GeographicZoneDetector.java
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package org.orekit.propagation.events;
import org.hipparchus.geometry.enclosing.EnclosingBall;
import org.hipparchus.geometry.spherical.twod.S2Point;
import org.hipparchus.geometry.spherical.twod.Sphere2D;
import org.hipparchus.geometry.spherical.twod.SphericalPolygonsSet;
import org.hipparchus.util.FastMath;
import org.orekit.bodies.BodyShape;
import org.orekit.bodies.GeodeticPoint;
import org.orekit.propagation.SpacecraftState;
import org.orekit.propagation.events.handlers.EventHandler;
import org.orekit.propagation.events.handlers.StopOnIncreasing;
/** Detector for entry/exit of a zone defined by geographic boundaries.
* <p>This detector identifies when a spacecraft crosses boundaries of
* general shapes defined on the surface of the globe. Typical shapes
* of interest can be countries, land masses or physical areas like
* the south atlantic anomaly. Shapes can be arbitrarily complicated:
* convex or non-convex, in one piece or several non-connected islands,
* they can include poles, they can have holes like the Caspian Sea (this
* would be a hole only if one is interested in land masses, of course).
* Complex shapes involve of course more computing time than simple shapes.</p>
* @see FootprintOverlapDetector
* @author Luc Maisonobe
* @since 6.2
*/
public class GeographicZoneDetector extends AbstractDetector<GeographicZoneDetector> {
/** Body on which the geographic zone is defined. */
private BodyShape body;
/** Zone definition. */
private final SphericalPolygonsSet zone;
/** Spherical cap surrounding the zone. */
private final EnclosingBall<Sphere2D, S2Point> cap;
/** Margin to apply to the zone. */
private final double margin;
/** 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>
* @param body body on which the geographic zone is defined
* @param zone geographic zone to consider
* @param margin angular margin to apply to the zone
*/
public GeographicZoneDetector(final BodyShape body,
final SphericalPolygonsSet zone, final double margin) {
this(DEFAULT_MAXCHECK, DEFAULT_THRESHOLD, body, zone, margin);
}
/** Build a detector.
* @param maxCheck maximal checking interval (s)
* @param threshold convergence threshold (s)
* @param body body on which the geographic zone is defined
* @param zone geographic zone to consider
* @param margin angular margin to apply to the zone
*/
public GeographicZoneDetector(final double maxCheck, final double threshold,
final BodyShape body,
final SphericalPolygonsSet zone, final double margin) {
this(new EventDetectionSettings(maxCheck, threshold, DEFAULT_MAX_ITER), new StopOnIncreasing(),
body, zone, zone.getEnclosingCap(), margin);
}
/** 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 detectionSettings event detection settings
* @param handler event handler to call at event occurrences
* @param body body on which the geographic zone is defined
* @param zone geographic zone to consider
* @param cap spherical cap surrounding the zone
* @param margin angular margin to apply to the zone
* @since 13.0
*/
protected GeographicZoneDetector(final EventDetectionSettings detectionSettings, final EventHandler handler,
final BodyShape body,
final SphericalPolygonsSet zone,
final EnclosingBall<Sphere2D, S2Point> cap,
final double margin) {
super(detectionSettings, handler);
this.body = body;
this.zone = zone;
this.cap = cap;
this.margin = margin;
}
/** {@inheritDoc} */
@Override
protected GeographicZoneDetector create(final EventDetectionSettings detectionSettings, final EventHandler newHandler) {
return new GeographicZoneDetector(detectionSettings, newHandler,
body, zone, cap, margin);
}
/**
* Setup the detector margin.
* @param newMargin angular margin to apply to the zone
* @return a new detector with updated configuration (the instance is not changed)
*/
public GeographicZoneDetector withMargin(final double newMargin) {
return new GeographicZoneDetector(getDetectionSettings(), getHandler(), body, zone, cap, newMargin);
}
/** Get the body on which the geographic zone is defined.
* @return body on which the geographic zone is defined
*/
public BodyShape getBody() {
return body;
}
/** Get the geographic zone.
* @return the geographic zone
*/
public SphericalPolygonsSet getZone() {
return zone;
}
/** Get the angular margin to apply (radians).
* @return the angular margin to apply (radians)
*/
public double getMargin() {
return margin;
}
/** Compute the value of the detection function.
* <p>
* The value is the signed distance to boundary, minus the margin. It is
* positive if the spacecraft is outside of the zone and negative if it is inside.
* </p>
* @param s the current state information: date, kinematics, attitude
* @return signed distance to boundary minus the margin
*/
public double g(final SpacecraftState s) {
// convert state to geodetic coordinates
final GeodeticPoint gp = body.transform(s.getPosition(),
s.getFrame(), s.getDate());
// map the point to a sphere (geodetic coordinates have already taken care of ellipsoid flatness)
final S2Point s2p = new S2Point(gp.getLongitude(), 0.5 * FastMath.PI - gp.getLatitude());
// for faster computation, we start using only the surrounding cap, to filter out
// far away points (which correspond to most of the points if the zone is small)
final double crudeDistance = cap.getCenter().distance(s2p) - cap.getRadius();
if (crudeDistance - margin > FastMath.max(FastMath.abs(margin), 0.01)) {
// we know we are strictly outside of the zone,
// use the crude distance to compute the (positive) return value
return crudeDistance - margin;
}
// we are close, we need to compute carefully the exact offset
// project the point to the closest zone boundary
return zone.projectToBoundary(s2p).getOffset() - margin;
}
}