RelativeProvider.java

/* Copyright 2002-2026 CS GROUP
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 * 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,
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package org.orekit.propagation.relative;

import org.orekit.frames.Frame;
import org.orekit.frames.LOF;
import org.orekit.frames.Transform;
import org.orekit.orbits.Orbit;
import org.orekit.propagation.AdditionalDataProvider;
import org.orekit.propagation.SpacecraftState;
import org.orekit.utils.TimeStampedPVCoordinates;

/**
 * Interface for relative provider.
 * <p>
 * A relative provider is an interface extending AdditionalDataProvider to provide the relative state of a chaser S/C in
 * regard to a target S/C as an AdditionalData. The target S/C is propagated with the "main" propagator where the
 * additional data is added.
 * </p>
 *
 * @author Romain Cuvillon
 * @since 14.0
 */
public interface RelativeProvider extends AdditionalDataProvider<double[]> {

    /**
     * Returns the LOF used by the provider.
     * @return the LOF used by the provider
     */
    LOF getLof();

    /**
     * Get the initial TimeStampedPVCoordinates of the chaser in the Local Orbital Frame of the target.
     *
     * @return initial TimeStampedPVCoordinates of the chaser in target's LOF
     */
    TimeStampedPVCoordinates getInitialChaserPVTLof();

    /**
     * Set the initial TimeStampedPVCoordinates of the chaser in the Local Orbital Frame of the target.
     *
     * @param initialChaserPVTLof initial TimeStampedPVCoordinates of the chaser in target's LOF
     */
    void setInitialChaserPVTLof(TimeStampedPVCoordinates initialChaserPVTLof);

    /**
     * Extracts the chaser's PVT in the target LOF from the given target {@link SpacecraftState}.
     *
     * @param targetState target SpacecraftState
     * @return chaser's TimeStampedPVCoordinates in target's LOF
     */
    TimeStampedPVCoordinates extractChaserPVT(SpacecraftState targetState);

    /**
     * Extracts the chaser's PVT from the given target {@link SpacecraftState} and converts it to the desired output
     * frame.
     *
     * @param targetState target SpacecraftState
     * @param outputFrame desired frame in which to extract chaser's TimeStampedPVCoordinates
     * @return TimeStampedPVCoordinates in desired frame
     */
    default TimeStampedPVCoordinates extractChaserPVT(final SpacecraftState targetState, final Frame outputFrame) {

        // Extract chaser PVT in target's LOF
        final TimeStampedPVCoordinates chaserPVTLOF = extractChaserPVT(targetState);

        // Transform PVT from target's LOF to reference inertial frame
        final Transform lofToInertial =
                        getLof().transformFromInertial(targetState.getDate(),
                                                       targetState.getPVCoordinates()).getInverse();
        final TimeStampedPVCoordinates pvInertial = lofToInertial.transformPVCoordinates(chaserPVTLOF);

        // Transform PVT from reference inertial frame to desired output frame
        final Transform inertialToOutputFrame = targetState.getFrame().getTransformTo(outputFrame,
                                                                                      targetState.getDate());
        return inertialToOutputFrame.transformPVCoordinates(pvInertial);
    }

    /**
     * Get the chaser state relative to a target, in target's LVLH LOF.
     *
     * @param spacecraftState spacecraft state to which additional data should correspond
     * @return chaser Cartesian state in target's LVLH Local Orbital Frame.
     */
    @Override
    default double[] getAdditionalData(final SpacecraftState spacecraftState) {

        // Extract chaser PVT in target's LOF
        final TimeStampedPVCoordinates pvt = extractChaserPVT(spacecraftState);

        // Return a double[] to comply with
        return new double[] {
                        pvt.getPosition().getX(), pvt.getPosition().getY(), pvt.getPosition().getZ(),
                        pvt.getVelocity().getX(), pvt.getVelocity().getY(), pvt.getVelocity().getZ()
        };
    }

    /**
     * Get orbit of the target.
     *
     * @return orbit of the target
     */
    Orbit getTargetOrbit();

    /**
     * Set orbit of the target.
     *
     * @param targetOrbit orbit of the target
     */
    void setTargetOrbit(Orbit targetOrbit);

    /**
     * CW doesn't use true anomaly, so default is a no-op Set the true anomaly of the target.
     *
     * @param trueAnomaly true anomaly of the target
     */
    default void setTargetTrueAnomaly(final double trueAnomaly) {
    }
}