GLONASSDate.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.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.orekit.time;
import java.io.Serializable;
import org.hipparchus.util.FastMath;
import org.orekit.annotation.DefaultDataContext;
import org.orekit.data.DataContext;
import org.orekit.propagation.analytical.gnss.data.GNSSConstants;
import org.orekit.utils.Constants;
/**
* Container for date in GLONASS form.
* @author Bryan Cazabonne
* @see AbsoluteDate
* @see "GLONASS Interface Control Document v1.0, 2016"
* @since 10.0
*/
public class GLONASSDate implements Serializable, TimeStamped {
/** Serializable UID. */
private static final long serialVersionUID = 20190131L;
/** Constant for date computation. */
private static final int C1 = 44195;
/** Constant for date computation. */
private static final int C2 = 45290;
/** The number of the current day in a four year interval N<sub>a</sub>. */
private final int na;
/** The number of the current four year interval N<sub>4</sub>. */
private final int n4;
/** Number of seconds since N<sub>a</sub>. */
private final double secInNa;
/** Current Julian date JD0. */
private double jd0;
/** Greenwich Mean Sidereal Time (rad). */
private double gmst;
/** Corresponding date. */
private final transient AbsoluteDate date;
/** Build an instance corresponding to a GLONASS date.
*
* <p>This method uses the {@link DataContext#getDefault() default data context}.
*
* @param na the number of the current day in a four year interval
* @param n4 the number of the current four year interval
* @param secInNa the number of seconds since na start
* @see #GLONASSDate(int, int, double, TimeScale)
*/
@DefaultDataContext
public GLONASSDate(final int na, final int n4, final double secInNa) {
this(na, n4, secInNa, DataContext.getDefault().getTimeScales().getGLONASS());
}
/**
* Build an instance corresponding to a GLONASS date.
*
* @param na the number of the current day in a four year interval
* @param n4 the number of the current four year interval
* @param secInNa the number of seconds since na start
* @param glonass time scale.
* @since 10.1
*/
public GLONASSDate(final int na,
final int n4,
final double secInNa,
final TimeScale glonass) {
this.na = na;
this.n4 = n4;
this.secInNa = secInNa;
// Compute JD0
final int ratio = FastMath.round((float) (na - 3) / (25 + C1 + C2));
this.jd0 = 1461 * (n4 - 1) + na + 2450082.5 - ratio;
// GMST
this.gmst = computeGMST();
this.date = computeDate(glonass);
}
/** Build an instance from an absolute date.
*
* <p>This method uses the {@link DataContext#getDefault() default data context}.
*
* @param date absolute date to consider
* @see #GLONASSDate(AbsoluteDate, TimeScale)
*/
@DefaultDataContext
public GLONASSDate(final AbsoluteDate date) {
this(date, DataContext.getDefault().getTimeScales().getGLONASS());
}
/**
* Build an instance from an absolute date.
*
* @param date absolute date to consider
* @param glonass time scale.
* @since 10.1
*/
public GLONASSDate(final AbsoluteDate date, final TimeScale glonass) {
final DateTimeComponents dateTime = date.getComponents(glonass);
// N4
final int year = dateTime.getDate().getYear();
this.n4 = ((int) (year - 1996) / 4) + 1;
// Na
final int start = 1996 + 4 * (n4 - 1);
final double duration = date.durationFrom(new AbsoluteDate(start, 1, 1, glonass));
this.na = (int) (duration / 86400) + 1;
this.secInNa = dateTime.getTime().getSecondsInLocalDay();
// Compute JD0
final int ratio = FastMath.round((float) (na - 3) / (25 + C1 + C2));
this.jd0 = 1461 * (n4 - 1) + na + 2450082.5 - ratio;
// GMST
this.gmst = computeGMST();
this.date = date;
}
@Override
public AbsoluteDate getDate() {
return date;
}
/** Get the number of seconds since N<sub>a</sub> start.
* @return number of seconds since N<sub>a</sub> start
*/
public double getSecInDay() {
return secInNa;
}
/** Get the number of the current day in a four year interval.
* @return the number of the current day in a four year interval
*/
public int getDayNumber() {
return na;
}
/** Get the number of the current four year interval.
* @return the number of the current four year interval
*/
public int getIntervalNumber() {
return n4;
}
/** Get the current Julian date JD0.
* @return the current date JD0
*/
public double getJD0() {
return jd0;
}
/** Get the Greenwich Mean Sidereal Time.
* @return the Greenwich Mean Sidereal Time (rad)
*/
public double getGMST() {
return gmst;
}
/** Compute the Greenwich Mean Sidereal Time using the current Julian date JD0.
* @return the Greenwich Mean Sidereal Time (rad)
*/
private double computeGMST() {
final double ref = 2451545.0;
// Earth's rotation angle in radians
final double era = 2. * GNSSConstants.GLONASS_PI *
(0.7790572732640 + 1.00273781191135448 * (jd0 - ref));
// Time from Epoch 2000 (1st January, 00:00 UTC) till current Epoch in Julian centuries
final double time = (jd0 - ref) / Constants.JULIAN_CENTURY;
// Time to the power n
final double time2 = time * time;
final double time3 = time2 * time;
final double time4 = time2 * time2;
final double time5 = time2 * time3;
// GMST computation
final double gTime = era + 7.03270726e-8 + time * 2.23603658710194e-2 +
time2 * 6.7465784654e-6 - time3 * 2.1332e-12 - time4 * 1.452308e-10 - time5 * 1.784e-13;
return gTime;
}
/** Compute the GLONASS date.
* @return the date
* @param glonass time scale.
*/
private AbsoluteDate computeDate(final TimeScale glonass) {
// Compute the number of Julian day for the current date
final double jdn = jd0 + 0.5;
// Coefficients
final int a = (int) (jdn + 32044);
final int b = (4 * a + 3) / 146097;
final int c = a - (146097 * b) / 4;
final int d = (4 * c + 3) / 1461;
final int e = c - (1461 * d) / 4;
final int m = (5 * e + 2) / 153;
// Year, month and day
final int day = e - (153 * m + 2) / 5 + 1;
final int month = m + 3 - 12 * (m / 10);
final int year = 100 * b + d - 4800 + m / 10;
return new AbsoluteDate(new DateComponents(year, month, day),
new TimeComponents(secInNa),
glonass);
}
/** 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(na, n4, secInNa);
}
/** Internal class used only for serialization. */
@DefaultDataContext
private static class DataTransferObject implements Serializable {
/** Serializable UID. */
private static final long serialVersionUID = 20190131L;
/** The number of the current day in a four year interval N<sub>a</sub>. */
private final int na;
/** The number of the current four year interval N<sub>4</sub>. */
private final int n4;
/** Number of seconds since N<sub>a</sub>. */
private final double secInNa;
/** Simple constructor.
* @param na the number of the current day in a four year interval
* @param n4 the number of the current four year interval
* @param secInNa the number of seconds since na start
*/
DataTransferObject(final int na, final int n4, final double secInNa) {
this.na = na;
this.n4 = n4;
this.secInNa = secInNa;
}
/** Replace the deserialized data transfer object with a {@link GPSDate}.
* @return replacement {@link GPSDate}
*/
private Object readResolve() {
return new GLONASSDate(na, n4, secInNa);
}
}
}