LongitudeRangeCrossingDetector.java
/* Copyright 2023-2024 Alberto Ferrero
* Licensed to CS GROUP (CS) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* Alberto Ferrero licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* 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.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.orekit.propagation.events;
import org.hipparchus.util.FastMath;
import org.orekit.bodies.GeodeticPoint;
import org.orekit.bodies.OneAxisEllipsoid;
import org.orekit.propagation.SpacecraftState;
import org.orekit.propagation.events.handlers.EventHandler;
import org.orekit.propagation.events.handlers.StopOnDecreasing;
/** Detector for geographic longitude crossing.
* <p>This detector identifies when a spacecraft crosses a fixed
* longitude range with respect to a central body.</p>
* @author Alberto Ferrero
* @since 12.0
*/
public class LongitudeRangeCrossingDetector extends AbstractDetector<LongitudeRangeCrossingDetector> {
/** Body on which the longitude is defined. */
private final OneAxisEllipsoid body;
/** Fixed longitude to be crossed, lower boundary in radians. */
private final double fromLongitude;
/** Fixed longitude to be crossed, upper boundary in radians. */
private final double toLongitude;
/**
* Sign, to get reversed inclusion longitude range (lower > upper).
*/
private final double sign;
/** 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 longitude is defined
* @param fromLongitude longitude to be crossed, lower range boundary
* @param toLongitude longitude to be crossed, upper range boundary
*/
public LongitudeRangeCrossingDetector(final OneAxisEllipsoid body, final double fromLongitude, final double toLongitude) {
this(DEFAULT_MAXCHECK, DEFAULT_THRESHOLD, body, fromLongitude, toLongitude);
}
/** Build a detector.
* @param maxCheck maximal checking interval (s)
* @param threshold convergence threshold (s)
* @param body body on which the longitude is defined
* @param fromLongitude longitude to be crossed, lower range boundary
* @param toLongitude longitude to be crossed, upper range boundary
*/
public LongitudeRangeCrossingDetector(final double maxCheck, final double threshold,
final OneAxisEllipsoid body, final double fromLongitude, final double toLongitude) {
this(AdaptableInterval.of(maxCheck), threshold, DEFAULT_MAX_ITER, new StopOnDecreasing(),
body, fromLongitude, toLongitude);
}
/** 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 longitude is defined
* @param fromLongitude longitude to be crossed, lower range boundary
* @param toLongitude longitude to be crossed, upper range boundary
*/
protected LongitudeRangeCrossingDetector(final AdaptableInterval maxCheck, final double threshold, final int maxIter,
final EventHandler handler,
final OneAxisEllipsoid body, final double fromLongitude, final double toLongitude) {
super(maxCheck, threshold, maxIter, handler);
this.body = body;
this.fromLongitude = ensureLongitudePositiveContinuity(fromLongitude);
this.toLongitude = ensureLongitudePositiveContinuity(toLongitude);
this.sign = FastMath.signum(this.toLongitude - this.fromLongitude);
}
/** {@inheritDoc} */
@Override
protected LongitudeRangeCrossingDetector create(final AdaptableInterval newMaxCheck,
final double newThreshold,
final int newMaxIter,
final EventHandler newHandler) {
return new LongitudeRangeCrossingDetector(newMaxCheck, newThreshold, newMaxIter, newHandler,
body, fromLongitude, toLongitude);
}
/** Get the body on which the geographic zone is defined.
* @return body on which the geographic zone is defined
*/
public OneAxisEllipsoid getBody() {
return body;
}
/** Get the fixed longitude range to be crossed (radians), lower boundary.
* @return fixed lower boundary longitude range to be crossed (radians)
*/
public double getFromLongitude() {
return getLongitudeOverOriginalRange(fromLongitude);
}
/** Get the fixed longitude range to be crossed (radians), upper boundary.
* @return fixed upper boundary longitude range to be crossed (radians)
*/
public double getToLongitude() {
return getLongitudeOverOriginalRange(toLongitude);
}
/**
* Ensure continuity for negative angles, as longitude defined as [-PI, PI], transform negative to positive.
* New longitude angle definition from [0, 2 PI].
* @param longitude original longitude value
* @return positive range longitude
*/
private double ensureLongitudePositiveContinuity(final double longitude) {
return longitude < 0 ? longitude + 2 * FastMath.PI : longitude;
}
/**
* Get longitude shifted over the original range [-PI, PI].
* @param longitude longitude value to convert
* @return original range longitude
*/
private double getLongitudeOverOriginalRange(final double longitude) {
return longitude > FastMath.PI ? longitude - 2 * FastMath.PI : longitude;
}
/** Compute the value of the detection function.
* <p>
* The value is positive if the spacecraft longitude is inside the longitude range.
* The longitude value is reflected from [-PI, +PI] to [0, 2 PI] to ensure continuity.
* </p>
* @param s the current state information: date, kinematics, attitude
* @return positive if spacecraft inside the range
*/
public double g(final SpacecraftState s) {
// convert state to geodetic coordinates
final GeodeticPoint gp = body.transform(s.getPVCoordinates().getPosition(),
s.getFrame(), s.getDate());
// point longitude
final double longitude = ensureLongitudePositiveContinuity(gp.getLongitude());
// inside or outside longitude range
return sign * (longitude - fromLongitude) * (toLongitude - longitude);
}
}