NodeDetector.java
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package org.orekit.propagation.events;
import org.hipparchus.ode.events.Action;
import org.hipparchus.util.FastMath;
import org.hipparchus.util.MathUtils;
import org.orekit.frames.Frame;
import org.orekit.orbits.KeplerianOrbit;
import org.orekit.orbits.Orbit;
import org.orekit.orbits.OrbitType;
import org.orekit.orbits.PositionAngleType;
import org.orekit.propagation.SpacecraftState;
import org.orekit.propagation.events.handlers.EventHandler;
import org.orekit.propagation.events.handlers.StopOnIncreasing;
/** Finder for node crossing events.
* <p>This class finds equator crossing events (i.e. ascending
* or descending node crossing).</p>
* <p>The default implementation behavior is to {@link Action#CONTINUE continue}
* propagation at descending node crossing and to {@link Action#STOP stop} propagation
* at ascending node crossing. This can be changed by calling
* {@link #withHandler(EventHandler)} after construction.</p>
* <p>Beware that node detection will fail for almost equatorial orbits. If
* for example a node detector is used to trigger an {@link
* org.orekit.forces.maneuvers.ImpulseManeuver ImpulseManeuver} and the maneuver
* turn the orbit plane to equator, then the detector may completely fail just
* after the maneuver has been performed! This is a real case that has been
* encountered during validation ...</p>
* @see org.orekit.propagation.Propagator#addEventDetector(EventDetector)
* @author Luc Maisonobe
*/
public class NodeDetector extends AbstractDetector<NodeDetector> {
/** Default max check interval. */
private static final double DEFAULT_MAX_CHECK = 1800.0;
/** Default convergence threshold. */
private static final double DEFAULT_THRESHOLD = 1.0e-3;
/** Frame in which the equator is defined. */
private final Frame frame;
/** Build a new instance.
* <p>The default {@link #getMaxCheckInterval() max check interval}
* is set to 1800s, it can be changed using {@link #withMaxCheck(double)}
* in the fluent API. The default {@link #getThreshold() convergence threshold}
* is set to 1.0e-3s, it can be changed using {@link #withThreshold(double)}
* in the fluent API.</p>
* @param frame frame in which the equator is defined (typical
* values are {@link org.orekit.frames.FramesFactory#getEME2000() EME<sub>2000</sub>} or
* {@link org.orekit.frames.FramesFactory#getITRF(org.orekit.utils.IERSConventions, boolean) ITRF})
* @since 10.3
*/
public NodeDetector(final Frame frame) {
this(s -> DEFAULT_MAX_CHECK, DEFAULT_THRESHOLD, DEFAULT_MAX_ITER,
new StopOnIncreasing(), frame);
}
/** Build a new instance.
* <p>The orbit is used only to set an upper bound for the max check interval
* to a value related to nodes separation (as computed by a Keplerian model)
* and to set the convergence threshold according to orbit size.</p>
* @param orbit initial orbit
* @param frame frame in which the equator is defined (typical
* values are {@link org.orekit.frames.FramesFactory#getEME2000() EME<sub>2000</sub>} or
* {@link org.orekit.frames.FramesFactory#getITRF(org.orekit.utils.IERSConventions, boolean) ITRF})
*/
public NodeDetector(final Orbit orbit, final Frame frame) {
this(1.0e-13 * orbit.getKeplerianPeriod(), orbit, frame);
}
/** Build a new instance.
* <p>The orbit is used only to set an upper bound for the max check interval
* to a value related to nodes separation (as computed by a Keplerian model).</p>
* @param threshold convergence threshold (s)
* @param orbit initial orbit
* @param frame frame in which the equator is defined (typical
* values are {@link org.orekit.frames.FramesFactory#getEME2000() EME<sub>2000</sub>} or
* {@link org.orekit.frames.FramesFactory#getITRF(org.orekit.utils.IERSConventions, boolean) ITRF})
*/
public NodeDetector(final double threshold, final Orbit orbit, final Frame frame) {
this(s -> 2 * estimateNodesTimeSeparation(orbit) / 3, threshold,
DEFAULT_MAX_ITER, new StopOnIncreasing(),
frame);
}
/** 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
* @param frame frame in which the equator is defined (typical
* values are {@link org.orekit.frames.FramesFactory#getEME2000() EME<sub>2000</sub>} or
* {@link org.orekit.frames.FramesFactory#getITRF(org.orekit.utils.IERSConventions, boolean) ITRF})
* @since 6.1
*/
protected NodeDetector(final AdaptableInterval maxCheck, final double threshold,
final int maxIter, final EventHandler handler,
final Frame frame) {
super(maxCheck, threshold, maxIter, handler);
this.frame = frame;
}
/** {@inheritDoc} */
@Override
protected NodeDetector create(final AdaptableInterval newMaxCheck, final double newThreshold,
final int newMaxIter, final EventHandler newHandler) {
return new NodeDetector(newMaxCheck, newThreshold, newMaxIter, newHandler, frame);
}
/** Find time separation between nodes.
* <p>
* The estimation of time separation is based on Keplerian motion, it is only
* used as a rough guess for a safe setting of default max check interval for
* event detection.
* </p>
* @param orbit initial orbit
* @return minimum time separation between nodes
*/
private static double estimateNodesTimeSeparation(final Orbit orbit) {
final KeplerianOrbit keplerian = (KeplerianOrbit) OrbitType.KEPLERIAN.convertType(orbit);
// mean anomaly of ascending node
final double ascendingM = new KeplerianOrbit(keplerian.getA(), keplerian.getE(),
keplerian.getI(),
keplerian.getPerigeeArgument(),
keplerian.getRightAscensionOfAscendingNode(),
-keplerian.getPerigeeArgument(), PositionAngleType.TRUE,
keplerian.getFrame(), keplerian.getDate(),
keplerian.getMu()).getMeanAnomaly();
// mean anomaly of descending node
final double descendingM = new KeplerianOrbit(keplerian.getA(), keplerian.getE(),
keplerian.getI(),
keplerian.getPerigeeArgument(),
keplerian.getRightAscensionOfAscendingNode(),
FastMath.PI - keplerian.getPerigeeArgument(), PositionAngleType.TRUE,
keplerian.getFrame(), keplerian.getDate(),
keplerian.getMu()).getMeanAnomaly();
// differences between mean anomalies
final double delta1 = MathUtils.normalizeAngle(ascendingM, descendingM + FastMath.PI) - descendingM;
final double delta2 = 2 * FastMath.PI - delta1;
// minimum time separation between the two nodes
return FastMath.min(delta1, delta2) / keplerian.getKeplerianMeanMotion();
}
/** Get the frame in which the equator is defined.
* @return the frame in which the equator is defined
*/
public Frame getFrame() {
return frame;
}
/** Compute the value of the switching function.
* This function computes the Z position in the defined frame.
* @param s the current state information: date, kinematics, attitude
* @return value of the switching function
*/
public double g(final SpacecraftState s) {
return s.getPosition(frame).getZ();
}
}