AbstractTimeScales.java

/* Contributed in the public domain.
 * 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.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;

import org.hipparchus.util.MathArrays;
import org.hipparchus.util.Pair;
import org.orekit.frames.EOPHistory;
import org.orekit.utils.Constants;
import org.orekit.utils.IERSConventions;

/**
 * Abstract base class for {@link TimeScales} that implements some common functionality.
 *
 * @author Evan Ward
 * @author Luc Maisonobe
 * @since 10.1
 */
public abstract class AbstractTimeScales implements TimeScales {

    /** GMST time scales. */
    private final ConcurrentMap<Pair<IERSConventions, Boolean>, GMSTScale> gmstMap;
    /** UT1 time scales. */
    private final ConcurrentMap<Pair<IERSConventions, Boolean>, UT1Scale> ut1Map;

    /** Simple constructor. */
    public AbstractTimeScales() {
        final int n = IERSConventions.values().length;
        gmstMap = new ConcurrentHashMap<>(n * 2);
        ut1Map = new ConcurrentHashMap<>(n * 2);
    }

    /**
     * Get the Universal Time 1 scale.
     * <p>
     * As this method allow associating any history with the time scale, it may involve
     * large data sets. So this method does <em>not</em> cache the resulting {@link
     * UT1Scale UT1Scale} instance, a new instance will be returned each time. In order to
     * avoid wasting memory, calling {@link #getUT1(IERSConventions, boolean)} with the
     * single enumerate corresponding to the conventions may be a better solution. This
     * method is made available only for expert use.
     * </p>
     *
     * @param history EOP parameters providing dUT1 (may be null if no correction is
     *                desired)
     * @return Universal Time 1 scale
     * @see #getUT1(IERSConventions, boolean)
     */
    protected UT1Scale getUT1(final EOPHistory history) {
        return new UT1Scale(history, getUTC());
    }

    /**
     * Get the EOP history for the given conventions.
     *
     * @param conventions to use in computing the EOP history.
     * @param simpleEOP   whether to ignore some small tidal effects.
     * @return EOP history.
     */
    protected abstract EOPHistory getEopHistory(IERSConventions conventions,
                                                boolean simpleEOP);

    @Override
    public UT1Scale getUT1(final IERSConventions conventions, final boolean simpleEOP) {
        final Pair<IERSConventions, Boolean> key = new Pair<>(conventions, simpleEOP);
        synchronized (this) {
            return ut1Map.computeIfAbsent(key, k -> getUT1(getEopHistory(conventions, simpleEOP)));
        }
    }

    @Override
    public GMSTScale getGMST(final IERSConventions conventions, final boolean simpleEOP) {
        final Pair<IERSConventions, Boolean> key = new Pair<>(conventions, simpleEOP);
        synchronized (this) {
            return gmstMap.computeIfAbsent(key, k -> new GMSTScale(getUT1(conventions, simpleEOP)));
        }
    }

    @Override
    public AbsoluteDate getJulianEpoch() {
        return new AbsoluteDate(DateComponents.JULIAN_EPOCH, TimeComponents.H12, this.getTT());
    }

    @Override
    public AbsoluteDate getModifiedJulianEpoch() {
        return new AbsoluteDate(DateComponents.MODIFIED_JULIAN_EPOCH, TimeComponents.H00, this.getTT());
    }

    @Override
    public AbsoluteDate getFiftiesEpoch() {
        return new AbsoluteDate(DateComponents.FIFTIES_EPOCH, TimeComponents.H00, this.getTT());
    }

    @Override
    public AbsoluteDate getCcsdsEpoch() {
        return new AbsoluteDate(DateComponents.CCSDS_EPOCH, TimeComponents.H00, this.getTAI());
    }

    @Override
    public AbsoluteDate getGalileoEpoch() {
        return new AbsoluteDate(DateComponents.GALILEO_EPOCH, TimeComponents.H00, this.getGST());
    }

    @Override
    public AbsoluteDate getGpsEpoch() {
        return new AbsoluteDate(DateComponents.GPS_EPOCH, TimeComponents.H00, this.getGPS());
    }

    @Override
    public AbsoluteDate getQzssEpoch() {
        return new AbsoluteDate(DateComponents.QZSS_EPOCH, TimeComponents.H00, this.getQZSS());
    }

    @Override
    public AbsoluteDate getNavicEpoch() {
        return new AbsoluteDate(DateComponents.NAVIC_EPOCH, TimeComponents.H00, this.getNavIC());
    }

    @Override
    public AbsoluteDate getBeidouEpoch() {
        return new AbsoluteDate(DateComponents.BEIDOU_EPOCH, TimeComponents.H00, this.getBDT());
    }

    @Override
    public AbsoluteDate getGlonassEpoch() {
        return new AbsoluteDate(DateComponents.GLONASS_EPOCH,
                                new TimeComponents(new TimeOffset(29L, 0L)), this.getTAI()).shiftedBy(new TimeOffset(-10800L, 0L));
    }

    @Override
    public AbsoluteDate getJ2000Epoch() {
        return new AbsoluteDate(DateComponents.J2000_EPOCH, TimeComponents.H12, this.getTT());
    }

    @Override
    public AbsoluteDate getJavaEpoch() {
        return new AbsoluteDate(DateComponents.JAVA_EPOCH, this.getTAI()).shiftedBy(new TimeOffset(8L, 82000000000000L));
    }

    @Override
    public AbsoluteDate getPastInfinity() {
        return getJavaEpoch().shiftedBy(Double.NEGATIVE_INFINITY);
    }

    @Override
    public AbsoluteDate getFutureInfinity() {
        return getJavaEpoch().shiftedBy(Double.POSITIVE_INFINITY);
    }

    @Override
    public AbsoluteDate createJulianEpoch(final double julianEpoch) {
        return new AbsoluteDate(getJ2000Epoch(),
                Constants.JULIAN_YEAR * (julianEpoch - 2000.0));
    }

    @Override
    public AbsoluteDate createBesselianEpoch(final double besselianEpoch) {
        return new AbsoluteDate(getJ2000Epoch(),
                MathArrays.linearCombination(
                        Constants.BESSELIAN_YEAR, besselianEpoch - 1900,
                        Constants.JULIAN_DAY, -36525,
                        Constants.JULIAN_DAY, 0.31352));
    }

}