MagneticFieldDetector.java
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package org.orekit.propagation.events;
import org.orekit.annotation.DefaultDataContext;
import org.orekit.bodies.GeodeticPoint;
import org.orekit.bodies.OneAxisEllipsoid;
import org.orekit.data.DataContext;
import org.orekit.models.earth.GeoMagneticField;
import org.orekit.models.earth.GeoMagneticFieldFactory;
import org.orekit.models.earth.GeoMagneticFieldFactory.FieldModel;
import org.orekit.propagation.SpacecraftState;
import org.orekit.propagation.events.handlers.EventHandler;
import org.orekit.propagation.events.handlers.StopOnIncreasing;
import org.orekit.time.AbsoluteDate;
import org.orekit.time.TimeScale;
/** Detector for Earth magnetic field strength.
* <p>
* The detector is based on the field intensity calculated at the
* satellite's latitude and longitude, either at sea level or at
* satellite altitude, depending on the value chosen for the
* <code>atSeaLevel</code> indicator.<br>
* It can detect flyovers of the South-Atlantic anomaly with
* a classically accepted limit value of 32,000 nT at sea level.
* </p>
* @author Romaric Her
*/
public class MagneticFieldDetector extends AbstractDetector<MagneticFieldDetector> {
/** Fixed threshold value of Magnetic field to be crossed, in Teslas. */
private final double limit;
/** Switch for calculating field strength at sea level (true) or satellite altitude (false). */
private final boolean atSeaLevel;
/** Earth geomagnetic field. */
private GeoMagneticField field;
/** year of the current state. */
private double currentYear;
/** Earth geomagnetic field model. */
private final FieldModel model;
/** Earth body shape. */
private final OneAxisEllipsoid body;
/** Current data context. */
private final DataContext dataContext;
/** Build a new detector.
*
* <p>This constructor uses:
* <ul>
* <li>the {@link DataContext#getDefault() default data context}</li>
* <li>the {@link AbstractDetector#DEFAULT_MAXCHECK default value} for maximal checking interval</li>
* <li>the {@link AbstractDetector#DEFAULT_THRESHOLD default value} for convergence threshold</li>
* <li>the <code>atSeaLevel</code> switch set to false</li>
* </ul>
*
* @param limit threshold value for magnetic field detection, in Teslas
* @param model magnetic field model
* @param body Earth body shape
* @see #MagneticFieldDetector(double, double, double, GeoMagneticFieldFactory.FieldModel, OneAxisEllipsoid, boolean, DataContext)
*/
@DefaultDataContext
public MagneticFieldDetector(final double limit, final FieldModel model, final OneAxisEllipsoid body) {
this(DEFAULT_MAXCHECK, DEFAULT_THRESHOLD, limit, model, body, false);
}
/** Build a new detector.
*
* <p>This constructor uses:
* <ul>
* <li>the {@link DataContext#getDefault() default data context}</li>
* <li>the {@link AbstractDetector#DEFAULT_MAXCHECK default value} for maximal checking interval</li>
* <li>the {@link AbstractDetector#DEFAULT_THRESHOLD default value} for convergence threshold </li>
* </ul>
*
* @param limit threshold value for magnetic field detection, in Teslas
* @param model magnetic field model
* @param body Earth body shape
* @param atSeaLevel switch for calculating field intensity at sea level (true) or satellite altitude (false)
* @see #MagneticFieldDetector(double, double, double, GeoMagneticFieldFactory.FieldModel, OneAxisEllipsoid, boolean, DataContext)
*/
@DefaultDataContext
public MagneticFieldDetector(final double limit, final FieldModel model,
final OneAxisEllipsoid body, final boolean atSeaLevel) {
this(DEFAULT_MAXCHECK, DEFAULT_THRESHOLD, limit, model, body, atSeaLevel);
}
/** Build a detector.
*
* <p>This method uses the {@link DataContext#getDefault() default data context}.</p>
*
* @param maxCheck maximal checking interval (s)
* @param threshold convergence threshold (s)
* @param limit threshold value for magnetic field detection, in Teslas
* @param model magnetic field model
* @param body Earth body shape
* @param atSeaLevel switch for calculating field intensity at sea level (true) or satellite altitude (false)
* @see #MagneticFieldDetector(double, double, double, GeoMagneticFieldFactory.FieldModel, OneAxisEllipsoid, boolean, DataContext)
*/
@DefaultDataContext
public MagneticFieldDetector(final double maxCheck, final double threshold, final double limit,
final FieldModel model, final OneAxisEllipsoid body, final boolean atSeaLevel) {
this(maxCheck, threshold, limit, model, body, atSeaLevel, DataContext.getDefault());
}
/**
* Build a detector.
*
* @param maxCheck maximal checking interval (s)
* @param threshold convergence threshold (s)
* @param limit threshold value for magnetic field detection, in Teslas
* @param model magnetic field model
* @param body Earth body shape
* @param atSeaLevel switch for calculating field intensity at sea level (true) or satellite altitude (false)
* @param dataContext used to look up the magnetic field model.
* @since 10.1
*/
public MagneticFieldDetector(final double maxCheck,
final double threshold,
final double limit,
final FieldModel model,
final OneAxisEllipsoid body,
final boolean atSeaLevel,
final DataContext dataContext) {
this(AdaptableInterval.of(maxCheck), threshold, DEFAULT_MAX_ITER, new StopOnIncreasing(),
limit, model, body, atSeaLevel, dataContext);
}
/** 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 maximal 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 limit threshold value for magnetic field detection, in Teslas
* @param model magnetic field model
* @param body Earth body shape
* @param atSeaLevel switch for calculating field intensity at sea level (true) or satellite altitude (false)
* @param dataContext used to look up the magnetic field model.
*/
protected MagneticFieldDetector(final AdaptableInterval maxCheck, final double threshold,
final int maxIter, final EventHandler handler,
final double limit, final FieldModel model, final OneAxisEllipsoid body,
final boolean atSeaLevel, final DataContext dataContext) {
super(new EventDetectionSettings(maxCheck, threshold, maxIter), handler);
this.limit = limit;
this.model = model;
this.body = body;
this.atSeaLevel = atSeaLevel;
this.dataContext = dataContext;
}
/** {@inheritDoc} */
@Override
protected MagneticFieldDetector create(final AdaptableInterval newMaxCheck, final double newThreshold,
final int newMaxIter, final EventHandler newHandler) {
return new MagneticFieldDetector(newMaxCheck, newThreshold, newMaxIter, newHandler,
limit, model, body, atSeaLevel, dataContext);
}
/** {@inheritDoc} */
@Override
public void init(final SpacecraftState s0, final AbsoluteDate t) {
super.init(s0, t);
final TimeScale utc = dataContext.getTimeScales().getUTC();
this.currentYear = s0.getDate().getComponents(utc).getDate().getYear();
this.field = dataContext.getGeoMagneticFields().getField(model, currentYear);
}
/** Compute the value of the detection function.
* <p>
* The returned value is the difference between the field intensity at spacecraft location,
* taking <code>atSeaLevel</code> switch into account, and the fixed threshold value.
* </p>
* @param s the current state information: date, kinematics, attitude
* @return difference between the field intensity at spacecraft location
* and the fixed threshold value
*/
public double g(final SpacecraftState s) {
final TimeScale utc = dataContext.getTimeScales().getUTC();
if (s.getDate().getComponents(utc).getDate().getYear() != currentYear) {
this.currentYear = s.getDate().getComponents(utc).getDate().getYear();
this.field = dataContext.getGeoMagneticFields().getField(model, currentYear);
}
final GeodeticPoint geoPoint = body.transform(s.getPosition(), s.getFrame(), s.getDate());
final double altitude = atSeaLevel ? 0. : geoPoint.getAltitude();
final double value = field.calculateField(geoPoint.getLatitude(), geoPoint.getLongitude(), altitude).getTotalIntensity();
return value - limit;
}
}