GNSSDate.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 java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.concurrent.atomic.AtomicReference;
import org.hipparchus.util.FastMath;
import org.orekit.annotation.DefaultDataContext;
import org.orekit.data.DataContext;
import org.orekit.errors.OrekitException;
import org.orekit.errors.OrekitMessages;
import org.orekit.frames.EOPEntry;
import org.orekit.gnss.SatelliteSystem;
import org.orekit.utils.Constants;
import org.orekit.utils.IERSConventions;
/** Container for date in GNSS form.
* <p> This class can be used to handle {@link SatelliteSystem#GPS GPS},
* {@link SatelliteSystem#GALILEO Galileo}, {@link SatelliteSystem#BEIDOU BeiDou}
* and {@link SatelliteSystem#QZSS QZSS} dates. </p>
* @author Luc Maisonobe (original code)
* @author Bryan Cazabonne (generalization to all GNSS constellations)
* @see AbsoluteDate
*/
public class GNSSDate implements Serializable, TimeStamped {
/** Serializable UID. */
private static final long serialVersionUID = 201902141L;
/** Duration of a week in days. */
private static final int WEEK_D = 7;
/** Duration of a week in seconds. */
private static final double WEEK_S = WEEK_D * Constants.JULIAN_DAY;
/** Conversion factor from seconds to milliseconds. */
private static final double S_TO_MS = 1000.0;
/** Reference date for ensuring continuity across GNSS week rollover.
* @since 9.3.1
*/
private static AtomicReference<DateComponents> rolloverReference = new AtomicReference<DateComponents>(null);
/** Week number since the GNSS reference epoch. */
private final int weekNumber;
/** Number of milliseconds since week start. */
private final double milliInWeek;
/** Satellite system to consider. */
private final SatelliteSystem system;
/** Corresponding date. */
private final transient AbsoluteDate date;
/** Build an instance corresponding to a GNSS date.
* <p>
* GNSS dates are provided as a week number starting at
* the GNSS reference epoch and as a number of milliseconds
* since week start.
* </p>
* <p>
* Many interfaces provide week number modulo the constellation week cycle. In order to cope with
* this, when the week number is smaller than the week cycle, this constructor assumes a modulo operation
* has been performed and it will fix the week number according to the reference date set up for
* handling rollover (see {@link #setRolloverReference(DateComponents) setRolloverReference(reference)}).
* If the week number is equal to the week cycle or larger, it will be used without any correction.
* </p>
*
* <p>This method uses the {@link DataContext#getDefault() default data context}.
*
* @param weekNumber week number
* @param milliInWeek number of milliseconds since week start
* @param system satellite system to consider
* @see #GNSSDate(int, double, SatelliteSystem, TimeScales)
*/
@DefaultDataContext
public GNSSDate(final int weekNumber, final double milliInWeek,
final SatelliteSystem system) {
this(weekNumber, milliInWeek, system, DataContext.getDefault().getTimeScales());
}
/**
* Build an instance corresponding to a GNSS date.
* <p>
* GNSS dates are provided as a week number starting at the GNSS reference epoch and
* as a number of milliseconds since week start.
* </p>
* <p>
* Many interfaces provide week number modulo the constellation week cycle. In order
* to cope with this, when the week number is smaller than the week cycle, this
* constructor assumes a modulo operation has been performed and it will fix the week
* number according to the reference date set up for handling rollover (see {@link
* #setRolloverReference(DateComponents) setRolloverReference(reference)}). If the
* week number is equal to the week cycle or larger, it will be used without any
* correction.
* </p>
*
* @param weekNumber week number
* @param milliInWeek number of milliseconds since week start
* @param system satellite system to consider
* @param timeScales the set of time scales. Used to retrieve the appropriate time
* scale for the given {@code system}.
* @since 10.1
*/
public GNSSDate(final int weekNumber,
final double milliInWeek,
final SatelliteSystem system,
final TimeScales timeScales) {
final int day = (int) FastMath.floor(milliInWeek / (Constants.JULIAN_DAY * S_TO_MS));
final double secondsInDay = milliInWeek / S_TO_MS - day * Constants.JULIAN_DAY;
int w = weekNumber;
DateComponents dc = new DateComponents(getWeekReferenceDateComponents(system), weekNumber * 7 + day);
final int cycleW = GNSSDateType.getRollOverWeek(system);
if (weekNumber < cycleW) {
DateComponents reference = rolloverReference.get();
if (reference == null) {
// lazy setting of a default reference, using end of EOP entries
final UT1Scale ut1 = timeScales.getUT1(IERSConventions.IERS_2010, true);
final List<EOPEntry> eop = ut1.getEOPHistory().getEntries();
final int lastMJD = eop.get(eop.size() - 1).getMjd();
reference = new DateComponents(DateComponents.MODIFIED_JULIAN_EPOCH, lastMJD);
rolloverReference.compareAndSet(null, reference);
}
// fix GNSS week rollover
final int cycleD = WEEK_D * cycleW;
while (dc.getJ2000Day() < reference.getJ2000Day() - cycleD / 2) {
dc = new DateComponents(dc, cycleD);
w += cycleW;
}
}
this.weekNumber = w;
this.milliInWeek = milliInWeek;
this.system = system;
date = new AbsoluteDate(dc, new TimeComponents(secondsInDay), getTimeScale(system, timeScales));
}
/** Build an instance from an absolute date.
*
* <p>This method uses the {@link DataContext#getDefault() default data context}.
*
* @param date absolute date to consider
* @param system satellite system to consider
* @see #GNSSDate(AbsoluteDate, SatelliteSystem, TimeScales)
*/
@DefaultDataContext
public GNSSDate(final AbsoluteDate date, final SatelliteSystem system) {
this(date, system, DataContext.getDefault().getTimeScales());
}
/**
* Build an instance from an absolute date.
*
* @param date absolute date to consider
* @param system satellite system to consider
* @param timeScales the set of time scales. Used to retrieve the appropriate time
* scale for the given {@code system}.
* @since 10.1
*/
public GNSSDate(final AbsoluteDate date,
final SatelliteSystem system,
final TimeScales timeScales) {
this.system = system;
final AbsoluteDate epoch = getWeekReferenceAbsoluteDate(system, timeScales);
this.weekNumber = (int) FastMath.floor(date.durationFrom(epoch) / WEEK_S);
final AbsoluteDate weekStart = new AbsoluteDate(epoch, WEEK_S * weekNumber);
this.milliInWeek = date.durationFrom(weekStart) * S_TO_MS;
this.date = date;
}
/** Set a reference date for ensuring continuity across GNSS week rollover.
* <p>
* Instance created using the {@link #GNSSDate(int, double, SatelliteSystem) GNSSDate(weekNumber, milliInWeek, system)}
* constructor and with a week number between 0 and the constellation week cycle (cycleW) after this method has been called will
* fix the week number to ensure they correspond to dates between {@code reference - cycleW / 2 weeks}
* and {@code reference + cycleW / 2 weeks}.
* </p>
* <p>
* If this method is never called, a default reference date for rollover will be set using
* the date of the last known EOP entry retrieved from {@link UT1Scale#getEOPHistory() UT1}
* time scale.
* </p>
* @param reference reference date for GNSS week rollover
* @see #getRolloverReference()
* @see #GNSSDate(int, double, SatelliteSystem)
* @since 9.3.1
*/
public static void setRolloverReference(final DateComponents reference) {
rolloverReference.set(reference);
}
/** Get the reference date ensuring continuity across GNSS week rollover.
* @return reference reference date for GNSS week rollover
* @see #setRolloverReference(DateComponents)
* @see #GNSSDate(int, double, SatelliteSystem)
* @since 9.3.1
*/
public static DateComponents getRolloverReference() {
return rolloverReference.get();
}
/** Get the week number since the GNSS reference epoch.
* <p>
* The week number returned here has been fixed for GNSS week rollover, i.e.
* it may be larger than the corresponding week cycle of the constellation.
* </p>
* @return week number since since the GNSS reference epoch
*/
public int getWeekNumber() {
return weekNumber;
}
/** Get the number of milliseconds since week start.
* @return number of milliseconds since week start
*/
public double getMilliInWeek() {
return milliInWeek;
}
/** {@inheritDoc} */
@Override
public AbsoluteDate getDate() {
return date;
}
/** Get the time scale related to the given satellite system.
* @param satellite satellite system
* @param timeScales set of time scales.
* @return the time scale
*/
private TimeScale getTimeScale(final SatelliteSystem satellite,
final TimeScales timeScales) {
switch (satellite) {
case GPS : return timeScales.getGPS();
case GALILEO : return timeScales.getGST();
case QZSS : return timeScales.getQZSS();
case BEIDOU : return timeScales.getBDT();
case IRNSS : return timeScales.getIRNSS();
case SBAS : return timeScales.getGPS();
default : throw new OrekitException(OrekitMessages.INVALID_SATELLITE_SYSTEM, satellite);
}
}
/** Get the reference epoch of the week number for the given satellite system.
* <p> Returned parameter is an AbsoluteDate. </p>
* @param satellite satellite system
* @param timeScales set of time scales.
* @return the reference epoch
*/
private AbsoluteDate getWeekReferenceAbsoluteDate(final SatelliteSystem satellite,
final TimeScales timeScales) {
switch (satellite) {
case GPS : return timeScales.getGpsEpoch();
case GALILEO : return timeScales.getGalileoEpoch();
case QZSS : return timeScales.getQzssEpoch();
case BEIDOU : return timeScales.getBeidouEpoch();
case IRNSS : return timeScales.getIrnssEpoch();
case SBAS : return timeScales.getGpsEpoch();
default : throw new OrekitException(OrekitMessages.INVALID_SATELLITE_SYSTEM, satellite);
}
}
/** Get the reference epoch of the week number for the given satellite system.
* <p> Returned parameter is a DateComponents. </p>
* @param satellite satellite system
* @return the reference epoch
*/
private DateComponents getWeekReferenceDateComponents(final SatelliteSystem satellite) {
switch (satellite) {
case GPS : return DateComponents.GPS_EPOCH;
case GALILEO : return DateComponents.GALILEO_EPOCH;
case QZSS : return DateComponents.QZSS_EPOCH;
case BEIDOU : return DateComponents.BEIDOU_EPOCH;
case IRNSS : return DateComponents.IRNSS_EPOCH;
case SBAS : return DateComponents.GPS_EPOCH;
default : throw new OrekitException(OrekitMessages.INVALID_SATELLITE_SYSTEM, satellite);
}
}
/** 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(weekNumber, milliInWeek, system);
}
/** Internal class used only for serialization. */
@DefaultDataContext
private static class DataTransferObject implements Serializable {
/** Serializable UID. */
private static final long serialVersionUID = 201902141L;
/** Week number since the GNSS reference epoch. */
private final int weekNumber;
/** Number of milliseconds since week start. */
private final double milliInWeek;
/** Satellite system to consider. */
private final SatelliteSystem system;
/** Simple constructor.
* @param weekNumber week number since the GNSS reference epoch
* @param milliInWeek number of milliseconds since week start
* @param system satellite system to consider
*/
DataTransferObject(final int weekNumber, final double milliInWeek,
final SatelliteSystem system) {
this.weekNumber = weekNumber;
this.milliInWeek = milliInWeek;
this.system = system;
}
/** Replace the deserialized data transfer object with a {@link GNSSDate}.
* @return replacement {@link GNSSDate}
*/
private Object readResolve() {
return new GNSSDate(weekNumber, milliInWeek, system);
}
}
/** Enumerate for GNSS data. */
private enum GNSSDateType {
/** GPS. */
GPS(SatelliteSystem.GPS, 1024),
/** Galileo. */
GALILEO(SatelliteSystem.GALILEO, 4096),
/** QZSS. */
QZSS(SatelliteSystem.QZSS, 1024),
/** BeiDou. */
BEIDOU(SatelliteSystem.BEIDOU, 8192),
/** IRNSS. */
IRNSS(SatelliteSystem.IRNSS, 1024),
/** SBAS. */
SBAS(SatelliteSystem.SBAS, 1024);
/** Map for the number of week in one GNSS rollover cycle. */
private static final Map<SatelliteSystem, Integer> CYCLE_MAP = new HashMap<SatelliteSystem, Integer>();
static {
for (final GNSSDateType type : values()) {
final int val = type.getRollOverCycle();
final SatelliteSystem satellite = type.getSatelliteSystem();
CYCLE_MAP.put(satellite, val);
}
}
/** Number of week in one rollover cycle. */
private final int numberOfWeek;
/** Satellite system. */
private final SatelliteSystem satelliteSystem;
/**
* Build a new instance.
*
* @param system satellite system
* @param rollover number of week in one rollover cycle
*/
GNSSDateType(final SatelliteSystem system, final int rollover) {
this.satelliteSystem = system;
this.numberOfWeek = rollover;
}
/** Get the number of week in one rollover cycle.
* @return the number of week in one rollover cycle
*/
private int getRollOverCycle() {
return numberOfWeek;
}
/** Get the satellite system.
* @return the satellite system
*/
private SatelliteSystem getSatelliteSystem() {
return satelliteSystem;
}
/** Get the number of week in one rollover cycle for the given satellite system.
*
* @param satellite satellite system
* @return the number of week in one rollover cycle for the given satellite system
*/
private static int getRollOverWeek(final SatelliteSystem satellite) {
return CYCLE_MAP.get(satellite);
}
}
}