MagneticFieldDetector.java
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* Unless required by applicable law or agreed to in writing, software
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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.errors.OrekitIllegalArgumentException;
import org.orekit.models.earth.GeoMagneticField;
import org.orekit.models.earth.GeoMagneticFieldFactory.FieldModel;
import org.orekit.orbits.OrbitType;
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 South-Atlantic anomaly frontier crossing.
* <p>
* The detector is based on the value of the earth magnetic field at see level at the satellite latitude and longitude.
* </p>
* @author Romaric Her
*/
public class MagneticFieldDetector extends AbstractDetector<MagneticFieldDetector> {
/** Fixed threshold value of Magnetic field to be crossed. */
private final double limit;
/** Fixed altitude of computed magnetic field value. */
private final boolean seaLevel;
/** earth geomagnetic field. */
private GeoMagneticField field;
/** year of the current state. */
private double currentYear;
/** the geomagnetic field model enum. */
private final FieldModel type;
/** the body. */
private final OneAxisEllipsoid body;
/** the timescale. */
private final DataContext dataContext;
/** Build a new detector.
* <p>The new instance uses default values for maximal checking interval
* ({@link #DEFAULT_MAXCHECK}) and convergence threshold ({@link
* #DEFAULT_THRESHOLD}).</p>
*
* <p>This method uses the {@link DataContext#getDefault() default data context}.
*
* @param limit the threshold value of magnetic field at see level
* @param type the magnetic field model
* @param body the body
* @exception OrekitIllegalArgumentException if orbit type is {@link OrbitType#CARTESIAN}
* @see #MagneticFieldDetector(double, double, double, GeoMagneticFieldFactory.FieldModel, OneAxisEllipsoid, boolean, DataContext)
*/
@DefaultDataContext
public MagneticFieldDetector(final double limit, final FieldModel type, final OneAxisEllipsoid body)
throws OrekitIllegalArgumentException {
this(DEFAULT_MAXCHECK, DEFAULT_THRESHOLD, limit, type, body, false);
}
/** Build a new detector.
* <p>The new instance uses default values for maximal checking interval
* ({@link #DEFAULT_MAXCHECK}) and convergence threshold ({@link
* #DEFAULT_THRESHOLD}).</p>
*
* <p>This method uses the {@link DataContext#getDefault() default data context}.
*
* @param limit the threshold value of magnetic field at see level
* @param type the magnetic field model
* @param body the body
* @param seaLevel true if the magnetic field intensity is computed at the sea level, false if it is computed at satellite altitude
* @exception OrekitIllegalArgumentException if orbit type is {@link OrbitType#CARTESIAN}
* @see #MagneticFieldDetector(double, double, double, GeoMagneticFieldFactory.FieldModel, OneAxisEllipsoid, boolean, DataContext)
*/
@DefaultDataContext
public MagneticFieldDetector(final double limit, final FieldModel type, final OneAxisEllipsoid body, final boolean seaLevel)
throws OrekitIllegalArgumentException {
this(DEFAULT_MAXCHECK, DEFAULT_THRESHOLD, limit, type, body, seaLevel);
}
/** Build a detector.
*
* <p>This method uses the {@link DataContext#getDefault() default data context}.
*
* @param maxCheck maximal checking interval (s)
* @param threshold convergence threshold (s)
* @param limit the threshold value of magnetic field at see level
* @param type the magnetic field model
* @param body the body
* @param seaLevel true if the magnetic field intensity is computed at the sea level, false if it is computed at satellite altitude
* @exception OrekitIllegalArgumentException if orbit type is {@link OrbitType#CARTESIAN}
* @see #MagneticFieldDetector(double, double, double, GeoMagneticFieldFactory.FieldModel, OneAxisEllipsoid, boolean, DataContext)
*/
@DefaultDataContext
public MagneticFieldDetector(final double maxCheck, final double threshold, final double limit,
final FieldModel type, final OneAxisEllipsoid body, final boolean seaLevel)
throws OrekitIllegalArgumentException {
this(maxCheck, threshold, limit, type, body, seaLevel,
DataContext.getDefault());
}
/**
* Build a detector.
*
* @param maxCheck maximal checking interval (s)
* @param threshold convergence threshold (s)
* @param limit the threshold value of magnetic field at see level
* @param type the magnetic field model
* @param body the body
* @param seaLevel true if the magnetic field intensity is computed at the sea
* level, false if it is computed at satellite altitude
* @param dataContext used to look up the magnetic field model.
* @throws OrekitIllegalArgumentException if orbit type is {@link OrbitType#CARTESIAN}
* @since 10.1
*/
public MagneticFieldDetector(final double maxCheck,
final double threshold,
final double limit,
final FieldModel type,
final OneAxisEllipsoid body,
final boolean seaLevel,
final DataContext dataContext)
throws OrekitIllegalArgumentException {
this(maxCheck, threshold, DEFAULT_MAX_ITER, new StopOnIncreasing<>(),
limit, type, body, seaLevel, dataContext);
}
/** Private constructor with full parameters.
* <p>
* This constructor is private 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 (s)
* @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 the threshold value of magnetic field at see level
* @param type the magnetic field model
* @param body the body
* @param seaLevel true if the magnetic field intensity is computed at the sea level, false if it is computed at satellite altitude
* @param dataContext used to look up the magnetic field model.
* @exception OrekitIllegalArgumentException if orbit type is {@link OrbitType#CARTESIAN}
*/
private MagneticFieldDetector(final double maxCheck, final double threshold,
final int maxIter, final EventHandler<? super MagneticFieldDetector> handler,
final double limit, final FieldModel type, final OneAxisEllipsoid body, final boolean seaLevel,
final DataContext dataContext)
throws OrekitIllegalArgumentException {
super(maxCheck, threshold, maxIter, handler);
this.limit = limit;
this.type = type;
this.body = body;
this.seaLevel = seaLevel;
this.dataContext = dataContext;
}
/** {@inheritDoc} */
@Override
protected MagneticFieldDetector create(final double newMaxCheck, final double newThreshold,
final int newMaxIter, final EventHandler<? super MagneticFieldDetector> newHandler) {
return new MagneticFieldDetector(newMaxCheck, newThreshold, newMaxIter, newHandler,
limit, type, body, seaLevel, dataContext);
}
/** {@inheritDoc} */
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(type, currentYear);
}
/** Compute the value of the detection function.
* <p>
* The value is the angle difference between the spacecraft and the fixed
* angle to be crossed, with some sign tweaks to ensure continuity.
* These tweaks imply the {@code increasing} flag in events detection becomes
* irrelevant here! As an example, the angle always increase in a Keplerian
* orbit, but this g function will increase and decrease so it
* will cross the zero value once per orbit, in increasing and decreasing
* directions on alternate orbits..
* </p>
* @param s the current state information: date, kinematics, attitude
* @return angle difference between the spacecraft and the fixed
* angle, with some sign tweaks to ensure continuity
*/
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(type, currentYear);
}
final GeodeticPoint geoPoint = body.transform(s.getPVCoordinates().getPosition(), s.getFrame(), s.getDate());
final double altitude;
if (seaLevel) {
altitude = 0;
}
else {
altitude = geoPoint.getAltitude();
}
final double value = field.calculateField(geoPoint.getLatitude(), geoPoint.getLongitude(), altitude).getTotalIntensity();
return value - limit;
}
}