GeographicZoneDetector.java
/* Copyright 2002-2015 CS Systèmes d'Information
* Licensed to CS Systèmes d'Information (CS) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* CS licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
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*
* http://www.apache.org/licenses/LICENSE-2.0
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* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* limitations under the License.
*/
package org.orekit.propagation.events;
import java.io.Serializable;
import org.apache.commons.math3.geometry.enclosing.EnclosingBall;
import org.apache.commons.math3.geometry.euclidean.threed.Vector3D;
import org.apache.commons.math3.geometry.partitioning.BSPTree;
import org.apache.commons.math3.geometry.partitioning.BSPTreeVisitor;
import org.apache.commons.math3.geometry.spherical.twod.Circle;
import org.apache.commons.math3.geometry.spherical.twod.S2Point;
import org.apache.commons.math3.geometry.spherical.twod.Sphere2D;
import org.apache.commons.math3.geometry.spherical.twod.SphericalPolygonsSet;
import org.apache.commons.math3.util.FastMath;
import org.orekit.bodies.BodyShape;
import org.orekit.bodies.GeodeticPoint;
import org.orekit.errors.OrekitException;
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>
* @author Luc Maisonobe
* @since 6.2
*/
public class GeographicZoneDetector extends AbstractDetector<GeographicZoneDetector> {
/** Serializable UID. */
private static final long serialVersionUID = 20140619L;
/** Body on which the geographic zone is defined. */
private BodyShape body;
/** Zone definition. */
private final transient SphericalPolygonsSet zone;
/** Spherical cap surrounding the zone. */
private final transient 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(maxCheck, threshold, DEFAULT_MAX_ITER, new StopOnIncreasing<GeographicZoneDetector>(),
body, zone, zone.getEnclosingCap(), margin);
}
/** 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 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
*/
private GeographicZoneDetector(final double maxCheck, final double threshold,
final int maxIter, final EventHandler<GeographicZoneDetector> handler,
final BodyShape body,
final SphericalPolygonsSet zone,
final EnclosingBall<Sphere2D, S2Point> cap,
final double margin) {
super(maxCheck, threshold, maxIter, handler);
this.body = body;
this.zone = zone;
this.cap = cap;
this.margin = margin;
}
/** {@inheritDoc} */
@Override
protected GeographicZoneDetector create(final double newMaxCheck, final double newThreshold,
final int newMaxIter, final EventHandler<GeographicZoneDetector> newHandler) {
return new GeographicZoneDetector(newMaxCheck, newThreshold, newMaxIter, 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(getMaxCheckInterval(), getThreshold(), getMaxIterationCount(), 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
* @exception OrekitException if some specific error occurs
*/
public double g(final SpacecraftState s) throws OrekitException {
// convert state to geodetic coordinates
final GeodeticPoint gp = body.transform(s.getPVCoordinates().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;
}
/** Replace the instance with a data transfer object for serialization.
* @return data transfer object that will be serialized
*/
private Object writeReplace() {
return new DTO(this);
}
/** Internal class used only for serialization. */
private static class DTO implements Serializable {
/** Serializable UID. */
private static final long serialVersionUID = 20140619L;
/** Max check interval. */
private final double maxCheck;
/** Convergence threshold. */
private final double threshold;
/** Maximum number of iterations in the event time search. */
private final int maxIter;
/** Body on which the geographic zone is defined. */
private final BodyShape body;
/** Margin to apply to the zone. */
private final double margin;
/** Tolerance for the zone. */
private final double tolerance;
/** Zone cut hyperplanes. */
private final double[] cuts;
/** Leaf nodes indices. */
private final int[] leafs;
/** Zone interior/exterior indicators. */
private final boolean[] flags;
/** Internal nodes counter. */
private transient int internalNodes;
/** Leaf nodes counter. */
private transient int leafNodes;
/** Node index. */
private transient int nodeIndex;
/** Index in cut hyperplanes array. */
private transient int cutIndex;
/** Index in interior/exterior flags array. */
private transient int flagIndex;
/** Simple constructor.
* @param detector instance to serialize
*/
private DTO(final GeographicZoneDetector detector) {
this.maxCheck = detector.getMaxCheckInterval();
this.threshold = detector.getThreshold();
this.maxIter = detector.getMaxIterationCount();
this.body = detector.body;
this.margin = detector.margin;
this.tolerance = detector.zone.getTolerance();
// count the nodes
internalNodes = 0;
leafNodes = 0;
detector.zone.getTree(false).visit(new BSPTreeVisitor<Sphere2D>() {
/** {@inheritDoc} */
public Order visitOrder(final BSPTree<Sphere2D> node) {
return Order.SUB_MINUS_PLUS;
}
/** {@inheritDoc} */
public void visitInternalNode(final BSPTree<Sphere2D> node) {
++internalNodes;
}
/** {@inheritDoc} */
public void visitLeafNode(final BSPTree<Sphere2D> node) {
++leafNodes;
}
});
// allocate the arrays for flattened tree
cuts = new double[3 * internalNodes];
leafs = new int[leafNodes];
flags = new boolean[leafNodes];
nodeIndex = 0;
cutIndex = 0;
flagIndex = 0;
detector.zone.getTree(false).visit(new BSPTreeVisitor<Sphere2D>() {
/** {@inheritDoc} */
public Order visitOrder(final BSPTree<Sphere2D> node) {
return Order.SUB_MINUS_PLUS;
}
/** {@inheritDoc} */
public void visitInternalNode(final BSPTree<Sphere2D> node) {
final Vector3D cutPole = ((Circle) node.getCut().getHyperplane()).getPole();
cuts[cutIndex++] = cutPole.getX();
cuts[cutIndex++] = cutPole.getY();
cuts[cutIndex++] = cutPole.getZ();
nodeIndex++;
}
/** {@inheritDoc} */
public void visitLeafNode(final BSPTree<Sphere2D> node) {
leafs[flagIndex] = nodeIndex++;
flags[flagIndex++] = (Boolean) node.getAttribute();
}
});
}
/** Replace the deserialized data transfer object with a {@link GeographicZoneDetector}.
* @return replacement {@link GeographicZoneDetector}
*/
private Object readResolve() {
// rebuild the tree from the flattened arrays
BSPTree<Sphere2D> node = new BSPTree<Sphere2D>();
final int nbNodes = cuts.length / 3 + leafs.length;
cutIndex = 0;
flagIndex = 0;
for (nodeIndex = 0; nodeIndex < nbNodes; ++nodeIndex) {
if (leafs[flagIndex] == nodeIndex) {
// this is a leaf node
node.setAttribute(Boolean.valueOf(flags[flagIndex++]));
while (node.getParent() != null) {
final BSPTree<Sphere2D> parent = node.getParent();
if (node == parent.getMinus()) {
node = parent.getPlus();
break;
} else {
node = parent;
}
}
} else {
// this is an internal node
final double x = cuts[cutIndex++];
final double y = cuts[cutIndex++];
final double z = cuts[cutIndex++];
node.insertCut(new Circle(new Vector3D(x, y, z), tolerance));
node = node.getMinus();
}
}
return new GeographicZoneDetector(body, new SphericalPolygonsSet(node, tolerance), margin).
withMaxCheck(maxCheck).
withThreshold(threshold).
withMaxIter(maxIter);
}
}
}