ApparentElevationDetector.java
/* Copyright 2002-2013 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.apache.commons.math3.util.FastMath;
import org.orekit.errors.OrekitException;
import org.orekit.frames.TopocentricFrame;
import org.orekit.propagation.SpacecraftState;
import org.orekit.propagation.events.handlers.EventHandler;
import org.orekit.propagation.events.handlers.StopOnDecreasing;
/** Finder for satellite apparent elevation events.
* <p>This class finds apparent elevation events (i.e. apparent satellite raising
* and setting from a terrestrial viewpoint).</p>
* <p>Apparent elevation is the sum of geometrical elevation and refraction angle,
* the latter is 0 at zenith, about 1 arcminute at 45°, and 34 arcminutes at the
* horizon for optical wavelengths.</p>
* <p>This event only makes sense for positive apparent elevation in the Earth environment
* and it is not suited for near zenithal detection, where the simple
* {@link ElevationDetector} fits better.</p>
* <p>Refraction angle is computed according to Saemundssen formula quoted by Meeus.
* For reference, see <b>Astronomical Algorithms</b> (1998), 2nd ed,
* (ISBN 0-943396-61-1), chap. 15.</p>
* <p>This formula is about 30 arcseconds of accuracy very close to the horizon, as
* variable atmospheric effects become very important.</p>
* <p>Local pressure and temperature can be set to correct refraction at the viewpoint.</p>
* <p>The default implementation behavior is to {@link
* org.orekit.propagation.events.handlers.EventHandler.Action#CONTINUE continue}
* propagation at raising and to {@link
* org.orekit.propagation.events.handlers.EventHandler.Action#STOP stop} propagation
* at setting. This can be changed by calling
* {@link #withHandler(EventHandler)} after construction.</p>
* @see org.orekit.propagation.Propagator#addEventDetector(EventDetector)
* @author Pascal Parraud
* @deprecated as of 6.1 replaced by {@link ElevationDetector}
*/
@Deprecated
public class ApparentElevationDetector extends AbstractReconfigurableDetector<ApparentElevationDetector> {
/** Default local pressure at viewpoint (Pa). */
public static final double DEFAULT_PRESSURE = 101000.0;
/** Default local temperature at viewpoint (K). */
public static final double DEFAULT_TEMPERATURE = 283.0;
/** Serializable UID. */
private static final long serialVersionUID = 20131118L;
/** Elevation min value to compute refraction (under the horizon). */
private static final double MIN_ELEVATION = -2.0;
/** Elevation max value to compute refraction (zenithal). */
private static final double MAX_ELEVATION = 89.89;
/** Local pressure. */
private double pressure = DEFAULT_PRESSURE;
/** Local temperature. */
private double temperature = DEFAULT_TEMPERATURE;
/** Refraction correction from local pressure and temperature. */
private double correfrac = 1.;
/** Threshold apparent elevation value. */
private final double elevation;
/** Topocentric frame in which elevation should be evaluated. */
private final TopocentricFrame topo;
/** Build a new apparent elevation detector.
* <p>This simple constructor takes default values for maximal checking
* interval ({@link #DEFAULT_MAXCHECK}) and convergence threshold
* ({@link #DEFAULT_THRESHOLD}).</p>
* @param elevation threshold elevation value
* @param topo topocentric frame in which elevation should be evaluated
*/
public ApparentElevationDetector(final double elevation, final TopocentricFrame topo) {
this(DEFAULT_MAXCHECK, DEFAULT_THRESHOLD, elevation, topo);
}
/** Build a new apparent elevation detector.
* <p>This constructor takes default value for convergence threshold
* ({@link #DEFAULT_THRESHOLD}).</p>
* <p>The maximal interval between elevation checks should
* be smaller than the half duration of the minimal pass to handle,
* otherwise some short passes could be missed.</p>
* @param maxCheck maximal checking interval (s)
* @param elevation threshold elevation value (rad)
* @param topo topocentric frame in which elevation should be evaluated
*/
public ApparentElevationDetector(final double maxCheck,
final double elevation,
final TopocentricFrame topo) {
this(maxCheck, DEFAULT_THRESHOLD, elevation, topo);
}
/** Build a new apparent elevation detector.
* <p>The maximal interval between elevation checks should
* be smaller than the half duration of the minimal pass to handle,
* otherwise some short passes could be missed.</p>
* @param maxCheck maximal checking interval (s)
* @param threshold convergence threshold (s)
* @param elevation threshold elevation value (rad)
* @param topo topocentric frame in which elevation should be evaluated
*/
public ApparentElevationDetector(final double maxCheck,
final double threshold,
final double elevation,
final TopocentricFrame topo) {
this(maxCheck, threshold, DEFAULT_MAX_ITER, new StopOnDecreasing<ApparentElevationDetector>(),
elevation, 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 maxIter maximum number of iterations in the event time search
* @param threshold convergence threshold (s)
* @param handler event handler to call at event occurrences
* @param elevation threshold elevation value (rad)
* @param topo topocentric frame in which elevation should be evaluated
* @since 6.1
*/
private ApparentElevationDetector(final double maxCheck, final double threshold,
final int maxIter, final EventHandler<ApparentElevationDetector> handler,
final double elevation,
final TopocentricFrame topo) {
super(maxCheck, threshold, maxIter, handler);
this.elevation = elevation;
this.topo = topo;
}
/** {@inheritDoc} */
@Override
protected ApparentElevationDetector create(final double newMaxCheck, final double newThreshold,
final int newMaxIter, final EventHandler<ApparentElevationDetector> newHandler) {
return new ApparentElevationDetector(newMaxCheck, newThreshold, newMaxIter, newHandler,
elevation, topo);
}
/** Set the local pressure at topocentric frame origin if needed.
* <p>Otherwise the default value for the local pressure is set to {@link #DEFAULT_PRESSURE}.</p>
* @param pressure the pressure to set (Pa)
*/
public void setPressure(final double pressure) {
this.pressure = pressure;
this.correfrac = (pressure / DEFAULT_PRESSURE) * (DEFAULT_TEMPERATURE / temperature);
}
/** Set the local temperature at topocentric frame origin if needed.
* <p>Otherwise the default value for the local temperature is set to {@link #DEFAULT_TEMPERATURE}.</p>
* @param temperature the temperature to set (K)
*/
public void setTemperature(final double temperature) {
this.temperature = temperature;
this.correfrac = (pressure / DEFAULT_PRESSURE) * (DEFAULT_TEMPERATURE / temperature);
}
/** Get the threshold apparent elevation value.
* @return the threshold apparent elevation value (rad)
*/
public double getElevation() {
return elevation;
}
/** Get the topocentric frame.
* @return the topocentric frame
*/
public TopocentricFrame getTopocentricFrame() {
return topo;
}
/** Get the local pressure at topocentric frame origin.
* @return the pressure
*/
public double getPressure() {
return pressure;
}
/** Get the local temperature at topocentric frame origin.
* @return the temperature
*/
public double getTemperature() {
return temperature;
}
/** Compute the value of the switching function.
* <p>This function measures the difference between the current apparent elevation
* and the threshold apparent elevation.</p>
* @param s the current state information: date, kinematics, attitude
* @return value of the switching function
* @exception OrekitException if some specific error occurs
*/
public double g(final SpacecraftState s) throws OrekitException {
final double trueElevation = topo.getElevation(s.getPVCoordinates().getPosition(), s.getFrame(), s.getDate());
return trueElevation + getRefraction(trueElevation) - elevation;
}
/** Compute the refraction angle from the true (geometrical) elevation.
* @param trueElevation true elevation (rad)
* @return refraction angle (rad)
*/
private double getRefraction(final double trueElevation) {
double refraction = 0.0;
final double eld = FastMath.toDegrees(trueElevation);
if (eld > MIN_ELEVATION && eld < MAX_ELEVATION) {
final double tmp = eld + 10.3 / (eld + 5.11);
final double ref = 1.02 / FastMath.tan(FastMath.toRadians(tmp)) / 60.;
refraction = FastMath.toRadians(correfrac * ref);
}
return refraction;
}
}