FieldApsideDetector.java

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package org.orekit.propagation.events;

import org.hipparchus.CalculusFieldElement;
import org.hipparchus.geometry.euclidean.threed.FieldVector3D;
import org.hipparchus.ode.events.Action;
import org.orekit.orbits.FieldOrbit;
import org.orekit.propagation.FieldSpacecraftState;
import org.orekit.propagation.events.handlers.FieldEventHandler;
import org.orekit.propagation.events.handlers.FieldStopOnIncreasing;
import org.orekit.utils.FieldPVCoordinates;

/** Finder for apside crossing events.
 * <p>This class finds apside crossing events (i.e. apogee or perigee crossing).</p>
 * <p>The default implementation behavior is to {@link Action#CONTINUE continue}
 * propagation at apogee crossing and to {@link Action#STOP stop} propagation
 * at perigee crossing. This can be changed by calling
 * {@link #withHandler(FieldEventHandler)} after construction.</p>
 * <p>Beware that apside detection will fail for almost circular orbits. If
 * for example an apside detector is used to trigger an {@link
 * org.orekit.forces.maneuvers.ImpulseManeuver ImpulseManeuver} and the maneuver
 * change the orbit shape to circular, then the detector may completely fail just
 * after the maneuver has been performed!</p>
 * @see org.orekit.propagation.FieldPropagator#addEventDetector(FieldEventDetector)
 * @author Luc Maisonobe
 * @param <T> type of the field elements
 */
public class FieldApsideDetector<T extends CalculusFieldElement<T>> extends FieldAbstractDetector<FieldApsideDetector<T>, T> {

    /** Build a new instance.
     * <p>The orbit is used only to set an upper bound for the
     * max check interval to period/3 and to set the convergence
     * threshold according to orbit size</p>
     * @param orbit initial orbit
     */
    public FieldApsideDetector(final FieldOrbit<T> orbit) {
        this(orbit.getKeplerianPeriod().multiply(1.0e-13), orbit);
    }

    /** Build a new instance.
     * <p>The orbit is used only to set an upper bound for the
     * max check interval to period/3</p>
     * @param threshold convergence threshold (s)
     * @param orbit initial orbit
     */
    public FieldApsideDetector(final T threshold, final FieldOrbit<T> orbit) {
        super(s -> orbit.getKeplerianPeriod().divide(3).getReal(), threshold,
              DEFAULT_MAX_ITER, new FieldStopOnIncreasing<>());
    }

    /** Protected constructor with full parameters.
     * <p>
     * This constructor is not public as users are expected to use the builder
     * API with the various {@code withXxx()} methods to set up the instance
     * in a readable manner without using a huge amount of parameters.
     * </p>
     * @param maxCheck maximum checking interval
     * @param threshold convergence threshold (s)
     * @param maxIter maximum number of iterations in the event time search
     * @param handler event handler to call at event occurrences
     */
    protected FieldApsideDetector(final FieldAdaptableInterval<T> maxCheck, final T threshold,
                                  final int maxIter, final FieldEventHandler<T> handler) {
        super(maxCheck, threshold, maxIter, handler);
    }

    /** {@inheritDoc} */
    @Override
    protected FieldApsideDetector<T> create(final FieldAdaptableInterval<T> newMaxCheck, final T newThreshold,
                                            final int newMaxIter,
                                            final FieldEventHandler<T> newHandler) {
        return new FieldApsideDetector<>(newMaxCheck, newThreshold, newMaxIter, newHandler);
    }

    /** Compute the value of the switching function.
     * This function computes the dot product of the 2 vectors : position.velocity.
     * @param s the current state information: date, kinematics, attitude
     * @return value of the switching function
     */
    public T g(final FieldSpacecraftState<T> s) {
        final FieldPVCoordinates<T> pv = s.getPVCoordinates();
        return FieldVector3D.dotProduct(pv.getPosition(), pv.getVelocity());
    }

}