UTCTAIOffset.java
/* Copyright 2002-2021 CS GROUP
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* 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,
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*/
package org.orekit.time;
import java.io.Serializable;
import org.hipparchus.CalculusFieldElement;
import org.orekit.utils.Constants;
/** Offset between {@link UTCScale UTC} and {@link TAIScale TAI} time scales.
* <p>The {@link UTCScale UTC} and {@link TAIScale TAI} time scales are two
* scales offset with respect to each other. The {@link TAIScale TAI} scale is
* continuous whereas the {@link UTCScale UTC} includes some discontinuity when
* leap seconds are introduced by the <a href="http://www.iers.org/">International
* Earth Rotation Service</a> (IERS).</p>
* <p>This class represents the offset between the two scales that is
* valid between two leap seconds occurrences. It handles both the linear offsets
* used from 1961-01-01 to 1971-12-31 and the constant integer offsets used since
* 1972-01-01.</p>
* @author Luc Maisonobe
* @see UTCScale
* @see UTCTAIHistoryFilesLoader
*/
public class UTCTAIOffset implements TimeStamped, Serializable {
/** Serializable UID. */
private static final long serialVersionUID = 4742190573136348054L;
/** Leap date. */
private final AbsoluteDate leapDate;
/** Leap date in Modified Julian Day. */
private final int leapDateMJD;
/** Offset start of validity date. */
private final AbsoluteDate validityStart;
/** Reference date for the slope multiplication as Modified Julian Day. */
private final int mjdRef;
/** Reference date for the slope multiplication. */
private final AbsoluteDate reference;
/** Value of the leap at offset validity start (in seconds). */
private final double leap;
/** Offset at validity start in seconds (TAI minus UTC). */
private final double offset;
/** Offset slope in seconds per UTC second (TAI minus UTC / dUTC). */
private final double slopeUTC;
/** Offset slope in seconds per TAI second (TAI minus UTC / dTAI). */
private final double slopeTAI;
/** Simple constructor for a linear model.
* @param leapDate leap date
* @param leapDateMJD leap date in Modified Julian Day
* @param leap value of the leap at offset validity start (in seconds)
* @param offset offset in seconds (TAI minus UTC)
* @param mjdRef reference date for the slope multiplication as Modified Julian Day
* @param slope offset slope in seconds per UTC second (TAI minus UTC / dUTC)
* @param reference date for slope computations.
*/
UTCTAIOffset(final AbsoluteDate leapDate, final int leapDateMJD,
final double leap, final double offset,
final int mjdRef, final double slope, final AbsoluteDate reference) {
this.leapDate = leapDate;
this.leapDateMJD = leapDateMJD;
this.validityStart = leapDate.shiftedBy(leap);
this.mjdRef = mjdRef;
this.reference = reference;
this.leap = leap;
this.offset = offset;
this.slopeUTC = slope;
this.slopeTAI = slope / (1 + slope);
}
/** Get the date of the start of the leap.
* @return date of the start of the leap
* @see #getValidityStart()
*/
public AbsoluteDate getDate() {
return leapDate;
}
/** Get the date of the start of the leap as Modified Julian Day.
* @return date of the start of the leap as Modified Julian Day
*/
public int getMJD() {
return leapDateMJD;
}
/** Get the start time of validity for this offset.
* <p>The start of the validity of the offset is {@link #getLeap()}
* seconds after the start of the leap itself.</p>
* @return start of validity date
* @see #getDate()
*/
public AbsoluteDate getValidityStart() {
return validityStart;
}
/** Get the value of the leap at offset validity start (in seconds).
* @return value of the leap at offset validity start (in seconds)
*/
public double getLeap() {
return leap;
}
/** Get the TAI - UTC offset in seconds.
* @param date date at which the offset is requested
* @return TAI - UTC offset in seconds.
*/
public double getOffset(final AbsoluteDate date) {
if (slopeTAI == 0) {
// we use an if statement here so the offset computation returns
// a finite value when date is AbsoluteDate.FUTURE_INFINITY
// without this if statement, the multiplication between an
// infinite duration and a zero slope would induce a NaN offset
return offset;
} else {
return offset + date.durationFrom(reference) * slopeTAI;
}
}
/** Get the TAI - UTC offset in seconds.
* @param date date at which the offset is requested
* @param <T> type of the filed elements
* @return TAI - UTC offset in seconds.
* @since 9.0
*/
public <T extends CalculusFieldElement<T>> T getOffset(final FieldAbsoluteDate<T> date) {
if (slopeTAI == 0) {
// we use an if statement here so the offset computation returns
// a finite value when date is FieldAbsoluteDate.getFutureInfinity(field)
// without this if statement, the multiplication between an
// infinite duration and a zero slope would induce a NaN offset
return date.getField().getZero().add(offset);
} else {
return date.durationFrom(reference).multiply(slopeTAI).add(offset);
}
}
/** Get the TAI - UTC offset in seconds.
* @param date date components (in UTC) at which the offset is requested
* @param time time components (in UTC) at which the offset is requested
* @return TAI - UTC offset in seconds.
*/
public double getOffset(final DateComponents date, final TimeComponents time) {
final int days = date.getMJD() - mjdRef;
final double fraction = time.getSecondsInUTCDay();
return offset + days * (slopeUTC * Constants.JULIAN_DAY) + fraction * slopeUTC;
}
}