/* Copyright 2002-2017 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.analysis.differentiation.DerivativeStructure;
import org.hipparchus.geometry.euclidean.threed.FieldVector3D;
import org.orekit.errors.OrekitException;
import org.orekit.frames.TopocentricFrame;
import org.orekit.frames.Transform;
import org.orekit.propagation.SpacecraftState;
import org.orekit.propagation.events.handlers.EventHandler;
import org.orekit.propagation.events.handlers.StopOnIncreasing;
import org.orekit.utils.TimeStampedPVCoordinates;
/** Detector for elevation extremum with respect to a ground point.
* <p>This detector identifies when a spacecraft reaches its
* extremum elevation with respect to a ground point.</p>
* <p>
* As in most cases only the elevation maximum is needed and the
* minimum is often irrelevant, this detector is often wrapped into
* an {@link EventSlopeFilter event slope filter} configured with
* {@link FilterType#TRIGGER_ONLY_DECREASING_EVENTS} (i.e. when the
* elevation derivative decreases from positive values to negative values,
* which correspond to a maximum). Setting up this filter saves some computation
* time as the elevation minimum occurrences are not even looked at. It is
* however still often necessary to do an additional filtering
* </p>
* @author Luc Maisonobe
* @since 7.1
*/
public class ElevationExtremumDetector extends AbstractDetector<ElevationExtremumDetector> {
/** Serializable UID. */
private static final long serialVersionUID = 20150909L;
/** Topocentric frame in which elevation should be evaluated. */
private final TopocentricFrame topo;
/** 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 topo topocentric frame centered on ground point
*/
public ElevationExtremumDetector(final TopocentricFrame topo) {
this(DEFAULT_MAXCHECK, DEFAULT_THRESHOLD, topo);
}
/** Build a detector.
* @param maxCheck maximal checking interval (s)
* @param threshold convergence threshold (s)
* @param topo topocentric frame centered on ground point
*/
public ElevationExtremumDetector(final double maxCheck, final double threshold,
final TopocentricFrame topo) {
this(maxCheck, threshold, DEFAULT_MAX_ITER, new StopOnIncreasing<ElevationExtremumDetector>(),
topo);
}
/** 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 topo topocentric frame centered on ground point
*/
private ElevationExtremumDetector(final double maxCheck, final double threshold,
final int maxIter, final EventHandler<? super ElevationExtremumDetector> handler,
final TopocentricFrame topo) {
super(maxCheck, threshold, maxIter, handler);
this.topo = topo;
}
/** {@inheritDoc} */
@Override
protected ElevationExtremumDetector create(final double newMaxCheck, final double newThreshold,
final int newMaxIter,
final EventHandler<? super ElevationExtremumDetector> newHandler) {
return new ElevationExtremumDetector(newMaxCheck, newThreshold, newMaxIter, newHandler, topo);
}
/**
* Returns the topocentric frame centered on ground point.
* @return topocentric frame centered on ground point
*/
public TopocentricFrame getTopocentricFrame() {
return this.topo;
}
/** Get the elevation value.
* @param s the current state information: date, kinematics, attitude
* @return spacecraft elevation
* @exception OrekitException if some specific error occurs
*/
public double getElevation(final SpacecraftState s) throws OrekitException {
return topo.getElevation(s.getPVCoordinates().getPosition(), s.getFrame(), s.getDate());
}
/** Compute the value of the detection function.
* <p>
* The value is the spacecraft elevation first time derivative.
* </p>
* @param s the current state information: date, kinematics, attitude
* @return spacecraft elevation first time derivative
* @exception OrekitException if some specific error occurs
*/
public double g(final SpacecraftState s) throws OrekitException {
// get position, velocity acceleration of spacecraft in topocentric frame
final Transform inertToTopo = s.getFrame().getTransformTo(topo, s.getDate());
final TimeStampedPVCoordinates pvTopo = inertToTopo.transformPVCoordinates(s.getPVCoordinates());
// convert the coordinates to DerivativeStructure based vector
// instead of having vector position, then vector velocity then vector acceleration
// we get one vector and each coordinate is a DerivativeStructure containing
// value, first time derivative (we don't need second time derivative here)
final FieldVector3D<DerivativeStructure> pvDS = pvTopo.toDerivativeStructureVector(1);
// compute elevation and its first time derivative
final DerivativeStructure elevation = pvDS.getZ().divide(pvDS.getNorm()).asin();
// return elevation first time derivative
return elevation.getPartialDerivative(1);
}
}