UTCScale.java
/* Copyright 2002-2021 CS GROUP
* Licensed to CS GROUP (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.
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package org.orekit.time;
import java.io.Serializable;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Comparator;
import java.util.List;
import org.hipparchus.CalculusFieldElement;
import org.hipparchus.util.FastMath;
import org.orekit.annotation.DefaultDataContext;
import org.orekit.data.DataContext;
import org.orekit.errors.OrekitException;
import org.orekit.errors.OrekitInternalError;
import org.orekit.utils.Constants;
/** Coordinated Universal Time.
* <p>UTC is related to TAI using step adjustments from time to time
* according to IERS (International Earth Rotation Service) rules. Before 1972,
* these adjustments were piecewise linear offsets. Since 1972, these adjustments
* are piecewise constant offsets, which require introduction of leap seconds.</p>
* <p>Leap seconds are always inserted as additional seconds at the last minute
* of the day, pushing the next day forward. Such minutes are therefore more
* than 60 seconds long. In theory, there may be seconds removal instead of seconds
* insertion, but up to now (2010) it has never been used. As an example, when a
* one second leap was introduced at the end of 2005, the UTC time sequence was
* 2005-12-31T23:59:59 UTC, followed by 2005-12-31T23:59:60 UTC, followed by
* 2006-01-01T00:00:00 UTC.</p>
* <p>This is intended to be accessed thanks to {@link TimeScales},
* so there is no public constructor.</p>
* @author Luc Maisonobe
* @see AbsoluteDate
*/
public class UTCScale implements TimeScale {
/** Serializable UID. */
private static final long serialVersionUID = 20150402L;
/** UTC-TAI offsets. */
private UTCTAIOffset[] offsets;
/** Package private constructor for the factory.
* Used to create the prototype instance of this class that is used to
* clone all subsequent instances of {@link UTCScale}. Initializes the offset
* table that is shared among all instances.
* @param tai TAI time scale this UTC time scale references.
* @param offsets UTC-TAI offsets
*/
UTCScale(final TimeScale tai, final Collection<? extends OffsetModel> offsets) {
// copy input so the original list is unmodified
final List<OffsetModel> offsetModels = new ArrayList<>(offsets);
offsetModels.sort(Comparator.comparing(OffsetModel::getStart));
if (offsetModels.get(0).getStart().getYear() > 1968) {
// the pre-1972 linear offsets are missing, add them manually
// excerpt from UTC-TAI.history file:
// 1961 Jan. 1 - 1961 Aug. 1 1.422 818 0s + (MJD - 37 300) x 0.001 296s
// Aug. 1 - 1962 Jan. 1 1.372 818 0s + ""
// 1962 Jan. 1 - 1963 Nov. 1 1.845 858 0s + (MJD - 37 665) x 0.001 123 2s
// 1963 Nov. 1 - 1964 Jan. 1 1.945 858 0s + ""
// 1964 Jan. 1 - April 1 3.240 130 0s + (MJD - 38 761) x 0.001 296s
// April 1 - Sept. 1 3.340 130 0s + ""
// Sept. 1 - 1965 Jan. 1 3.440 130 0s + ""
// 1965 Jan. 1 - March 1 3.540 130 0s + ""
// March 1 - Jul. 1 3.640 130 0s + ""
// Jul. 1 - Sept. 1 3.740 130 0s + ""
// Sept. 1 - 1966 Jan. 1 3.840 130 0s + ""
// 1966 Jan. 1 - 1968 Feb. 1 4.313 170 0s + (MJD - 39 126) x 0.002 592s
// 1968 Feb. 1 - 1972 Jan. 1 4.213 170 0s + ""
offsetModels.add( 0, new OffsetModel(new DateComponents(1961, 1, 1), 37300, 1.4228180, 0.0012960));
offsetModels.add( 1, new OffsetModel(new DateComponents(1961, 8, 1), 37300, 1.3728180, 0.0012960));
offsetModels.add( 2, new OffsetModel(new DateComponents(1962, 1, 1), 37665, 1.8458580, 0.0011232));
offsetModels.add( 3, new OffsetModel(new DateComponents(1963, 11, 1), 37665, 1.9458580, 0.0011232));
offsetModels.add( 4, new OffsetModel(new DateComponents(1964, 1, 1), 38761, 3.2401300, 0.0012960));
offsetModels.add( 5, new OffsetModel(new DateComponents(1964, 4, 1), 38761, 3.3401300, 0.0012960));
offsetModels.add( 6, new OffsetModel(new DateComponents(1964, 9, 1), 38761, 3.4401300, 0.0012960));
offsetModels.add( 7, new OffsetModel(new DateComponents(1965, 1, 1), 38761, 3.5401300, 0.0012960));
offsetModels.add( 8, new OffsetModel(new DateComponents(1965, 3, 1), 38761, 3.6401300, 0.0012960));
offsetModels.add( 9, new OffsetModel(new DateComponents(1965, 7, 1), 38761, 3.7401300, 0.0012960));
offsetModels.add(10, new OffsetModel(new DateComponents(1965, 9, 1), 38761, 3.8401300, 0.0012960));
offsetModels.add(11, new OffsetModel(new DateComponents(1966, 1, 1), 39126, 4.3131700, 0.0025920));
offsetModels.add(12, new OffsetModel(new DateComponents(1968, 2, 1), 39126, 4.2131700, 0.0025920));
}
// create cache
this.offsets = new UTCTAIOffset[offsetModels.size()];
UTCTAIOffset previous = null;
// link the offsets together
for (int i = 0; i < offsetModels.size(); ++i) {
final OffsetModel o = offsetModels.get(i);
final DateComponents date = o.getStart();
final int mjdRef = o.getMJDRef();
final double offset = o.getOffset();
final double slope = o.getSlope();
// start of the leap
final double previousOffset = (previous == null) ? 0.0 : previous.getOffset(date, TimeComponents.H00);
final AbsoluteDate leapStart = new AbsoluteDate(date, tai).shiftedBy(previousOffset);
// end of the leap
final double startOffset = offset + slope * (date.getMJD() - mjdRef);
final AbsoluteDate leapEnd = new AbsoluteDate(date, tai).shiftedBy(startOffset);
// leap computed at leap start and in UTC scale
final double normalizedSlope = slope / Constants.JULIAN_DAY;
final double leap = leapEnd.durationFrom(leapStart) / (1 + normalizedSlope);
final AbsoluteDate reference = AbsoluteDate.createMJDDate(mjdRef, 0, tai)
.shiftedBy(offset);
previous = new UTCTAIOffset(leapStart, date.getMJD(), leap, offset, mjdRef,
normalizedSlope, reference);
this.offsets[i] = previous;
}
}
/**
* Returns the UTC-TAI offsets underlying this UTC scale.
* <p>
* Modifications to the returned list will not affect this UTC scale instance.
* @return new non-null modifiable list of UTC-TAI offsets time-sorted from
* earliest to latest
*/
public List<UTCTAIOffset> getUTCTAIOffsets() {
final List<UTCTAIOffset> offsetList = new ArrayList<>(offsets.length);
for (int i = 0; i < offsets.length; ++i) {
offsetList.add(offsets[i]);
}
return offsetList;
}
/** {@inheritDoc} */
@Override
public double offsetFromTAI(final AbsoluteDate date) {
final int offsetIndex = findOffsetIndex(date);
if (offsetIndex < 0) {
// the date is before the first known leap
return 0;
} else {
return -offsets[offsetIndex].getOffset(date);
}
}
/** {@inheritDoc} */
@Override
public <T extends CalculusFieldElement<T>> T offsetFromTAI(final FieldAbsoluteDate<T> date) {
final int offsetIndex = findOffsetIndex(date.toAbsoluteDate());
if (offsetIndex < 0) {
// the date is before the first known leap
return date.getField().getZero();
} else {
return offsets[offsetIndex].getOffset(date).negate();
}
}
/** {@inheritDoc} */
@Override
public double offsetToTAI(final DateComponents date,
final TimeComponents time) {
// take offset from local time into account, but ignoring seconds,
// so when we parse an hour like 23:59:60.5 during leap seconds introduction,
// we do not jump to next day
final int minuteInDay = time.getHour() * 60 + time.getMinute() - time.getMinutesFromUTC();
final int correction = minuteInDay < 0 ? (minuteInDay - 1439) / 1440 : minuteInDay / 1440;
// find close neighbors, assuming date in TAI, i.e a date earlier than real UTC date
final int mjd = date.getMJD() + correction;
final UTCTAIOffset offset = findOffset(mjd);
if (offset == null) {
// the date is before the first known leap
return 0;
} else {
return offset.getOffset(date, time);
}
}
/** {@inheritDoc} */
public String getName() {
return "UTC";
}
/** {@inheritDoc} */
public String toString() {
return getName();
}
/** Get the date of the first known leap second.
* @return date of the first known leap second
*/
public AbsoluteDate getFirstKnownLeapSecond() {
return offsets[0].getDate();
}
/** Get the date of the last known leap second.
* @return date of the last known leap second
*/
public AbsoluteDate getLastKnownLeapSecond() {
return offsets[offsets.length - 1].getDate();
}
/** {@inheritDoc} */
@Override
public boolean insideLeap(final AbsoluteDate date) {
final int offsetIndex = findOffsetIndex(date);
if (offsetIndex < 0) {
// the date is before the first known leap
return false;
} else {
return date.compareTo(offsets[offsetIndex].getValidityStart()) < 0;
}
}
/** {@inheritDoc} */
@Override
public <T extends CalculusFieldElement<T>> boolean insideLeap(final FieldAbsoluteDate<T> date) {
return insideLeap(date.toAbsoluteDate());
}
/** {@inheritDoc} */
@Override
public int minuteDuration(final AbsoluteDate date) {
final int offsetIndex = findOffsetIndex(date);
final UTCTAIOffset offset;
if (offsetIndex >= 0 &&
date.compareTo(offsets[offsetIndex].getValidityStart()) < 0) {
// the date is during the leap itself
offset = offsets[offsetIndex];
} else if (offsetIndex + 1 < offsets.length &&
offsets[offsetIndex + 1].getDate().durationFrom(date) <= 60.0) {
// the date is after a leap, but it may be just before the next one
// the next leap will start in one minute, it will extend the current minute
offset = offsets[offsetIndex + 1];
} else {
offset = null;
}
if (offset != null) {
// since this method returns an int we can't return the precise duration in
// all cases, but we can bound it. Some leaps are more than 1s. See #694
return 60 + (int) FastMath.ceil(offset.getLeap());
}
// no leap is expected within the next minute
return 60;
}
/** {@inheritDoc} */
@Override
public <T extends CalculusFieldElement<T>> int minuteDuration(final FieldAbsoluteDate<T> date) {
return minuteDuration(date.toAbsoluteDate());
}
/** {@inheritDoc} */
@Override
public double getLeap(final AbsoluteDate date) {
final int offsetIndex = findOffsetIndex(date);
if (offsetIndex < 0) {
// the date is before the first known leap
return 0;
} else {
return offsets[offsetIndex].getLeap();
}
}
/** {@inheritDoc} */
@Override
public <T extends CalculusFieldElement<T>> T getLeap(final FieldAbsoluteDate<T> date) {
return date.getField().getZero().add(getLeap(date.toAbsoluteDate()));
}
/** Find the index of the offset valid at some date.
* @param date date at which offset is requested
* @return index of the offset valid at this date, or -1 if date is before first offset.
*/
private int findOffsetIndex(final AbsoluteDate date) {
int inf = 0;
int sup = offsets.length;
while (sup - inf > 1) {
final int middle = (inf + sup) >>> 1;
if (date.compareTo(offsets[middle].getDate()) < 0) {
sup = middle;
} else {
inf = middle;
}
}
if (sup == offsets.length) {
// the date is after the last known leap second
return offsets.length - 1;
} else if (date.compareTo(offsets[inf].getDate()) < 0) {
// the date is before the first known leap
return -1;
} else {
return inf;
}
}
/** Find the offset valid at some date.
* @param mjd Modified Julian Day of the date at which offset is requested
* @return offset valid at this date, or null if date is before first offset.
*/
private UTCTAIOffset findOffset(final int mjd) {
int inf = 0;
int sup = offsets.length;
while (sup - inf > 1) {
final int middle = (inf + sup) >>> 1;
if (mjd < offsets[middle].getMJD()) {
sup = middle;
} else {
inf = middle;
}
}
if (sup == offsets.length) {
// the date is after the last known leap second
return offsets[offsets.length - 1];
} else if (mjd < offsets[inf].getMJD()) {
// the date is before the first known leap
return null;
} else {
return offsets[inf];
}
}
/** Replace the instance with a data transfer object for serialization.
* @return data transfer object that will be serialized
*/
@DefaultDataContext
private Object writeReplace() {
return new DataTransferObject();
}
/** Internal class used only for serialization. */
@DefaultDataContext
private static class DataTransferObject implements Serializable {
/** Serializable UID. */
private static final long serialVersionUID = 20131209L;
/** Replace the deserialized data transfer object with a {@link UTCScale}.
* @return replacement {@link UTCScale}
*/
private Object readResolve() {
try {
return DataContext.getDefault().getTimeScales().getUTC();
} catch (OrekitException oe) {
throw new OrekitInternalError(oe);
}
}
}
}