AngularRaDecBuilder.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
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package org.orekit.estimation.measurements.generation;

import org.hipparchus.random.CorrelatedRandomVectorGenerator;
import org.orekit.estimation.measurements.AngularRaDec;
import org.orekit.estimation.measurements.EstimationModifier;
import org.orekit.estimation.measurements.GroundStation;
import org.orekit.estimation.measurements.ObservableSatellite;
import org.orekit.frames.Frame;
import org.orekit.propagation.SpacecraftState;
import org.orekit.time.AbsoluteDate;
import org.orekit.utils.ParameterDriver;


/** Builder for {@link AngularRaDec} measurements.
 * @author Luc Maisonobe
 * @since 9.3
 */
public class AngularRaDecBuilder extends AbstractMeasurementBuilder<AngularRaDec> {

    /** Ground station from which measurement is performed. */
    private final GroundStation station;

    /** Reference frame in which the right ascension - declination angles are given. */
    private final Frame referenceFrame;

    /** Simple constructor.
     * @param noiseSource noise source, may be null for generating perfect measurements
     * @param station ground station from which measurement is performed
     * @param referenceFrame Reference frame in which the right ascension - declination angles are given
     * @param sigma theoretical standard deviation
     * @param baseWeight base weight
     * @param satellite satellite related to this builder
     */
    public AngularRaDecBuilder(final CorrelatedRandomVectorGenerator noiseSource,
                               final GroundStation station, final Frame referenceFrame,
                               final double[] sigma, final double[] baseWeight,
                               final ObservableSatellite satellite) {
        super(noiseSource, sigma, baseWeight, satellite);
        this.station        = station;
        this.referenceFrame = referenceFrame;
    }

    /** {@inheritDoc} */
    @Override
    public AngularRaDec build(final SpacecraftState[] states) {

        final ObservableSatellite satellite = getSatellites()[0];
        final double[] sigma                = getTheoreticalStandardDeviation();
        final double[] baseWeight           = getBaseWeight();
        final SpacecraftState[] relevant    = new SpacecraftState[] { states[satellite.getPropagatorIndex()] };

        // create a dummy measurement
        final AngularRaDec dummy = new AngularRaDec(station, referenceFrame, relevant[0].getDate(),
                                                    new double[] {
                                                        0.0, 0.0
                                                    }, sigma, baseWeight, satellite);
        for (final EstimationModifier<AngularRaDec> modifier : getModifiers()) {
            dummy.addModifier(modifier);
        }

        // set a reference date for parameters missing one
        for (final ParameterDriver driver : dummy.getParametersDrivers()) {
            if (driver.getReferenceDate() == null) {
                final AbsoluteDate start = getStart();
                final AbsoluteDate end   = getEnd();
                driver.setReferenceDate(start.durationFrom(end) <= 0 ? start : end);
            }
        }

        // estimate the perfect value of the measurement
        final double[] angular = dummy.estimate(0, 0, relevant).getEstimatedValue();

        // add the noise
        final double[] noise = getNoise();
        if (noise != null) {
            angular[0] += noise[0];
            angular[1] += noise[1];
        }

        // generate measurement
        final AngularRaDec measurement = new AngularRaDec(station, referenceFrame, relevant[0].getDate(),
                                                          angular, sigma, baseWeight, satellite);
        for (final EstimationModifier<AngularRaDec> modifier : getModifiers()) {
            measurement.addModifier(modifier);
        }
        return measurement;

    }

}