GroundAtNightDetector.java
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package org.orekit.propagation.events;
import org.hipparchus.geometry.euclidean.threed.Vector3D;
import org.hipparchus.util.FastMath;
import org.orekit.frames.Frame;
import org.orekit.frames.TopocentricFrame;
import org.orekit.models.AtmosphericRefractionModel;
import org.orekit.propagation.SpacecraftState;
import org.orekit.propagation.events.handlers.ContinueOnEvent;
import org.orekit.propagation.events.handlers.EventHandler;
import org.orekit.time.AbsoluteDate;
import org.orekit.utils.PVCoordinatesProvider;
/** Detector for ground location being at night.
* <p>
* This detector is mainly useful for scheduling optical measurements
* (either passive telescope observation of satellites against the stars background
* or active satellite laser ranging).
* </p>
* <p>
* The {@code g} function of this detector is positive when ground is at night
* (i.e. Sun is below dawn/dusk elevation angle).
* </p>
* @author Luc Maisonobe
* @since 9.3
*/
public class GroundAtNightDetector extends AbstractDetector<GroundAtNightDetector> {
/** Sun elevation at civil dawn/dusk (6° below horizon). */
public static final double CIVIL_DAWN_DUSK_ELEVATION = FastMath.toRadians(-6.0);
/** Sun elevation at nautical dawn/dusk (12° below horizon). */
public static final double NAUTICAL_DAWN_DUSK_ELEVATION = FastMath.toRadians(-12.0);
/** Sun elevation at astronomical dawn/dusk (18° below horizon). */
public static final double ASTRONOMICAL_DAWN_DUSK_ELEVATION = FastMath.toRadians(-18.0);
/** Ground location to check. */
private final TopocentricFrame groundLocation;
/** Provider for Sun position. */
private final PVCoordinatesProvider sun;
/** Sun elevation below which we consider night is dark enough. */
private final double dawnDuskElevation;
/** Atmospheric Model used for calculations, if defined. */
private final AtmosphericRefractionModel refractionModel;
/** Simple constructor.
* <p>
* Beware that {@link org.orekit.models.earth.EarthStandardAtmosphereRefraction Earth
* standard refraction model} does apply only for elevations above -2°. It is therefore
* not suitable for used with {@link #CIVIL_DAWN_DUSK_ELEVATION} (-6°), {@link
* #NAUTICAL_DAWN_DUSK_ELEVATION} (-12°) or {@link #ASTRONOMICAL_DAWN_DUSK_ELEVATION} (-18°).
* The {@link org.orekit.models.earth.EarthITU453AtmosphereRefraction ITU 453 refraction model}
* which can compute refraction at large negative elevations should be preferred.
* </p>
* @param groundLocation ground location to check
* @param sun provider for Sun position
* @param dawnDuskElevation Sun elevation below which we consider night is dark enough (rad)
* (typically {@link #ASTRONOMICAL_DAWN_DUSK_ELEVATION})
* @param refractionModel reference to refraction model (null if refraction should be ignored)
*/
public GroundAtNightDetector(final TopocentricFrame groundLocation, final PVCoordinatesProvider sun,
final double dawnDuskElevation,
final AtmosphericRefractionModel refractionModel) {
this(groundLocation, sun, dawnDuskElevation, refractionModel,
DEFAULT_MAXCHECK, DEFAULT_THRESHOLD, DEFAULT_MAX_ITER,
new ContinueOnEvent<>());
}
/** Private constructor.
* @param groundLocation ground location from which measurement is performed
* @param sun provider for Sun position
* @param dawnDuskElevation Sun elevation below which we consider night is dark enough (rad)
* (typically {@link #ASTRONOMICAL_DAWN_DUSK_ELEVATION})
* @param refractionModel reference to refraction model (null if refraction should be ignored),
* @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
*/
private GroundAtNightDetector(final TopocentricFrame groundLocation, final PVCoordinatesProvider sun,
final double dawnDuskElevation,
final AtmosphericRefractionModel refractionModel,
final double maxCheck,
final double threshold,
final int maxIter,
final EventHandler<? super GroundAtNightDetector> handler) {
super(maxCheck, threshold, maxIter, handler);
this.groundLocation = groundLocation;
this.sun = sun;
this.dawnDuskElevation = dawnDuskElevation;
this.refractionModel = refractionModel;
}
/** {@inheritDoc} */
@Override
protected GroundAtNightDetector create(final double newMaxCheck,
final double newThreshold,
final int newMaxIter,
final EventHandler<? super GroundAtNightDetector> newHandler) {
return new GroundAtNightDetector(groundLocation, sun, dawnDuskElevation, refractionModel,
newMaxCheck, newThreshold, newMaxIter, newHandler);
}
/** {@inheritDoc}
* <p>
* The {@code g} function of this detector is positive when ground is at night
* (i.e. Sun is below dawn/dusk elevation angle).
* </p>
* <p>
* This function only depends on date, not on the actual position of the spacecraft.
* </p>
*/
@Override
public double g(final SpacecraftState state) {
final AbsoluteDate date = state.getDate();
final Frame frame = state.getFrame();
final Vector3D position = sun.getPVCoordinates(date, frame).getPosition();
final double trueElevation = groundLocation.getElevation(position, frame, date);
final double calculatedElevation;
if (refractionModel != null) {
calculatedElevation = trueElevation + refractionModel.getRefraction(trueElevation);
} else {
calculatedElevation = trueElevation;
}
return dawnDuskElevation - calculatedElevation;
}
}