UTCScale.java
- /* Copyright 2002-2013 CS Systèmes d'Information
- * Licensed to CS Systèmes d'Information (CS) under one or more
- * contributor license agreements. See the NOTICE file distributed with
- * this work for additional information regarding copyright ownership.
- * CS licenses this file to You under the Apache License, Version 2.0
- * (the "License"); you may not use this file except in compliance with
- * the License. You may obtain a copy of the License at
- *
- * http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
- package org.orekit.time;
- import java.io.Serializable;
- import java.util.ArrayList;
- import java.util.List;
- import java.util.Map;
- import java.util.SortedMap;
- import org.orekit.errors.OrekitException;
- import org.orekit.errors.TimeStampedCacheException;
- import org.orekit.utils.Constants;
- import org.orekit.utils.ImmutableTimeStampedCache;
- import org.orekit.utils.TimeStampedCache;
- /** 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>The OREKIT library retrieves the post-1972 constant time steps data thanks
- * to the {@link org.orekit.data.DataProvidersManager DataProvidersManager} class.
- * The linear models used between 1961 and 1972 are built-in in the class itself.</p>
- * <p>This is intended to be accessed thanks to the {@link TimeScalesFactory} class,
- * so there is no public constructor. Every call to {@link TimeScalesFactory#getUTC()}
- * will create a new {@link UTCScale} instance, sharing the UTC-TAI offset table between
- * all instances.</p>
- * @author Luc Maisonobe
- * @see AbsoluteDate
- */
- public class UTCScale implements TimeScale {
- /** Serializable UID. */
- private static final long serialVersionUID = 20131209L;
- /** Time steps. */
- private transient TimeStampedCache<UTCTAIOffset> cache;
- /** 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 entries user supplied entries
- * @exception OrekitException if cache cannot be set up
- */
- UTCScale(final SortedMap<DateComponents, Integer> entries) throws OrekitException {
- // create cache
- final List<UTCTAIOffset> data = new Generator(entries).getOffsets();
- cache = new ImmutableTimeStampedCache<UTCTAIOffset>(2, data);
- }
- /** Generator for leap seconds entries. */
- private static class Generator {
- /** List of {@link UTCTAIOffset} entries. */
- private final List<UTCTAIOffset> offsets;
- /** Simple constructor.
- * @param entries user supplied entries
- */
- public Generator(final SortedMap<DateComponents, Integer> entries) {
- offsets = new ArrayList<UTCTAIOffset>();
- // set up the linear offsets used between 1961-01-01 and 1971-12-31
- // 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 + ""
- addOffsetModel(new DateComponents(1961, 1, 1), 37300, 1.4228180, 0.0012960);
- addOffsetModel(new DateComponents(1961, 8, 1), 37300, 1.3728180, 0.0012960);
- addOffsetModel(new DateComponents(1962, 1, 1), 37665, 1.8458580, 0.0011232);
- addOffsetModel(new DateComponents(1963, 11, 1), 37665, 1.9458580, 0.0011232);
- addOffsetModel(new DateComponents(1964, 1, 1), 38761, 3.2401300, 0.0012960);
- addOffsetModel(new DateComponents(1964, 4, 1), 38761, 3.3401300, 0.0012960);
- addOffsetModel(new DateComponents(1964, 9, 1), 38761, 3.4401300, 0.0012960);
- addOffsetModel(new DateComponents(1965, 1, 1), 38761, 3.5401300, 0.0012960);
- addOffsetModel(new DateComponents(1965, 3, 1), 38761, 3.6401300, 0.0012960);
- addOffsetModel(new DateComponents(1965, 7, 1), 38761, 3.7401300, 0.0012960);
- addOffsetModel(new DateComponents(1965, 9, 1), 38761, 3.8401300, 0.0012960);
- addOffsetModel(new DateComponents(1966, 1, 1), 39126, 4.3131700, 0.0025920);
- addOffsetModel(new DateComponents(1968, 2, 1), 39126, 4.2131700, 0.0025920);
- // add leap second entries in chronological order
- for (Map.Entry<DateComponents, Integer> entry : entries.entrySet()) {
- addOffsetModel(entry.getKey(), 0, entry.getValue(), 0);
- }
- }
- /** Retrieve the generated offsets.
- *
- * @return the {@link UTCTAIOffset}s.
- */
- public List<UTCTAIOffset> getOffsets() {
- return this.offsets;
- }
- /** Add an offset model.
- * <p>
- * This method <em>must</em> be called in chronological order.
- * </p>
- * @param date date of the constant offset model start
- * @param mjdRef reference date of the linear model as a modified julian day
- * @param offset offset at reference date in seconds (TAI minus UTC)
- * @param slope offset slope in seconds per UTC day (TAI minus UTC / dUTC)
- */
- private void addOffsetModel(final DateComponents date, final int mjdRef,
- final double offset, final double slope) {
- final TimeScale tai = TimeScalesFactory.getTAI();
- // start of the leap
- final UTCTAIOffset previous = offsets.isEmpty() ? null : offsets.get(offsets.size() - 1);
- 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);
- if (previous != null) {
- previous.setValidityEnd(leapStart);
- }
- offsets.add(new UTCTAIOffset(leapStart, date.getMJD(), leap, offset, mjdRef, normalizedSlope));
- }
- }
- /** {@inheritDoc} */
- public double offsetFromTAI(final AbsoluteDate date) {
- if (cache.getEarliest().getDate().compareTo(date) > 0) {
- // the date is before the first known leap
- return 0;
- } else if (cache.getLatest().getDate().compareTo(date) < 0) {
- // the date is after the last known leap
- return -cache.getLatest().getOffset(date);
- } else {
- // the date is nominally bracketed by two leaps
- try {
- return -cache.getNeighbors(date).get(0).getOffset(date);
- } catch (TimeStampedCacheException tce) {
- // this should never happen as boundaries have been handled in the previous statements
- throw OrekitException.createInternalError(tce);
- }
- }
- }
- /** {@inheritDoc} */
- public double offsetToTAI(final DateComponents date,
- final TimeComponents time) {
- if (cache.getEarliest().getMJD() > date.getMJD()) {
- // the date is before the first known leap
- return 0;
- } else if (cache.getLatest().getMJD() <= date.getMJD()) {
- // the date is after the last known leap
- return cache.getLatest().getOffset(date, time);
- } else {
- // the date is nominally bracketed by two leaps
- try {
- // find close neighbors, assuming date in TAI, i.e a date earlier than real UTC date
- final List<UTCTAIOffset> neighbors =
- cache.getNeighbors(new AbsoluteDate(date, time, TimeScalesFactory.getTAI()));
- if (neighbors.get(1).getMJD() <= date.getMJD()) {
- // the date is in fact just after a leap second!
- return neighbors.get(1).getOffset(date, time);
- } else {
- return neighbors.get(0).getOffset(date, time);
- }
- } catch (TimeStampedCacheException tce) {
- // this should never happen as boundaries have been handled in the previous statements
- throw OrekitException.createInternalError(tce);
- }
- }
- }
- /** {@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 cache.getEarliest().getDate();
- }
- /** Get the date of the last known leap second.
- * @return date of the last known leap second
- */
- public AbsoluteDate getLastKnownLeapSecond() {
- return cache.getLatest().getDate();
- }
- /** Check if date is within a leap second introduction.
- * @param date date to check
- * @return true if time is within a leap second introduction
- */
- public boolean insideLeap(final AbsoluteDate date) {
- if (cache.getEarliest().getDate().compareTo(date) > 0) {
- // the date is before the first known leap
- return false;
- } else if (cache.getLatest().getDate().compareTo(date) < 0) {
- // the date is after the last known leap
- return date.compareTo(cache.getLatest().getValidityStart()) < 0;
- } else {
- // the date is nominally bracketed by two leaps
- try {
- return date.compareTo(cache.getNeighbors(date).get(0).getValidityStart()) < 0;
- } catch (TimeStampedCacheException tce) {
- // this should never happen as boundaries have been handled in the previous statements
- throw OrekitException.createInternalError(tce);
- }
- }
- }
- /** Get the value of the previous leap.
- * @param date date to check
- * @return value of the previous leap
- */
- public double getLeap(final AbsoluteDate date) {
- if (cache.getEarliest().getDate().compareTo(date) > 0) {
- return 0;
- } else if (cache.getLatest().getDate().compareTo(date) < 0) {
- // the date is after the last known leap
- return cache.getLatest().getLeap();
- } else {
- // the date is nominally bracketed by two leaps
- try {
- return cache.getNeighbors(date).get(0).getLeap();
- } catch (TimeStampedCacheException tce) {
- // this should never happen as boundaries have been handled in the previous statements
- throw OrekitException.createInternalError(tce);
- }
- }
- }
- /** Replace the instance with a data transfer object for serialization.
- * <p>
- * This intermediate class serializes only the frame key.
- * </p>
- * @return data transfer object that will be serialized
- */
- private Object writeReplace() {
- return new DataTransferObject();
- }
- /** Internal class used only for serialization. */
- 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 TimeScalesFactory.getUTC();
- } catch (OrekitException oe) {
- throw OrekitException.createInternalError(oe);
- }
- }
- }
- }