PositionAngleDetector.java
/* Copyright 2002-2018 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
* 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.hipparchus.util.MathUtils;
import org.orekit.errors.OrekitException;
import org.orekit.errors.OrekitIllegalArgumentException;
import org.orekit.errors.OrekitInternalError;
import org.orekit.errors.OrekitMessages;
import org.orekit.orbits.CircularOrbit;
import org.orekit.orbits.EquinoctialOrbit;
import org.orekit.orbits.KeplerianOrbit;
import org.orekit.orbits.OrbitType;
import org.orekit.orbits.PositionAngle;
import org.orekit.propagation.SpacecraftState;
import org.orekit.propagation.events.handlers.EventHandler;
import org.orekit.propagation.events.handlers.StopOnIncreasing;
/** Detector for in-orbit position angle.
* <p>
* The detector is based on anomaly for {@link OrbitType#KEPLERIAN Keplerian}
* orbits, latitude argument for {@link OrbitType#CIRCULAR circular} orbits,
* or longitude argument for {@link OrbitType#EQUINOCTIAL equinoctial} orbits.
* It does not support {@link OrbitType#CARTESIAN Cartesian} orbits. The
* angles can be either {@link PositionAngle#TRUE true}, {link {@link PositionAngle#MEAN
* mean} or {@link PositionAngle#ECCENTRIC eccentric} angles.
* </p>
* @author Luc Maisonobe
* @since 7.1
*/
public class PositionAngleDetector extends AbstractDetector<PositionAngleDetector> {
/** Serializable UID. */
private static final long serialVersionUID = 20150825L;
/** Orbit type defining the angle type. */
private final OrbitType orbitType;
/** Type of position angle. */
private final PositionAngle positionAngle;
/** Fixed angle to be crossed. */
private final double angle;
/** Sign to apply for angle difference. */
private double sign;
/** Previous angle difference. */
private double previousDelta;
/** 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 orbitType orbit type defining the angle type
* @param positionAngle type of position angle
* @param angle fixed angle to be crossed
* @exception OrekitIllegalArgumentException if orbit type is {@link OrbitType#CARTESIAN}
*/
public PositionAngleDetector(final OrbitType orbitType, final PositionAngle positionAngle,
final double angle)
throws OrekitIllegalArgumentException {
this(DEFAULT_MAXCHECK, DEFAULT_THRESHOLD, orbitType, positionAngle, angle);
}
/** Build a detector.
* @param maxCheck maximal checking interval (s)
* @param threshold convergence threshold (s)
* @param orbitType orbit type defining the angle type
* @param positionAngle type of position angle
* @param angle fixed angle to be crossed
* @exception OrekitIllegalArgumentException if orbit type is {@link OrbitType#CARTESIAN}
*/
public PositionAngleDetector(final double maxCheck, final double threshold,
final OrbitType orbitType, final PositionAngle positionAngle,
final double angle)
throws OrekitIllegalArgumentException {
this(maxCheck, threshold, DEFAULT_MAX_ITER, new StopOnIncreasing<PositionAngleDetector>(),
orbitType, positionAngle, angle);
}
/** 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 orbitType orbit type defining the angle type
* @param positionAngle type of position angle
* @param angle fixed angle to be crossed
* @exception OrekitIllegalArgumentException if orbit type is {@link OrbitType#CARTESIAN}
*/
private PositionAngleDetector(final double maxCheck, final double threshold,
final int maxIter, final EventHandler<? super PositionAngleDetector> handler,
final OrbitType orbitType, final PositionAngle positionAngle,
final double angle)
throws OrekitIllegalArgumentException {
super(maxCheck, threshold, maxIter, handler);
if (orbitType == OrbitType.CARTESIAN) {
final String sep = ", ";
throw new OrekitIllegalArgumentException(OrekitMessages.ORBIT_TYPE_NOT_ALLOWED,
orbitType,
OrbitType.KEPLERIAN + sep +
OrbitType.CIRCULAR + sep +
OrbitType.EQUINOCTIAL);
}
this.orbitType = orbitType;
this.positionAngle = positionAngle;
this.angle = angle;
this.sign = +1.0;
this.previousDelta = Double.NaN;
}
/** {@inheritDoc} */
@Override
protected PositionAngleDetector create(final double newMaxCheck, final double newThreshold,
final int newMaxIter,
final EventHandler<? super PositionAngleDetector> newHandler) {
return new PositionAngleDetector(newMaxCheck, newThreshold, newMaxIter, newHandler,
orbitType, positionAngle, angle);
}
/** Get the orbit type defining the angle type.
* @return orbit type defining the angle type
*/
public OrbitType getOrbitType() {
return orbitType;
}
/** Get the type of position angle.
* @return type of position angle
*/
public PositionAngle getPositionAngle() {
return positionAngle;
}
/** Get the fixed angle to be crossed (radians).
* @return fixed angle to be crossed (radians)
*/
public double getAngle() {
return angle;
}
/** 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
* @exception OrekitException if some specific error occurs
*/
public double g(final SpacecraftState s) throws OrekitException {
// get angle
final double currentAngle;
switch (orbitType) {
case KEPLERIAN:
currentAngle = ((KeplerianOrbit) orbitType.convertType(s.getOrbit())).getAnomaly(positionAngle);
break;
case CIRCULAR:
currentAngle = ((CircularOrbit) orbitType.convertType(s.getOrbit())).getAlpha(positionAngle);
break;
case EQUINOCTIAL:
currentAngle = ((EquinoctialOrbit) orbitType.convertType(s.getOrbit())).getL(positionAngle);
break;
default:
// this should never happen as type was checked at construction
throw new OrekitInternalError(null);
}
// angle difference
double delta = MathUtils.normalizeAngle(sign * (currentAngle - angle), 0.0);
// ensure continuity
if (FastMath.abs(delta - previousDelta) > FastMath.PI) {
sign = -sign;
delta = MathUtils.normalizeAngle(sign * (currentAngle - angle), 0.0);
}
previousDelta = delta;
return delta;
}
}