UTCScale.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.io.Serializable;
  20. import java.util.List;

  22. import org.hipparchus.RealFieldElement;
  23. import org.orekit.errors.OrekitException;
  24. import org.orekit.errors.OrekitInternalError;
  25. import org.orekit.utils.Constants;

  27. /** Coordinated Universal Time.
  28.  * <p>UTC is related to TAI using step adjustments from time to time
  29.  * according to IERS (International Earth Rotation Service) rules. Before 1972,
  30.  * these adjustments were piecewise linear offsets. Since 1972, these adjustments
  31.  * are piecewise constant offsets, which require introduction of leap seconds.</p>
  32.  * <p>Leap seconds are always inserted as additional seconds at the last minute
  33.  * of the day, pushing the next day forward. Such minutes are therefore more
  34.  * than 60 seconds long. In theory, there may be seconds removal instead of seconds
  35.  * insertion, but up to now (2010) it has never been used. As an example, when a
  36.  * one second leap was introduced at the end of 2005, the UTC time sequence was
  37.  * 2005-12-31T23:59:59 UTC, followed by 2005-12-31T23:59:60 UTC, followed by
  38.  * 2006-01-01T00:00:00 UTC.</p>
  39.  * <p>This is intended to be accessed thanks to the {@link TimeScalesFactory} class,
  40.  * so there is no public constructor.</p>
  41.  * @author Luc Maisonobe
  42.  * @see AbsoluteDate
  43.  */
  44. public class UTCScale implements TimeScale {

  46.     /** Serializable UID. */
  47.     private static final long serialVersionUID = 20150402L;

  49.     /** UTC-TAI offsets. */
  50.     private UTCTAIOffset[] offsets;

  52.     /** Package private constructor for the factory.
  53.      * Used to create the prototype instance of this class that is used to
  54.      * clone all subsequent instances of {@link UTCScale}. Initializes the offset
  55.      * table that is shared among all instances.
  56.      * @param offsetModels UTC-TAI offsets
  57.      */
  58.     UTCScale(final List<OffsetModel> offsetModels) {

  60.         if (offsetModels.get(0).getStart().getYear() > 1968) {
  61.             // the pre-1972 linear offsets are missing, add them manually
  62.             // excerpt from UTC-TAI.history file:
  63.             //  1961  Jan.  1 - 1961  Aug.  1     1.422 818 0s + (MJD - 37 300) x 0.001 296s
  64.             //        Aug.  1 - 1962  Jan.  1     1.372 818 0s +        ""
  65.             //  1962  Jan.  1 - 1963  Nov.  1     1.845 858 0s + (MJD - 37 665) x 0.001 123 2s
  66.             //  1963  Nov.  1 - 1964  Jan.  1     1.945 858 0s +        ""
  67.             //  1964  Jan.  1 -       April 1     3.240 130 0s + (MJD - 38 761) x 0.001 296s
  68.             //        April 1 -       Sept. 1     3.340 130 0s +        ""
  69.             //        Sept. 1 - 1965  Jan.  1     3.440 130 0s +        ""
  70.             //  1965  Jan.  1 -       March 1     3.540 130 0s +        ""
  71.             //        March 1 -       Jul.  1     3.640 130 0s +        ""
  72.             //        Jul.  1 -       Sept. 1     3.740 130 0s +        ""
  73.             //        Sept. 1 - 1966  Jan.  1     3.840 130 0s +        ""
  74.             //  1966  Jan.  1 - 1968  Feb.  1     4.313 170 0s + (MJD - 39 126) x 0.002 592s
  75.             //  1968  Feb.  1 - 1972  Jan.  1     4.213 170 0s +        ""
  76.             offsetModels.add( 0, new OffsetModel(new DateComponents(1961,  1, 1), 37300, 1.4228180, 0.0012960));
  77.             offsetModels.add( 1, new OffsetModel(new DateComponents(1961,  8, 1), 37300, 1.3728180, 0.0012960));
  78.             offsetModels.add( 2, new OffsetModel(new DateComponents(1962,  1, 1), 37665, 1.8458580, 0.0011232));
  79.             offsetModels.add( 3, new OffsetModel(new DateComponents(1963, 11, 1), 37665, 1.9458580, 0.0011232));
  80.             offsetModels.add( 4, new OffsetModel(new DateComponents(1964,  1, 1), 38761, 3.2401300, 0.0012960));
  81.             offsetModels.add( 5, new OffsetModel(new DateComponents(1964,  4, 1), 38761, 3.3401300, 0.0012960));
  82.             offsetModels.add( 6, new OffsetModel(new DateComponents(1964,  9, 1), 38761, 3.4401300, 0.0012960));
  83.             offsetModels.add( 7, new OffsetModel(new DateComponents(1965,  1, 1), 38761, 3.5401300, 0.0012960));
  84.             offsetModels.add( 8, new OffsetModel(new DateComponents(1965,  3, 1), 38761, 3.6401300, 0.0012960));
  85.             offsetModels.add( 9, new OffsetModel(new DateComponents(1965,  7, 1), 38761, 3.7401300, 0.0012960));
  86.             offsetModels.add(10, new OffsetModel(new DateComponents(1965,  9, 1), 38761, 3.8401300, 0.0012960));
  87.             offsetModels.add(11, new OffsetModel(new DateComponents(1966,  1, 1), 39126, 4.3131700, 0.0025920));
  88.             offsetModels.add(12, new OffsetModel(new DateComponents(1968,  2, 1), 39126, 4.2131700, 0.0025920));
  89.         }

  91.         // create cache
  92.         offsets = new UTCTAIOffset[offsetModels.size()];

  94.         UTCTAIOffset previous = null;

  96.         // link the offsets together
  97.         final TimeScale tai = TimeScalesFactory.getTAI();
  98.         for (int i = 0; i < offsetModels.size(); ++i) {

  100.             final OffsetModel    o      = offsetModels.get(i);
  101.             final DateComponents date   = o.getStart();
  102.             final int            mjdRef = o.getMJDRef();
  103.             final double         offset = o.getOffset();
  104.             final double         slope  = o.getSlope();

  106.             // start of the leap
  107.             final double previousOffset    = (previous == null) ? 0.0 : previous.getOffset(date, TimeComponents.H00);
  108.             final AbsoluteDate leapStart   = new AbsoluteDate(date, tai).shiftedBy(previousOffset);

  110.             // end of the leap
  111.             final double startOffset       = offset + slope * (date.getMJD() - mjdRef);
  112.             final AbsoluteDate leapEnd     = new AbsoluteDate(date, tai).shiftedBy(startOffset);

  114.             // leap computed at leap start and in UTC scale
  115.             final double normalizedSlope   = slope / Constants.JULIAN_DAY;
  116.             final double leap              = leapEnd.durationFrom(leapStart) / (1 + normalizedSlope);

  118.             previous = new UTCTAIOffset(leapStart, date.getMJD(), leap, offset, mjdRef, normalizedSlope);
  119.             offsets[i] = previous;

  121.         }

  123.     }

  125.     /** {@inheritDoc} */
  126.     @Override
  127.     public double offsetFromTAI(final AbsoluteDate date) {
  128.         final int offsetIndex = findOffsetIndex(date);
  129.         if (offsetIndex < 0) {
  130.             // the date is before the first known leap
  131.             return 0;
  132.         } else {
  133.             return -offsets[offsetIndex].getOffset(date);
  134.         }
  135.     }

  137.     /** {@inheritDoc} */
  138.     @Override
  139.     public <T extends RealFieldElement<T>> T offsetFromTAI(final FieldAbsoluteDate<T> date) {
  140.         final int offsetIndex = findOffsetIndex(date.toAbsoluteDate());
  141.         if (offsetIndex < 0) {
  142.             // the date is before the first known leap
  143.             return date.getField().getZero();
  144.         } else {
  145.             return offsets[offsetIndex].getOffset(date).negate();
  146.         }
  147.     }

  149.     /** {@inheritDoc} */
  150.     @Override
  151.     public double offsetToTAI(final DateComponents date,
  152.                               final TimeComponents time) {

  154.         // take offset from local time into account, but ignoring seconds,
  155.         // so when we parse an hour like 23:59:60.5 during leap seconds introduction,
  156.         // we do not jump to next day
  157.         final int minuteInDay = time.getHour() * 60 + time.getMinute() - time.getMinutesFromUTC();
  158.         final int correction  = minuteInDay < 0 ? (minuteInDay - 1439) / 1440 : minuteInDay / 1440;

  160.         // find close neighbors, assuming date in TAI, i.e a date earlier than real UTC date
  161.         final int mjd = date.getMJD() + correction;
  162.         final UTCTAIOffset offset = findOffset(mjd);
  163.         if (offset == null) {
  164.             // the date is before the first known leap
  165.             return 0;
  166.         } else {
  167.             return offset.getOffset(date, time);
  168.         }

  170.     }

  172.     /** {@inheritDoc} */
  173.     public String getName() {
  174.         return "UTC";
  175.     }

  177.     /** {@inheritDoc} */
  178.     public String toString() {
  179.         return getName();
  180.     }

  182.     /** Get the date of the first known leap second.
  183.      * @return date of the first known leap second
  184.      */
  185.     public AbsoluteDate getFirstKnownLeapSecond() {
  186.         return offsets[0].getDate();
  187.     }

  189.     /** Get the date of the last known leap second.
  190.      * @return date of the last known leap second
  191.      */
  192.     public AbsoluteDate getLastKnownLeapSecond() {
  193.         return offsets[offsets.length - 1].getDate();
  194.     }

  196.     /** {@inheritDoc} */
  197.     @Override
  198.     public boolean insideLeap(final AbsoluteDate date) {
  199.         final int offsetIndex = findOffsetIndex(date);
  200.         if (offsetIndex < 0) {
  201.             // the date is before the first known leap
  202.             return false;
  203.         } else {
  204.             return date.compareTo(offsets[offsetIndex].getValidityStart()) < 0;
  205.         }
  206.     }

  208.     /** {@inheritDoc} */
  209.     @Override
  210.     public <T extends RealFieldElement<T>> boolean insideLeap(final FieldAbsoluteDate<T> date) {
  211.         return insideLeap(date.toAbsoluteDate());
  212.     }

  214.     /** {@inheritDoc} */
  215.     @Override
  216.     public int minuteDuration(final AbsoluteDate date) {
  217.         final int offsetIndex = findOffsetIndex(date);
  218.         if (offsetIndex < 0) {
  219.             // the date is before the first known leap
  220.             return 60;
  221.         } else {
  222.             if (date.compareTo(offsets[offsetIndex].getValidityStart()) < 0) {
  223.                 // the date is during the leap itself
  224.                 return 61;
  225.             } else {
  226.                 // the date is after a leap, but it may be just before the next one
  227.                 if (offsetIndex + 1 < offsets.length &&
  228.                     offsets[offsetIndex + 1].getDate().durationFrom(date) <= 60.0) {
  229.                     // the next leap will start in one minute, it will extend the current minute
  230.                     return 61;
  231.                 } else {
  232.                     // no leap is expected within the next minute
  233.                     return 60;
  234.                 }
  235.             }
  236.         }
  237.     }

  239.     /** {@inheritDoc} */
  240.     @Override
  241.     public <T extends RealFieldElement<T>> int minuteDuration(final FieldAbsoluteDate<T> date) {
  242.         return minuteDuration(date.toAbsoluteDate());
  243.     }

  245.     /** {@inheritDoc} */
  246.     @Override
  247.     public double getLeap(final AbsoluteDate date) {
  248.         final int offsetIndex = findOffsetIndex(date);
  249.         if (offsetIndex < 0) {
  250.             // the date is before the first known leap
  251.             return 0;
  252.         } else {
  253.             return offsets[offsetIndex].getLeap();
  254.         }
  255.     }

  257.     /** {@inheritDoc} */
  258.     @Override
  259.     public <T extends RealFieldElement<T>> T getLeap(final FieldAbsoluteDate<T> date) {
  260.         return date.getField().getZero().add(getLeap(date.toAbsoluteDate()));
  261.     }

  263.     /** Find the index of the offset valid at some date.
  264.      * @param date date at which offset is requested
  265.      * @return index of the offset valid at this date, or -1 if date is before first offset.
  266.      */
  267.     private int findOffsetIndex(final AbsoluteDate date) {
  268.         int inf = 0;
  269.         int sup = offsets.length;
  270.         while (sup - inf > 1) {
  271.             final int middle = (inf + sup) >>> 1;
  272.             if (date.compareTo(offsets[middle].getDate()) < 0) {
  273.                 sup = middle;
  274.             } else {
  275.                 inf = middle;
  276.             }
  277.         }
  278.         if (sup == offsets.length) {
  279.             // the date is after the last known leap second
  280.             return offsets.length - 1;
  281.         } else if (date.compareTo(offsets[inf].getDate()) < 0) {
  282.             // the date is before the first known leap
  283.             return -1;
  284.         } else {
  285.             return inf;
  286.         }
  287.     }

  289.     /** Find the offset valid at some date.
  290.      * @param mjd Modified Julian Day of the date at which offset is requested
  291.      * @return offset valid at this date, or null if date is before first offset.
  292.      */
  293.     private UTCTAIOffset findOffset(final int mjd) {
  294.         int inf = 0;
  295.         int sup = offsets.length;
  296.         while (sup - inf > 1) {
  297.             final int middle = (inf + sup) >>> 1;
  298.             if (mjd < offsets[middle].getMJD()) {
  299.                 sup = middle;
  300.             } else {
  301.                 inf = middle;
  302.             }
  303.         }
  304.         if (sup == offsets.length) {
  305.             // the date is after the last known leap second
  306.             return offsets[offsets.length - 1];
  307.         } else if (mjd < offsets[inf].getMJD()) {
  308.             // the date is before the first known leap
  309.             return null;
  310.         } else {
  311.             return offsets[inf];
  312.         }
  313.     }

  315.     /** Replace the instance with a data transfer object for serialization.
  316.      * @return data transfer object that will be serialized
  317.      */
  318.     private Object writeReplace() {
  319.         return new DataTransferObject();
  320.     }

  322.     /** Internal class used only for serialization. */
  323.     private static class DataTransferObject implements Serializable {

  325.         /** Serializable UID. */
  326.         private static final long serialVersionUID = 20131209L;

  328.         /** Replace the deserialized data transfer object with a {@link UTCScale}.
  329.          * @return replacement {@link UTCScale}
  330.          */
  331.         private Object readResolve() {
  332.             try {
  333.                 return TimeScalesFactory.getUTC();
  334.             } catch (OrekitException oe) {
  335.                 throw new OrekitInternalError(oe);
  336.             }
  337.         }

  339.     }

  341. }
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