T>> FieldAbsoluteDate<T> createJDDate(final int jd, final T secondsSinceNoon,
  634.                                                                                     final TimeScale timeScale) {
  635.         return new FieldAbsoluteDate<>(secondsSinceNoon.getField(), new DateComponents(DateComponents.JULIAN_EPOCH, jd),
  636.                                        TimeComponents.H12, timeScale).shiftedBy(secondsSinceNoon);
  637.     }

  639.     /** Build an instance corresponding to a Modified Julian Day date.
  640.      * @param mjd modified Julian day
  641.      * @param secondsInDay seconds in the day
  642.      * @param timeScale time scale in which the seconds in day are defined
  643.      * @return a new instant
  644.      * @param <T> the type of the field elements
  645.      */
  646.     public static <T extends RealFieldElement<T>> FieldAbsoluteDate<T> createMJDDate(final int mjd, final T secondsInDay,
  647.                                                                                      final TimeScale timeScale) {
  648.         return new FieldAbsoluteDate<>(secondsInDay.getField(),
  649.                                        new DateComponents(DateComponents.MODIFIED_JULIAN_EPOCH, mjd),
  650.                                        TimeComponents.H00,
  651.                                        timeScale).shiftedBy(secondsInDay);
  652.     }

  654.     /** Build an instance corresponding to a GPS date.
  655.      * <p>GPS dates are provided as a week number starting at
  656.      * {@link #getGPSEpoch(Field) GPS epoch} and as a number of milliseconds
  657.      * since week start.</p>
  658.      * @param weekNumber week number since {@link #getGPSEpoch(Field) GPS epoch}
  659.      * @param milliInWeek number of milliseconds since week start
  660.      * @return a new instant
  661.      * @param <T> the type of the field elements
  662.      */
  663.     public static <T extends RealFieldElement<T>> FieldAbsoluteDate<T> createGPSDate(final int weekNumber, final T milliInWeek) {
  664.         final int day = (int) FastMath.floor(milliInWeek.getReal() / (1000.0 * Constants.JULIAN_DAY));
  665.         final T secondsInDay = milliInWeek.divide(1000.0).subtract(day * Constants.JULIAN_DAY);
  666.         return new FieldAbsoluteDate<>(milliInWeek.getField(), new DateComponents(DateComponents.GPS_EPOCH, weekNumber * 7 + day),
  667.                                        TimeComponents.H00, TimeScalesFactory.getGPS()).shiftedBy(secondsInDay);
  668.     }

  670.     /** Build an instance corresponding to a Julian Epoch (JE).
  671.      * <p>According to Lieske paper: <a
  672.      * href="http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?1979A%26A....73..282L&amp;defaultprint=YES&amp;filetype=.pdf.">
  673.      * Precession Matrix Based on IAU (1976) System of Astronomical Constants</a>, Astronomy and Astrophysics,
  674.      * vol. 73, no. 3, Mar. 1979, p. 282-284, Julian Epoch is related to Julian Ephemeris Date as:</p>
  675.      * <pre>
  676.      * JE = 2000.0 + (JED - 2451545.0) / 365.25
  677.      * </pre>
  678.      * <p>
  679.      * This method reverts the formula above and computes an {@code FieldAbsoluteDate<T>} from the Julian Epoch.
  680.      * </p>
  681.      * @param julianEpoch Julian epoch, like 2000.0 for defining the classical reference J2000.0
  682.      * @return a new instant
  683.      * @see #getJ2000Epoch(Field)
  684.      * @see #createBesselianEpoch(RealFieldElement)
  685.      * @param <T> the type of the field elements
  686.      */
  687.     public static <T extends RealFieldElement<T>> FieldAbsoluteDate<T> createJulianEpoch(final T julianEpoch) {
  688.         return new FieldAbsoluteDate<>(getJ2000Epoch(julianEpoch.getField()),
  689.                                        julianEpoch.subtract(2000.0).multiply(Constants.JULIAN_YEAR));
  690.     }

  692.     /** Build an instance corresponding to a Besselian Epoch (BE).
  693.      * <p>According to Lieske paper: <a
  694.      * href="http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?1979A%26A....73..282L&amp;defaultprint=YES&amp;filetype=.pdf.">
  695.      * Precession Matrix Based on IAU (1976) System of Astronomical Constants</a>, Astronomy and Astrophysics,
  696.      * vol. 73, no. 3, Mar. 1979, p. 282-284, Besselian Epoch is related to Julian Ephemeris Date as:</p>
  697.      * <pre>
  698.      * BE = 1900.0 + (JED - 2415020.31352) / 365.242198781
  699.      * </pre>
  700.      * <p>
  701.      * This method reverts the formula above and computes an {@code FieldAbsoluteDate<T>} from the Besselian Epoch.
  702.      * </p>
  703.      * @param besselianEpoch Besselian epoch, like 1950 for defining the classical reference B1950.0
  704.      * @return a new instant
  705.      * @see #createJulianEpoch(RealFieldElement)
  706.      * @param <T> the type of the field elements
  707.      */
  708.     public static <T extends RealFieldElement<T>> FieldAbsoluteDate<T> createBesselianEpoch(final T besselianEpoch) {
  709.         return new FieldAbsoluteDate<>(getJ2000Epoch(besselianEpoch.getField()),
  710.                                        besselianEpoch.subtract(1900).multiply(Constants.BESSELIAN_YEAR).add(
  711.                                        Constants.JULIAN_DAY * (-36525) + Constants.JULIAN_DAY * 0.31352));
  712.     }

  714.     /** Reference epoch for julian dates: -4712-01-01T12:00:00 Terrestrial Time.
  715.      * <p>Both <code>java.util.Date</code> and {@link DateComponents} classes
  716.      * follow the astronomical conventions and consider a year 0 between
  717.      * years -1 and +1, hence this reference date lies in year -4712 and not
  718.      * in year -4713 as can be seen in other documents or programs that obey
  719.      * a different convention (for example the <code>convcal</code> utility).</p>
  720.      * @param field field for the components
  721.      * @return FieldAbsoluteDate<T> FieldAbsoluteDate<T> representing {@link AbsoluteDate#JULIAN_EPOCH}
  722.      * @param <T> the type of the field elements
  723.      */
  724.     public static <T extends RealFieldElement<T>> FieldAbsoluteDate<T> getJulianEpoch(final Field<T> field) {
  725.         return new FieldAbsoluteDate<>(field, AbsoluteDate.JULIAN_EPOCH);
  726.     }

  728.     /** Reference epoch for modified julian dates: 1858-11-17T00:00:00 Terrestrial Time.
  729.      * @param field field for the components
  730.      * @return FieldAbsoluteDate<T> FieldAbsoluteDate<T> representing {@link AbsoluteDate#MODIFIED_JULIAN_EPOCH}
  731.      * @param <T> the type of the field elements
  732.      */
  733.     public static <T extends RealFieldElement<T>> FieldAbsoluteDate<T> getModifiedJulianEpoch(final Field<T> field) {
  734.         return new FieldAbsoluteDate<>(field, AbsoluteDate.MODIFIED_JULIAN_EPOCH);
  735.     }

  737.     /** Reference epoch for 1950 dates: 1950-01-01T00:00:00 Terrestrial Time.
  738.      * @param field field for the components
  739.      * @return FieldAbsoluteDate<T> FieldAbsoluteDate<T> representing {@link AbsoluteDate#FIFTIES_EPOCH}
  740.      * @param <T> the type of the field elements
  741.      */
  742.     public static <T extends RealFieldElement<T>> FieldAbsoluteDate<T> getFiftiesEpoch(final Field<T> field) {
  743.         return new FieldAbsoluteDate<>(field, AbsoluteDate.FIFTIES_EPOCH);
  744.     }
  745.     /** Reference epoch for CCSDS Time Code Format (CCSDS 301.0-B-4):
  746.      * 1958-01-01T00:00:00 International Atomic Time (<em>not</em> UTC).
  747.      * @param field field for the components
  748.      * @return FieldAbsoluteDate<T> FieldAbsoluteDate<T> representing {@link AbsoluteDate#CCSDS_EPOCH}
  749.      * @param <T> the type of the field elements
  750.      */
  751.     public static <T extends RealFieldElement<T>> FieldAbsoluteDate<T> getCCSDSEpoch(final Field<T> field) {
  752.         return new FieldAbsoluteDate<>(field, AbsoluteDate.CCSDS_EPOCH);
  753.     }

  755.     /** Reference epoch for Galileo System Time: 1999-08-22T00:00:00 UTC.
  756.      * @param field field for the components
  757.      * @return FieldAbsoluteDate<T> FieldAbsoluteDate<T> representing {@link AbsoluteDate#GALILEO_EPOCH}
  758.      * @param <T> the type of the field elements
  759.      */
  760.     public static <T extends RealFieldElement<T>> FieldAbsoluteDate<T> getGalileoEpoch(final Field<T> field) {
  761.         return new FieldAbsoluteDate<>(field, AbsoluteDate.GALILEO_EPOCH);
  762.     }

  764.     /** Reference epoch for GPS weeks: 1980-01-06T00:00:00 GPS time.
  765.      * @param field field for the components
  766.      * @return FieldAbsoluteDate<T> FieldAbsoluteDate<T> representing {@link AbsoluteDate#GPS_EPOCH}
  767.      * @param <T> the type of the field elements
  768.      */
  769.     public static <T extends RealFieldElement<T>> FieldAbsoluteDate<T> getGPSEpoch(final Field<T> field) {
  770.         return new FieldAbsoluteDate<>(field, AbsoluteDate.GPS_EPOCH);
  771.     }

  773.     /** J2000.0 Reference epoch: 2000-01-01T12:00:00 Terrestrial Time (<em>not</em> UTC).
  774.      * @param field field for the components
  775.      * @see #createJulianEpoch(RealFieldElement)
  776.      * @see #createBesselianEpoch(RealFieldElement)
  777.      * @return FieldAbsoluteDate<T> FieldAbsoluteDate<T> representing {@link AbsoluteDate#J2000_EPOCH}
  778.      * @param <T> the type of the field elements
  779.      */
  780.     public static <T extends RealFieldElement<T>> FieldAbsoluteDate<T> getJ2000Epoch(final Field<T> field) {
  781.         return new FieldAbsoluteDate<>(field, AbsoluteDate.J2000_EPOCH);
  782.     }

  784.     /** Java Reference epoch: 1970-01-01T00:00:00 Universal Time Coordinate.
  785.      * <p>
  786.      * Between 1968-02-01 and 1972-01-01, UTC-TAI = 4.213 170 0s + (MJD - 39 126) x 0.002 592s.
  787.      * As on 1970-01-01 MJD = 40587, UTC-TAI = 8.000082s
  788.      * </p>
  789.      * @param field field for the components
  790.      * @return FieldAbsoluteDate<T> FieldAbsoluteDate<T> representing {@link AbsoluteDate#JAVA_EPOCH}
  791.      * @param <T> the type of the field elements
  792.      */
  793.     public static <T extends RealFieldElement<T>> FieldAbsoluteDate<T> getJavaEpoch(final Field<T> field) {
  794.         return new FieldAbsoluteDate<>(field, AbsoluteDate.JAVA_EPOCH);
  795.     }

  797.     /** Dummy date at infinity in the past direction.
  798.      * @param field field for the components
  799.      * @return FieldAbsoluteDate<T> FieldAbsoluteDate<T> representing {@link AbsoluteDate#PAST_INFINITY}
  800.      * @param <T> the type of the field elements
  801.      */
  802.     public static <T extends RealFieldElement<T>> FieldAbsoluteDate<T> getPastInfinity(final Field<T> field) {
  803.         return new FieldAbsoluteDate<>(field, AbsoluteDate.PAST_INFINITY);
  804.     }

  806.     /** Dummy date at infinity in the future direction.
  807.      * @param field field for the components
  808.      * @return FieldAbsoluteDate<T> FieldAbsoluteDate<T> representing {@link AbsoluteDate#FUTURE_INFINITY}
  809.      * @param <T> the type of the field elements
  810.      */
  811.     public static <T extends RealFieldElement<T>> FieldAbsoluteDate<T> getFutureInfinity(final Field<T> field) {
  812.         return new FieldAbsoluteDate<>(field, AbsoluteDate.FUTURE_INFINITY);
  813.     }

  815.     /** Get a time-shifted date.
  816.      * <p>
  817.      * Calling this method is equivalent to call {@code new FieldAbsoluteDate&lt;&gt;(this, dt)}.
  818.      * </p>
  819.      * @param dt time shift in seconds
  820.      * @return a new date, shifted with respect to instance (which is immutable)
  821.      * @see org.orekit.utils.PVCoordinates#shiftedBy(double)
  822.      * @see org.orekit.attitudes.Attitude#shiftedBy(double)
  823.      * @see org.orekit.orbits.Orbit#shiftedBy(double)
  824.      * @see org.orekit.propagation.SpacecraftState#shiftedBy(double)
  825.      */
  826.     public FieldAbsoluteDate<T> shiftedBy(final T dt) {
  827.         return new FieldAbsoluteDate<>(this, dt);
  828.     }

  830.     /** Compute the physically elapsed duration between two instants.
  831.      * <p>The returned duration is the number of seconds physically
  832.      * elapsed between the two instants, measured in a regular time
  833.      * scale with respect to surface of the Earth (i.e either the {@link
  834.      * TAIScale TAI scale}, the {@link TTScale TT scale} or the {@link
  835.      * GPSScale GPS scale}). It is the only method that gives a
  836.      * duration with a physical meaning.</p>
  837.      * <p>This method gives the same result (with less computation)
  838.      * as calling {@link #offsetFrom(FieldAbsoluteDate, TimeScale)}
  839.      * with a second argument set to one of the regular scales cited
  840.      * above.</p>
  841.      * <p>This method is the reverse of the {@link #FieldAbsoluteDate(FieldAbsoluteDate,
  842.      * double)} constructor.</p>
  843.      * @param instant instant to subtract from the instance
  844.      * @return offset in seconds between the two instants (positive
  845.      * if the instance is posterior to the argument)
  846.      * @see #offsetFrom(FieldAbsoluteDate, TimeScale)
  847.      * @see #FieldAbsoluteDate(FieldAbsoluteDate, double)
  848.      */
  849.     public T durationFrom(final FieldAbsoluteDate<T> instant) {
  850.         return offset.subtract(instant.offset).add(epoch - instant.epoch);
  851.     }

  853.     /** Compute the physically elapsed duration between two instants.
  854.      * <p>The returned duration is the number of seconds physically
  855.      * elapsed between the two instants, measured in a regular time
  856.      * scale with respect to surface of the Earth (i.e either the {@link
  857.      * TAIScale TAI scale}, the {@link TTScale TT scale} or the {@link
  858.      * GPSScale GPS scale}). It is the only method that gives a
  859.      * duration with a physical meaning.</p>
  860.      * <p>This method gives the same result (with less computation)
  861.      * as calling {@link #offsetFrom(FieldAbsoluteDate, TimeScale)}
  862.      * with a second argument set to one of the regular scales cited
  863.      * above.</p>
  864.      * <p>This method is the reverse of the {@link #FieldAbsoluteDate(FieldAbsoluteDate,
  865.      * double)} constructor.</p>
  866.      * @param instant instant to subtract from the instance
  867.      * @return offset in seconds between the two instants (positive
  868.      * if the instance is posterior to the argument)
  869.      * @see #offsetFrom(FieldAbsoluteDate, TimeScale)
  870.      * @see #FieldAbsoluteDate(FieldAbsoluteDate, double)
  871.      */
  872.     public T durationFrom(final AbsoluteDate instant) {
  873.         return offset.subtract(instant.getOffset()).add(epoch - instant.getEpoch());
  874.     }

  876.     /** Compute the apparent clock offset between two instant <em>in the
  877.      * perspective of a specific {@link TimeScale time scale}</em>.
  878.      * <p>The offset is the number of seconds counted in the given
  879.      * time scale between the locations of the two instants, with
  880.      * all time scale irregularities removed (i.e. considering all
  881.      * days are exactly 86400 seconds long). This method will give
  882.      * a result that may not have a physical meaning if the time scale
  883.      * is irregular. For example since a leap second was introduced at
  884.      * the end of 2005, the apparent offset between 2005-12-31T23:59:59
  885.      * and 2006-01-01T00:00:00 is 1 second, but the physical duration
  886.      * of the corresponding time interval as returned by the {@link
  887.      * #durationFrom(FieldAbsoluteDate)} method is 2 seconds.</p>
  888.      * <p>This method is the reverse of the {@link #FieldAbsoluteDate(FieldAbsoluteDate,
  889.      * double, TimeScale)} constructor.</p>
  890.      * @param instant instant to subtract from the instance
  891.      * @param timeScale time scale with respect to which the offset should
  892.      * be computed
  893.      * @return apparent clock offset in seconds between the two instants
  894.      * (positive if the instance is posterior to the argument)
  895.      * @see #durationFrom(FieldAbsoluteDate)
  896.      * @see #FieldAbsoluteDate(FieldAbsoluteDate, double, TimeScale)
  897.      */
  898.     public T offsetFrom(final FieldAbsoluteDate<T> instant, final TimeScale timeScale) {
  899.         final long   elapsedDurationA = epoch - instant.epoch;
  900.         final T elapsedDurationB = offset.add(timeScale.offsetFromTAI(this)).
  901.                                    subtract(instant.offset.add(timeScale.offsetFromTAI(instant)));
  902.         return  elapsedDurationB.add(elapsedDurationA);
  903.     }

  905.     /** Compute the offset between two time scales at the current instant.
  906.      * <p>The offset is defined as <i>l₁-l₂</i>
  907.      * where <i>l₁</i> is the location of the instant in
  908.      * the <code>scale1</code> time scale and <i>l₂</i> is the
  909.      * location of the instant in the <code>scale2</code> time scale.</p>
  910.      * @param scale1 first time scale
  911.      * @param scale2 second time scale
  912.      * @return offset in seconds between the two time scales at the
  913.      * current instant
  914.      */
  915.     public T timeScalesOffset(final TimeScale scale1, final TimeScale scale2) {
  916.         return scale1.offsetFromTAI(this).subtract(scale2.offsetFromTAI(this));
  917.     }

  919.     /** Convert the instance to a Java {@link java.util.Date Date}.
  920.      * <p>Conversion to the Date class induces a loss of precision because
  921.      * the Date class does not provide sub-millisecond information. Java Dates
  922.      * are considered to be locations in some times scales.</p>
  923.      * @param timeScale time scale to use
  924.      * @return a {@link java.util.Date Date} instance representing the location
  925.      * of the instant in the time scale
  926.      */
  927.     public Date toDate(final TimeScale timeScale) {
  928.         final double time = epoch + (offset.getReal() + timeScale.offsetFromTAI(this).getReal());
  929.         return new Date(FastMath.round((time + 10957.5 * 86400.0) * 1000));
  930.     }

  932.     /** Split the instance into date/time components.
  933.      * @param timeScale time scale to use
  934.      * @return date/time components
  935.      */
  936.     public DateTimeComponents getComponents(final TimeScale timeScale) {

  938.         if (Double.isInfinite(offset.getReal())) {
  939.             // special handling for past and future infinity
  940.             if (offset.getReal() < 0) {
  941.                 return new DateTimeComponents(DateComponents.MIN_EPOCH, TimeComponents.H00);
  942.             } else {
  943.                 return new DateTimeComponents(DateComponents.MAX_EPOCH,
  944.                                               new TimeComponents(23, 59, 59.999));
  945.             }
  946.         }

  948.         // compute offset from 2000-01-01T00:00:00 in specified time scale exactly,
  949.         // using Møller-Knuth TwoSum algorithm without branching
  950.         // the following statements must NOT be simplified, they rely on floating point
  951.         // arithmetic properties (rounding and representable numbers)
  952.         // at the end, the EXACT result of addition offset + timeScale.offsetFromTAI(this)
  953.         // is sum + residual, where sum is the closest representable number to the exact
  954.         // result and residual is the missing part that does not fit in the first number
  955.         final double taiOffset = timeScale.offsetFromTAI(this).getReal();
  956.         final double sum       = offset.getReal() + taiOffset;
  957.         final double oPrime    = sum - taiOffset;
  958.         final double dPrime    = sum - oPrime;
  959.         final double deltaO    = offset.getReal() - oPrime;
  960.         final double deltaD    = taiOffset - dPrime;
  961.         final double residual  = deltaO + deltaD;

  963.         // split date and time
  964.         final long   carry = (long) FastMath.floor(sum);
  965.         double offset2000B = (sum - carry) + residual;
  966.         long   offset2000A = epoch + carry + 43200l;
  967.         if (offset2000B < 0) {
  968.             offset2000A -= 1;
  969.             offset2000B += 1;
  970.         }
  971.         long time = offset2000A % 86400l;
  972.         if (time < 0l) {
  973.             time += 86400l;
  974.         }
  975.         final int date = (int) ((offset2000A - time) / 86400l);

  977.         // extract calendar elements
  978.         final DateComponents dateComponents = new DateComponents(DateComponents.J2000_EPOCH, date);
  979.         TimeComponents timeComponents = new TimeComponents((int) time, offset2000B);

  981.         if (timeScale.insideLeap(this)) {
  982.             // fix the seconds number to take the leap into account
  983.             timeComponents = new TimeComponents(timeComponents.getHour(), timeComponents.getMinute(),
  984.                                                 timeComponents.getSecond() + timeScale.getLeap(this).getReal());
  985.         }

  987.         // build the components
  988.         return new DateTimeComponents(dateComponents, timeComponents);

  990.     }

  992.     /** Split the instance into date/time components for a local time.
  993.      * @param minutesFromUTC offset in <em>minutes</em> from UTC (positive Eastwards UTC,
  994.      * negative Westward UTC)
  995.      * @return date/time components
  996.      */
  997.     public DateTimeComponents getComponents(final int minutesFromUTC) {

  999.         final DateTimeComponents utcComponents = getComponents(TimeScalesFactory.getUTC());

  1001.         // shift the date according to UTC offset, but WITHOUT touching the seconds,
  1002.         // as they may exceed 60.0 during a leap seconds introduction,
  1003.         // and we want to preserve these special cases
  1004.         final double seconds = utcComponents.getTime().getSecond();
  1005.         int minute = utcComponents.getTime().getMinute() + minutesFromUTC;
  1006.         final int hourShift;
  1007.         if (minute < 0) {
  1008.             hourShift = (minute - 59) / 60;
  1009.         } else if (minute > 59) {
  1010.             hourShift = minute / 60;
  1011.         } else {
  1012.             hourShift = 0;
  1013.         }
  1014.         minute -= 60 * hourShift;
  1015.         int hour = utcComponents.getTime().getHour() + hourShift;
  1016.         final int dayShift;
  1017.         if (hour < 0) {
  1018.             dayShift = (hour - 23) / 24;
  1019.         } else if (hour > 23) {
  1020.             dayShift = hour / 24;
  1021.         } else {
  1022.             dayShift = 0;
  1023.         }
  1024.         hour -= 24 * dayShift;

  1026.         return new DateTimeComponents(new DateComponents(utcComponents.getDate(), dayShift),
  1027.                                       new TimeComponents(hour, minute, seconds, minutesFromUTC));

  1029.     }

  1031.     /** {@inheritDoc} */
  1032.     public FieldAbsoluteDate<T> getDate() {
  1033.         return this;
  1034.     }

  1036.     /** Get the field.
  1037.      * @return field instance.
  1038.      */
  1039.     public Field<T> getField() {
  1040.         return field;
  1041.     }

  1043.     /** Split the instance into date/time components for a time zone.
  1044.      * @param timeZone time zone
  1045.      * @return date/time components
  1046.      */
  1047.     public DateTimeComponents getComponents( final TimeZone timeZone) {
  1048.         final long milliseconds = FastMath.round((offsetFrom(getJavaEpoch(field), TimeScalesFactory.getUTC()).getReal()) * 1000);
  1049.         return getComponents(timeZone.getOffset(milliseconds) / 60000);
  1050.     }

  1052.     /** Compare the instance with another date.
  1053.      * @param date other date to compare the instance to
  1054.      * @return a negative integer, zero, or a positive integer as this date
  1055.      * is before, simultaneous, or after the specified date.
  1056.      */
  1057.     public int compareTo(final FieldAbsoluteDate<T> date) {
  1058.         return Double.compare(durationFrom(date).getReal(), 0.0);
  1059.     }


  1062.     /** Check if the instance represent the same time as another instance.
  1063.      * @param date other date
  1064.      * @return true if the instance and the other date refer to the same instant
  1065.      */
  1066.     @SuppressWarnings("unchecked")
  1067.     public boolean equals(final Object date) {

  1069.         if (date == this) {
  1070.             // first fast check
  1071.             return true;
  1072.         }

  1074.         if ((date != null) && (date instanceof FieldAbsoluteDate)) {
  1075.             return durationFrom((FieldAbsoluteDate<T>) date).getReal() == 0.0;
  1076.         }

  1078.         return false;

  1080.     }

  1082.     /** Get a hashcode for this date.
  1083.      * @return hashcode
  1084.      */
  1085.     public int hashCode() {
  1086.         final long l = Double.doubleToLongBits(durationFrom(AbsoluteDate.J2000_EPOCH).getReal());
  1087.         return (int) (l ^ (l >>> 32));
  1088.     }

  1090.     /** Get a String representation of the instant location in UTC time scale.
  1091.      * @return a string representation of the instance,
  1092.      * in ISO-8601 format with milliseconds accuracy
  1093.      */
  1094.     public String toString() {
  1095.         return toString(TimeScalesFactory.getUTC());
  1096.     }

  1098.     /** Get a String representation of the instant location.
  1099.      * @param timeScale time scale to use
  1100.      * @return a string representation of the instance,
  1101.      * in ISO-8601 format with milliseconds accuracy
  1102.      */
  1103.     public String toString(final TimeScale timeScale) {
  1104.         return getComponents(timeScale).toString(timeScale.minuteDuration(this));
  1105.     }

  1107.     /** Get a String representation of the instant location for a local time.
  1108.      * @param minutesFromUTC offset in <em>minutes</em> from UTC (positive Eastwards UTC,
  1109.      * negative Westward UTC).
  1110.      * @return string representation of the instance,
  1111.      * in ISO-8601 format with milliseconds accuracy
  1112.      */
  1113.     public String toString(final int minutesFromUTC) {
  1114.         final int minuteDuration = TimeScalesFactory.getUTC().minuteDuration(this);
  1115.         return getComponents(minutesFromUTC).toString(minuteDuration);
  1116.     }

  1118.     /** Get a String representation of the instant location for a time zone.
  1119.      * @param timeZone time zone
  1120.      * @return string representation of the instance,
  1121.      * in ISO-8601 format with milliseconds accuracy
  1122.      */
  1123.     public String toString(final TimeZone timeZone) {
  1124.         final int minuteDuration = TimeScalesFactory.getUTC().minuteDuration(this);
  1125.         return getComponents(timeZone).toString(minuteDuration);
  1126.     }

  1128.     /** Get a time-shifted date.
  1129.      * <p>
  1130.      * Calling this method is equivalent to call <code>new AbsoluteDate(this, dt)</code>.
  1131.      * </p>
  1132.      * @param dt time shift in seconds
  1133.      * @return a new date, shifted with respect to instance (which is immutable)
  1134.      * @see org.orekit.utils.PVCoordinates#shiftedBy(double)
  1135.      * @see org.orekit.attitudes.Attitude#shiftedBy(double)
  1136.      * @see org.orekit.orbits.Orbit#shiftedBy(double)
  1137.      * @see org.orekit.propagation.SpacecraftState#shiftedBy(double)
  1138.      */

  1140.     @Override
  1141.     public FieldAbsoluteDate<T> shiftedBy(final double dt) {
  1142.         return new FieldAbsoluteDate<>(this, dt);
  1143.     }


  1146.     /** Transform the FieldAbsoluteDate in an AbsoluteDate.
  1147.      * @return AbsoluteDate of the FieldObject
  1148.      * */
  1149.     public AbsoluteDate toAbsoluteDate() {
  1150.         return new AbsoluteDate(epoch, offset.getReal());
  1151.     }

  1153. }

Created with JaCoCo 0.8.2.201808211720