GNSSDate.java

  1. /* Copyright 2002-2020 CS GROUP
  2.  * Licensed to CS GROUP (CS) under one or more
  3.  * contributor license agreements.  See the NOTICE file distributed with
  4.  * this work for additional information regarding copyright ownership.
  5.  * CS licenses this file to You under the Apache License, Version 2.0
  6.  * (the "License"); you may not use this file except in compliance with
  7.  * the License.  You may obtain a copy of the License at
  8.  *
  9.  *   http://www.apache.org/licenses/LICENSE-2.0
  10.  *
  11.  * Unless required by applicable law or agreed to in writing, software
  12.  * distributed under the License is distributed on an "AS IS" BASIS,
  13.  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  14.  * See the License for the specific language governing permissions and
  15.  * limitations under the License.
  16.  */
  17. package org.orekit.time;

  19. import java.io.Serializable;
  20. import java.util.HashMap;
  21. import java.util.List;
  22. import java.util.Map;
  23. import java.util.concurrent.atomic.AtomicReference;

  25. import org.hipparchus.util.FastMath;
  26. import org.orekit.annotation.DefaultDataContext;
  27. import org.orekit.data.DataContext;
  28. import org.orekit.errors.OrekitException;
  29. import org.orekit.errors.OrekitMessages;
  30. import org.orekit.frames.EOPEntry;
  31. import org.orekit.gnss.SatelliteSystem;
  32. import org.orekit.utils.Constants;
  33. import org.orekit.utils.IERSConventions;

  35. /** Container for date in GNSS form.
  36.  * <p> This class can be used to handle {@link SatelliteSystem#GPS GPS},
  37.  * {@link SatelliteSystem#GALILEO Galileo}, {@link SatelliteSystem#BEIDOU BeiDou}
  38.  * and {@link SatelliteSystem#QZSS QZSS} dates. </p>
  39.  * @author Luc Maisonobe (original code)
  40.  * @author Bryan Cazabonne (generalization to all GNSS constellations)
  41.  * @see AbsoluteDate
  42.  */
  43. public class GNSSDate implements Serializable, TimeStamped {

  45.     /** Serializable UID. */
  46.     private static final long serialVersionUID = 201902141L;

  48.     /** Duration of a week in days. */
  49.     private static final int WEEK_D = 7;

  51.     /** Duration of a week in seconds. */
  52.     private static final double WEEK_S = WEEK_D * Constants.JULIAN_DAY;

  54.     /** Conversion factor from seconds to milliseconds. */
  55.     private static final double S_TO_MS = 1000.0;

  57.     /** Reference date for ensuring continuity across GNSS week rollover.
  58.      * @since 9.3.1
  59.      */
  60.     private static AtomicReference<DateComponents> rolloverReference = new AtomicReference<DateComponents>(null);

  62.     /** Week number since the GNSS reference epoch. */
  63.     private final int weekNumber;

  65.     /** Number of milliseconds since week start. */
  66.     private final double milliInWeek;

  68.     /** Satellite system to consider. */
  69.     private final SatelliteSystem system;

  71.     /** Corresponding date. */
  72.     private final transient AbsoluteDate date;

  74.     /** Build an instance corresponding to a GNSS date.
  75.      * <p>
  76.      * GNSS dates are provided as a week number starting at
  77.      * the GNSS reference epoch and as a number of milliseconds
  78.      * since week start.
  79.      * </p>
  80.      * <p>
  81.      * Many interfaces provide week number modulo the constellation week cycle. In order to cope with
  82.      * this, when the week number is smaller than the week cycle, this constructor assumes a modulo operation
  83.      * has been performed and it will fix the week number according to the reference date set up for
  84.      * handling rollover (see {@link #setRolloverReference(DateComponents) setRolloverReference(reference)}).
  85.      * If the week number is equal to the week cycle or larger, it will be used without any correction.
  86.      * </p>
  87.      *
  88.      * <p>This method uses the {@link DataContext#getDefault() default data context}.
  89.      *
  90.      * @param weekNumber week number
  91.      * @param milliInWeek number of milliseconds since week start
  92.      * @param system satellite system to consider
  93.      * @see #GNSSDate(int, double, SatelliteSystem, TimeScales)
  94.      */
  95.     @DefaultDataContext
  96.     public GNSSDate(final int weekNumber, final double milliInWeek,
  97.                     final SatelliteSystem system) {
  98.         this(weekNumber, milliInWeek, system, DataContext.getDefault().getTimeScales());
  99.     }

  101.     /**
  102.      * Build an instance corresponding to a GNSS date.
  103.      * <p>
  104.      * GNSS dates are provided as a week number starting at the GNSS reference epoch and
  105.      * as a number of milliseconds since week start.
  106.      * </p>
  107.      * <p>
  108.      * Many interfaces provide week number modulo the constellation week cycle. In order
  109.      * to cope with this, when the week number is smaller than the week cycle, this
  110.      * constructor assumes a modulo operation has been performed and it will fix the week
  111.      * number according to the reference date set up for handling rollover (see {@link
  112.      * #setRolloverReference(DateComponents) setRolloverReference(reference)}). If the
  113.      * week number is equal to the week cycle or larger, it will be used without any
  114.      * correction.
  115.      * </p>
  116.      *
  117.      * @param weekNumber  week number
  118.      * @param milliInWeek number of milliseconds since week start
  119.      * @param system      satellite system to consider
  120.      * @param timeScales  the set of time scales. Used to retrieve the appropriate time
  121.      *                    scale for the given {@code system}.
  122.      * @since 10.1
  123.      */
  124.     public GNSSDate(final int weekNumber,
  125.                     final double milliInWeek,
  126.                     final SatelliteSystem system,
  127.                     final TimeScales timeScales) {

  129.         final int day = (int) FastMath.floor(milliInWeek / (Constants.JULIAN_DAY * S_TO_MS));
  130.         final double secondsInDay = milliInWeek / S_TO_MS - day * Constants.JULIAN_DAY;

  132.         int w = weekNumber;
  133.         DateComponents dc = new DateComponents(getWeekReferenceDateComponents(system), weekNumber * 7 + day);
  134.         final int cycleW = GNSSDateType.getRollOverWeek(system);
  135.         if (weekNumber < cycleW) {

  137.             DateComponents reference = rolloverReference.get();
  138.             if (reference == null) {
  139.                 // lazy setting of a default reference, using end of EOP entries
  140.                 final UT1Scale       ut1       = timeScales.getUT1(IERSConventions.IERS_2010, true);
  141.                 final List<EOPEntry> eop       = ut1.getEOPHistory().getEntries();
  142.                 final int            lastMJD   = eop.get(eop.size() - 1).getMjd();
  143.                 reference = new DateComponents(DateComponents.MODIFIED_JULIAN_EPOCH, lastMJD);
  144.                 rolloverReference.compareAndSet(null, reference);
  145.             }

  147.             // fix GNSS week rollover
  148.             final int cycleD = WEEK_D * cycleW;
  149.             while (dc.getJ2000Day() < reference.getJ2000Day() - cycleD / 2) {
  150.                 dc = new DateComponents(dc, cycleD);
  151.                 w += cycleW;
  152.             }

  154.         }

  156.         this.weekNumber  = w;
  157.         this.milliInWeek = milliInWeek;
  158.         this.system      = system;

  160.         date = new AbsoluteDate(dc, new TimeComponents(secondsInDay), getTimeScale(system, timeScales));

  162.     }

  164.     /** Build an instance from an absolute date.
  165.      *
  166.      * <p>This method uses the {@link DataContext#getDefault() default data context}.
  167.      *
  168.      * @param date absolute date to consider
  169.      * @param system satellite system to consider
  170.      * @see #GNSSDate(AbsoluteDate, SatelliteSystem, TimeScales)
  171.      */
  172.     @DefaultDataContext
  173.     public GNSSDate(final AbsoluteDate date, final SatelliteSystem system) {
  174.         this(date, system, DataContext.getDefault().getTimeScales());
  175.     }

  177.     /**
  178.      * Build an instance from an absolute date.
  179.      *
  180.      * @param date       absolute date to consider
  181.      * @param system     satellite system to consider
  182.      * @param timeScales the set of time scales. Used to retrieve the appropriate time
  183.      *                   scale for the given {@code system}.
  184.      * @since 10.1
  185.      */
  186.     public GNSSDate(final AbsoluteDate date,
  187.                     final SatelliteSystem system,
  188.                     final TimeScales timeScales) {

  190.         this.system = system;
  191.         final AbsoluteDate epoch = getWeekReferenceAbsoluteDate(system, timeScales);
  192.         this.weekNumber  = (int) FastMath.floor(date.durationFrom(epoch) / WEEK_S);
  193.         final AbsoluteDate weekStart = new AbsoluteDate(epoch, WEEK_S * weekNumber);
  194.         this.milliInWeek = date.durationFrom(weekStart) * S_TO_MS;
  195.         this.date        = date;

  197.     }

  199.     /** Set a reference date for ensuring continuity across GNSS week rollover.
  200.      * <p>
  201.      * Instance created using the {@link #GNSSDate(int, double, SatelliteSystem) GNSSDate(weekNumber, milliInWeek, system)}
  202.      * constructor and with a week number between 0 and the constellation week cycle (cycleW) after this method has been called will
  203.      * fix the week number to ensure they correspond to dates between {@code reference - cycleW / 2 weeks}
  204.      * and {@code reference + cycleW / 2 weeks}.
  205.      * </p>
  206.      * <p>
  207.      * If this method is never called, a default reference date for rollover will be set using
  208.      * the date of the last known EOP entry retrieved from {@link UT1Scale#getEOPHistory() UT1}
  209.      * time scale.
  210.      * </p>
  211.      * @param reference reference date for GNSS week rollover
  212.      * @see #getRolloverReference()
  213.      * @see #GNSSDate(int, double, SatelliteSystem)
  214.      * @since 9.3.1
  215.      */
  216.     public static void setRolloverReference(final DateComponents reference) {
  217.         rolloverReference.set(reference);
  218.     }

  220.     /** Get the reference date ensuring continuity across GNSS week rollover.
  221.      * @return reference reference date for GNSS week rollover
  222.      * @see #setRolloverReference(DateComponents)
  223.      * @see #GNSSDate(int, double, SatelliteSystem)
  224.      * @since 9.3.1
  225.      */
  226.     public static DateComponents getRolloverReference() {
  227.         return rolloverReference.get();
  228.     }

  230.     /** Get the week number since the GNSS reference epoch.
  231.      * <p>
  232.      * The week number returned here has been fixed for GNSS week rollover, i.e.
  233.      * it may be larger than the corresponding week cycle of the constellation.
  234.      * </p>
  235.      * @return week number since since the GNSS reference epoch
  236.      */
  237.     public int getWeekNumber() {
  238.         return weekNumber;
  239.     }

  241.     /** Get the number of milliseconds since week start.
  242.      * @return number of milliseconds since week start
  243.      */
  244.     public double getMilliInWeek() {
  245.         return milliInWeek;
  246.     }

  248.     /** {@inheritDoc} */
  249.     @Override
  250.     public AbsoluteDate getDate() {
  251.         return date;
  252.     }

  254.     /** Get the time scale related to the given satellite system.
  255.      * @param satellite satellite system
  256.      * @param timeScales set of time scales.
  257.      * @return the time scale
  258.      */
  259.     private TimeScale getTimeScale(final SatelliteSystem satellite,
  260.                                    final TimeScales timeScales) {
  261.         switch (satellite) {
  262.             case GPS     : return timeScales.getGPS();
  263.             case GALILEO : return timeScales.getGST();
  264.             case QZSS    : return timeScales.getQZSS();
  265.             case BEIDOU  : return timeScales.getBDT();
  266.             case IRNSS   : return timeScales.getIRNSS();
  267.             case SBAS    : return timeScales.getGPS();
  268.             default      : throw new OrekitException(OrekitMessages.INVALID_SATELLITE_SYSTEM, satellite);
  269.         }
  270.     }

  272.     /** Get the reference epoch of the week number for the given satellite system.
  273.      * <p> Returned parameter is an AbsoluteDate. </p>
  274.      * @param satellite satellite system
  275.      * @param timeScales set of time scales.
  276.      * @return the reference epoch
  277.      */
  278.     private AbsoluteDate getWeekReferenceAbsoluteDate(final SatelliteSystem satellite,
  279.                                                       final TimeScales timeScales) {
  280.         switch (satellite) {
  281.             case GPS     : return timeScales.getGpsEpoch();
  282.             case GALILEO : return timeScales.getGalileoEpoch();
  283.             case QZSS    : return timeScales.getQzssEpoch();
  284.             case BEIDOU  : return timeScales.getBeidouEpoch();
  285.             case IRNSS   : return timeScales.getIrnssEpoch();
  286.             case SBAS    : return timeScales.getGpsEpoch();
  287.             default      : throw new OrekitException(OrekitMessages.INVALID_SATELLITE_SYSTEM, satellite);
  288.         }
  289.     }

  291.     /** Get the reference epoch of the week number for the given satellite system.
  292.      * <p> Returned parameter is a DateComponents. </p>
  293.      * @param satellite satellite system
  294.      * @return the reference epoch
  295.      */
  296.     private DateComponents getWeekReferenceDateComponents(final SatelliteSystem satellite) {
  297.         switch (satellite) {
  298.             case GPS     : return DateComponents.GPS_EPOCH;
  299.             case GALILEO : return DateComponents.GALILEO_EPOCH;
  300.             case QZSS    : return DateComponents.QZSS_EPOCH;
  301.             case BEIDOU  : return DateComponents.BEIDOU_EPOCH;
  302.             case IRNSS   : return DateComponents.IRNSS_EPOCH;
  303.             case SBAS    : return DateComponents.GPS_EPOCH;
  304.             default      : throw new OrekitException(OrekitMessages.INVALID_SATELLITE_SYSTEM, satellite);
  305.         }
  306.     }

  308.     /** Replace the instance with a data transfer object for serialization.
  309.      * @return data transfer object that will be serialized
  310.      */
  311.     @DefaultDataContext
  312.     private Object writeReplace() {
  313.         return new DataTransferObject(weekNumber, milliInWeek, system);
  314.     }

  316.     /** Internal class used only for serialization. */
  317.     @DefaultDataContext
  318.     private static class DataTransferObject implements Serializable {

  320.         /** Serializable UID. */
  321.         private static final long serialVersionUID = 201902141L;

  323.         /** Week number since the GNSS reference epoch. */
  324.         private final int weekNumber;

  326.         /** Number of milliseconds since week start. */
  327.         private final double milliInWeek;

  329.         /** Satellite system to consider. */
  330.         private final SatelliteSystem system;

  332.         /** Simple constructor.
  333.          * @param weekNumber week number since the GNSS reference epoch
  334.          * @param milliInWeek number of milliseconds since week start
  335.          * @param system satellite system to consider
  336.          */
  337.         DataTransferObject(final int weekNumber, final double milliInWeek,
  338.                            final SatelliteSystem system) {
  339.             this.weekNumber  = weekNumber;
  340.             this.milliInWeek = milliInWeek;
  341.             this.system      = system;
  342.         }

  344.         /** Replace the deserialized data transfer object with a {@link GNSSDate}.
  345.          * @return replacement {@link GNSSDate}
  346.          */
  347.         private Object readResolve() {
  348.             return new GNSSDate(weekNumber, milliInWeek, system);
  349.         }

  351.     }

  353.     /** Enumerate for GNSS data. */
  354.     private enum GNSSDateType {

  356.         /** GPS. */
  357.         GPS(SatelliteSystem.GPS, 1024),

  359.         /** Galileo. */
  360.         GALILEO(SatelliteSystem.GALILEO, 4096),

  362.         /** QZSS. */
  363.         QZSS(SatelliteSystem.QZSS, 1024),

  365.         /** BeiDou. */
  366.         BEIDOU(SatelliteSystem.BEIDOU, 8192),

  368.         /** IRNSS. */
  369.         IRNSS(SatelliteSystem.IRNSS, 1024),

  371.         /** SBAS. */
  372.         SBAS(SatelliteSystem.SBAS, 1024);

  374.         /** Map for the number of week in one GNSS rollover cycle. */
  375.         private static final Map<SatelliteSystem, Integer> CYCLE_MAP = new HashMap<SatelliteSystem, Integer>();
  376.         static {
  377.             for (final GNSSDateType type : values()) {
  378.                 final int             val       = type.getRollOverCycle();
  379.                 final SatelliteSystem satellite = type.getSatelliteSystem();
  380.                 CYCLE_MAP.put(satellite, val);
  381.             }
  382.         }

  384.         /** Number of week in one rollover cycle. */
  385.         private final int numberOfWeek;

  387.         /** Satellite system. */
  388.         private final SatelliteSystem satelliteSystem;

  390.         /**
  391.          * Build a new instance.
  392.          *
  393.          * @param system satellite system
  394.          * @param rollover number of week in one rollover cycle
  395.          */
  396.         GNSSDateType(final SatelliteSystem system, final int rollover) {
  397.             this.satelliteSystem = system;
  398.             this.numberOfWeek    = rollover;
  399.         }

  401.         /** Get the number of week in one rollover cycle.
  402.          * @return  the number of week in one rollover cycle
  403.          */
  404.         private int getRollOverCycle() {
  405.             return numberOfWeek;
  406.         }

  408.         /** Get the satellite system.
  409.          * @return the satellite system
  410.          */
  411.         private SatelliteSystem getSatelliteSystem() {
  412.             return satelliteSystem;
  413.         }

  415.         /** Get the number of week in one rollover cycle for the given satellite system.
  416.          *
  417.          * @param satellite satellite system
  418.          * @return the number of week in one rollover cycle for the given satellite system
  419.          */
  420.         private static int getRollOverWeek(final SatelliteSystem satellite) {
  421.             return CYCLE_MAP.get(satellite);
  422.         }

  424.     }
  425. }
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