SpacecraftState.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;
import java.io.Serializable;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import org.apache.commons.math3.analysis.interpolation.HermiteInterpolator;
import org.apache.commons.math3.exception.DimensionMismatchException;
import org.orekit.attitudes.Attitude;
import org.orekit.attitudes.LofOffset;
import org.orekit.errors.OrekitException;
import org.orekit.errors.OrekitMessages;
import org.orekit.frames.Frame;
import org.orekit.frames.LOFType;
import org.orekit.frames.Transform;
import org.orekit.orbits.Orbit;
import org.orekit.time.AbsoluteDate;
import org.orekit.time.TimeInterpolable;
import org.orekit.time.TimeShiftable;
import org.orekit.time.TimeStamped;
import org.orekit.utils.PVCoordinates;
/** This class is the representation of a complete state holding orbit, attitude
* and mass information at a given date.
*
* <p>It contains an {@link Orbit orbital state} at a current
* {@link AbsoluteDate} both handled by an {@link Orbit}, plus the current
* mass and attitude. Orbit and state are guaranteed to be consistent in terms
* of date and reference frame. The spacecraft state may also contain additional
* states, which are simply named double arrays which can hold any user-defined
* data.
* </p>
* <p>
* The state can be slightly shifted to close dates. This shift is based on
* a simple keplerian model for orbit, a linear extrapolation for attitude
* taking the spin rate into account and no mass change. It is <em>not</em>
* intended as a replacement for proper orbit and attitude propagation but
* should be sufficient for either small time shifts or coarse accuracy.
* </p>
* <p>
* The instance <code>SpacecraftState</code> is guaranteed to be immutable.
* </p>
* @see org.orekit.propagation.numerical.NumericalPropagator
* @author Fabien Maussion
* @author Véronique Pommier-Maurussane
* @author Luc Maisonobe
*/
public class SpacecraftState
implements TimeStamped, TimeShiftable<SpacecraftState>, TimeInterpolable<SpacecraftState>, Serializable {
/** Serializable UID. */
private static final long serialVersionUID = 20130407L;
/** Default mass. */
private static final double DEFAULT_MASS = 1000.0;
/** Orbital state. */
private final Orbit orbit;
/** Attitude. */
private final Attitude attitude;
/** Current mass (kg). */
private final double mass;
/** Additional states. */
private final Map<String, double[]> additional;
/** Build a spacecraft state from orbit only.
* <p>Attitude and mass are set to unspecified non-null arbitrary values.</p>
* @param orbit the orbit
* @exception OrekitException if default attitude cannot be computed
*/
public SpacecraftState(final Orbit orbit)
throws OrekitException {
this(orbit,
new LofOffset(orbit.getFrame(), LOFType.VVLH).getAttitude(orbit, orbit.getDate(), orbit.getFrame()),
DEFAULT_MASS, null);
}
/** Build a spacecraft state from orbit and attitude provider.
* <p>Mass is set to an unspecified non-null arbitrary value.</p>
* @param orbit the orbit
* @param attitude attitude
* @exception IllegalArgumentException if orbit and attitude dates
* or frames are not equal
*/
public SpacecraftState(final Orbit orbit, final Attitude attitude)
throws IllegalArgumentException {
this(orbit, attitude, DEFAULT_MASS, null);
}
/** Create a new instance from orbit and mass.
* <p>Attitude law is set to an unspecified default attitude.</p>
* @param orbit the orbit
* @param mass the mass (kg)
* @exception OrekitException if default attitude cannot be computed
*/
public SpacecraftState(final Orbit orbit, final double mass)
throws OrekitException {
this(orbit,
new LofOffset(orbit.getFrame(), LOFType.VVLH).getAttitude(orbit, orbit.getDate(), orbit.getFrame()),
mass, null);
}
/** Build a spacecraft state from orbit, attitude provider and mass.
* @param orbit the orbit
* @param attitude attitude
* @param mass the mass (kg)
* @exception IllegalArgumentException if orbit and attitude dates
* or frames are not equal
*/
public SpacecraftState(final Orbit orbit, final Attitude attitude, final double mass)
throws IllegalArgumentException {
this(orbit, attitude, mass, null);
}
/** Build a spacecraft state from orbit only.
* <p>Attitude and mass are set to unspecified non-null arbitrary values.</p>
* @param orbit the orbit
* @param additional additional states
* @exception OrekitException if default attitude cannot be computed
*/
public SpacecraftState(final Orbit orbit, final Map<String, double[]> additional)
throws OrekitException {
this(orbit,
new LofOffset(orbit.getFrame(), LOFType.VVLH).getAttitude(orbit, orbit.getDate(), orbit.getFrame()),
DEFAULT_MASS, additional);
}
/** Build a spacecraft state from orbit and attitude provider.
* <p>Mass is set to an unspecified non-null arbitrary value.</p>
* @param orbit the orbit
* @param attitude attitude
* @param additional additional states
* @exception IllegalArgumentException if orbit and attitude dates
* or frames are not equal
*/
public SpacecraftState(final Orbit orbit, final Attitude attitude, final Map<String, double[]> additional)
throws IllegalArgumentException {
this(orbit, attitude, DEFAULT_MASS, additional);
}
/** Create a new instance from orbit and mass.
* <p>Attitude law is set to an unspecified default attitude.</p>
* @param orbit the orbit
* @param mass the mass (kg)
* @param additional additional states
* @exception OrekitException if default attitude cannot be computed
*/
public SpacecraftState(final Orbit orbit, final double mass, final Map<String, double[]> additional)
throws OrekitException {
this(orbit,
new LofOffset(orbit.getFrame(), LOFType.VVLH).getAttitude(orbit, orbit.getDate(), orbit.getFrame()),
mass, additional);
}
/** Build a spacecraft state from orbit, attitude provider and mass.
* @param orbit the orbit
* @param attitude attitude
* @param mass the mass (kg)
* @param additional additional states (may be null if no additional states are available)
* @exception IllegalArgumentException if orbit and attitude dates
* or frames are not equal
*/
public SpacecraftState(final Orbit orbit, final Attitude attitude,
final double mass, final Map<String, double[]> additional)
throws IllegalArgumentException {
checkConsistency(orbit, attitude);
this.orbit = orbit;
this.attitude = attitude;
this.mass = mass;
if (additional == null) {
this.additional = Collections.emptyMap();
} else {
this.additional = new HashMap<String, double[]>(additional.size());
for (final Map.Entry<String, double[]> entry : additional.entrySet()) {
this.additional.put(entry.getKey(), entry.getValue().clone());
}
}
}
/** Add an additional state.
* <p>
* {@link SpacecraftState SpacecraftState} instances are immutable,
* so this method does <em>not</em> change the instance, but rather
* creates a new instance, which has the same orbit, attitude, mass
* and additional states as the original instance, except it also
* has the specified state. If the original instance already had an
* additional state with the same name, it will be overridden. If it
* did not have any additional state with that name, the new instance
* will have one more additional state than the original instance.
* </p>
* @param name name of the additional state
* @param value value of the additional state
* @return a new instance, with the additional state added
* @see #hasAdditionalState(String)
* @see #getAdditionalState(String)
* @see #getAdditionalStates()
*/
public SpacecraftState addAdditionalState(final String name, final double ... value) {
final Map<String, double[]> newMap = new HashMap<String, double[]>(additional.size() + 1);
newMap.putAll(additional);
newMap.put(name, value.clone());
return new SpacecraftState(orbit, attitude, mass, newMap);
}
/** Check orbit and attitude dates are equal.
* @param orbit the orbit
* @param attitude attitude
* @exception IllegalArgumentException if orbit and attitude dates
* are not equal
*/
private static void checkConsistency(final Orbit orbit, final Attitude attitude)
throws IllegalArgumentException {
if (!orbit.getDate().equals(attitude.getDate())) {
throw OrekitException.createIllegalArgumentException(
OrekitMessages.ORBIT_AND_ATTITUDE_DATES_MISMATCH,
orbit.getDate(), attitude.getDate());
}
if (orbit.getFrame() != attitude.getReferenceFrame()) {
throw OrekitException.createIllegalArgumentException(
OrekitMessages.FRAMES_MISMATCH,
orbit.getFrame().getName(), attitude.getReferenceFrame().getName());
}
}
/** Get a time-shifted state.
* <p>
* The state can be slightly shifted to close dates. This shift is based on
* a simple keplerian model for orbit, a linear extrapolation for attitude
* taking the spin rate into account and neither mass nor additional states
* changes. It is <em>not</em> intended as a replacement for proper orbit
* and attitude propagation but should be sufficient for small time shifts
* or coarse accuracy.
* </p>
* <p>
* As a rough order of magnitude, the following table shows the interpolation
* errors obtained between this simple shift method and an {@link
* org.orekit.propagation.analytical.EcksteinHechlerPropagator Eckstein-Heschler
* propagator} for an 800km altitude nearly circular polar Earth orbit with
* {@link org.orekit.attitudes.BodyCenterPointing body center pointing}. Beware
* that these results may be different for other orbits.
* </p>
* <table border="1" cellpadding="5">
* <tr bgcolor="#ccccff"><th>interpolation time (s)</th>
* <th>position error (m)</th><th>velocity error (m/s)</th>
* <th>attitude error (°)</th></tr>
* <tr><td bgcolor="#eeeeff"> 60</td><td> 20</td><td>1</td><td>0.001</td></tr>
* <tr><td bgcolor="#eeeeff">120</td><td> 100</td><td>2</td><td>0.002</td></tr>
* <tr><td bgcolor="#eeeeff">300</td><td> 600</td><td>4</td><td>0.005</td></tr>
* <tr><td bgcolor="#eeeeff">600</td><td>2000</td><td>6</td><td>0.008</td></tr>
* <tr><td bgcolor="#eeeeff">900</td><td>4000</td><td>6</td><td>0.010</td></tr>
* </table>
* @param dt time shift in seconds
* @return a new state, shifted with respect to the instance (which is immutable)
* except for the mass which stay unchanged
*/
public SpacecraftState shiftedBy(final double dt) {
return new SpacecraftState(orbit.shiftedBy(dt), attitude.shiftedBy(dt),
mass, additional);
}
/** {@inheritDoc}
* <p>
* The additional states that are interpolated are the ones already present
* in the instance. The sample instances must therefore have at least the same
* additional states has the instance. They may have more additional states,
* but the extra ones will be ignored.
* </p>
* <p>
* As this implementation of interpolation is polynomial, it should be used only
* with small samples (about 10-20 points) in order to avoid <a
* href="http://en.wikipedia.org/wiki/Runge%27s_phenomenon">Runge's phenomenon</a>
* and numerical problems (including NaN appearing).
* </p>
*/
public SpacecraftState interpolate(final AbsoluteDate date,
final Collection<SpacecraftState> sample)
throws OrekitException {
// prepare interpolators
final List<Orbit> orbits = new ArrayList<Orbit>(sample.size());
final List<Attitude> attitudes = new ArrayList<Attitude>(sample.size());
final HermiteInterpolator massInterpolator = new HermiteInterpolator();
final Map<String, HermiteInterpolator> additionalInterpolators =
new HashMap<String, HermiteInterpolator>(additional.size());
for (final String name : additional.keySet()) {
additionalInterpolators.put(name, new HermiteInterpolator());
}
// extract sample data
for (final SpacecraftState state : sample) {
final double deltaT = state.getDate().durationFrom(date);
orbits.add(state.getOrbit());
attitudes.add(state.getAttitude());
massInterpolator.addSamplePoint(deltaT,
new double[] {
state.getMass()
});
for (final Map.Entry<String, HermiteInterpolator> entry : additionalInterpolators.entrySet()) {
entry.getValue().addSamplePoint(deltaT, state.getAdditionalState(entry.getKey()));
}
}
// perform interpolations
final Orbit interpolatedOrbit = orbit.interpolate(date, orbits);
final Attitude interpolatedAttitude = attitude.interpolate(date, attitudes);
final double interpolatedMass = massInterpolator.value(0)[0];
final Map<String, double[]> interpolatedAdditional;
if (additional.isEmpty()) {
interpolatedAdditional = null;
} else {
interpolatedAdditional = new HashMap<String, double[]>(additional.size());
for (final Map.Entry<String, HermiteInterpolator> entry : additionalInterpolators.entrySet()) {
interpolatedAdditional.put(entry.getKey(), entry.getValue().value(0));
}
}
// create the complete interpolated state
return new SpacecraftState(interpolatedOrbit, interpolatedAttitude,
interpolatedMass, interpolatedAdditional);
}
/** Gets the current orbit.
* @return the orbit
*/
public Orbit getOrbit() {
return orbit;
}
/** Get the date.
* @return date
*/
public AbsoluteDate getDate() {
return orbit.getDate();
}
/** Get the inertial frame.
* @return the frame
*/
public Frame getFrame() {
return orbit.getFrame();
}
/** Check if an additional state is available.
* @param name name of the additional state
* @return true if the additional state is available
* @see #addAdditionalState(String, double[])
* @see #getAdditionalState(String)
* @see #getAdditionalStates()
*/
public boolean hasAdditionalState(final String name) {
return additional.containsKey(name);
}
/** Check if two instances have the same set of additional states available.
* <p>
* Only the names and dimensions of the additional states are compared,
* not their values.
* </p>
* @param state state to compare to instance
* @exception OrekitException if either instance or state supports an additional
* state not supported by the other one
* @exception DimensionMismatchException if an additional state does not have
* the same dimension in both states
*/
public void ensureCompatibleAdditionalStates(final SpacecraftState state)
throws OrekitException, DimensionMismatchException {
// check instance additional states is a subset of the other one
for (final Map.Entry<String, double[]> entry : additional.entrySet()) {
final double[] other = state.additional.get(entry.getKey());
if (other == null) {
throw new OrekitException(OrekitMessages.UNKNOWN_ADDITIONAL_STATE,
entry.getKey());
}
if (other.length != entry.getValue().length) {
throw new DimensionMismatchException(other.length, entry.getValue().length);
}
}
if (state.additional.size() > additional.size()) {
// the other state has more additional states
for (final String name : state.additional.keySet()) {
if (!additional.containsKey(name)) {
throw new OrekitException(OrekitMessages.UNKNOWN_ADDITIONAL_STATE,
name);
}
}
}
}
/** Get an additional state.
* @param name name of the additional state
* @return value of the additional state
* @exception OrekitException if no additional state with that name exists
* @see #addAdditionalState(String, double[])
* @see #hasAdditionalState(String)
* @see #getAdditionalStates()
*/
public double[] getAdditionalState(final String name) throws OrekitException {
if (!additional.containsKey(name)) {
throw new OrekitException(OrekitMessages.UNKNOWN_ADDITIONAL_STATE, name);
}
return additional.get(name).clone();
}
/** Get an unmodifiable map of additional states.
* @return unmodifiable map of additional states
* @see #addAdditionalState(String, double[])
* @see #hasAdditionalState(String)
* @see #getAdditionalState(String)
*/
public Map<String, double[]> getAdditionalStates() {
return Collections.unmodifiableMap(additional);
}
/** Compute the transform from orbite/attitude reference frame to spacecraft frame.
* <p>The spacecraft frame origin is at the point defined by the orbit,
* and its orientation is defined by the attitude.</p>
* @return transform from specified frame to current spacecraft frame
*/
public Transform toTransform() {
final AbsoluteDate date = orbit.getDate();
return new Transform(date,
new Transform(date, orbit.getPVCoordinates().negate()),
new Transform(date, attitude.getOrientation()));
}
/** Get the central attraction coefficient.
* @return mu central attraction coefficient (m^3/s^2)
*/
public double getMu() {
return orbit.getMu();
}
/** Get the keplerian period.
* <p>The keplerian period is computed directly from semi major axis
* and central acceleration constant.</p>
* @return keplerian period in seconds
*/
public double getKeplerianPeriod() {
return orbit.getKeplerianPeriod();
}
/** Get the keplerian mean motion.
* <p>The keplerian mean motion is computed directly from semi major axis
* and central acceleration constant.</p>
* @return keplerian mean motion in radians per second
*/
public double getKeplerianMeanMotion() {
return orbit.getKeplerianMeanMotion();
}
/** Get the semi-major axis.
* @return semi-major axis (m)
*/
public double getA() {
return orbit.getA();
}
/** Get the first component of the eccentricity vector (as per equinoctial parameters).
* @return e cos(ω + Ω), first component of eccentricity vector
* @see #getE()
*/
public double getEquinoctialEx() {
return orbit.getEquinoctialEx();
}
/** Get the second component of the eccentricity vector (as per equinoctial parameters).
* @return e sin(ω + Ω), second component of the eccentricity vector
* @see #getE()
*/
public double getEquinoctialEy() {
return orbit.getEquinoctialEy();
}
/** Get the first component of the inclination vector (as per equinoctial parameters).
* @return tan(i/2) cos(Ω), first component of the inclination vector
* @see #getI()
*/
public double getHx() {
return orbit.getHx();
}
/** Get the second component of the inclination vector (as per equinoctial parameters).
* @return tan(i/2) sin(Ω), second component of the inclination vector
* @see #getI()
*/
public double getHy() {
return orbit.getHy();
}
/** Get the true latitude argument (as per equinoctial parameters).
* @return v + ω + Ω true latitude argument (rad)
* @see #getLE()
* @see #getLM()
*/
public double getLv() {
return orbit.getLv();
}
/** Get the eccentric latitude argument (as per equinoctial parameters).
* @return E + ω + Ω eccentric latitude argument (rad)
* @see #getLv()
* @see #getLM()
*/
public double getLE() {
return orbit.getLE();
}
/** Get the mean latitude argument (as per equinoctial parameters).
* @return M + ω + Ω mean latitude argument (rad)
* @see #getLv()
* @see #getLE()
*/
public double getLM() {
return orbit.getLM();
}
// Additional orbital elements
/** Get the eccentricity.
* @return eccentricity
* @see #getEquinoctialEx()
* @see #getEquinoctialEy()
*/
public double getE() {
return orbit.getE();
}
/** Get the inclination.
* @return inclination (rad)
* @see #getHx()
* @see #getHy()
*/
public double getI() {
return orbit.getI();
}
/** Get the {@link PVCoordinates} in orbit definition frame.
* Compute the position and velocity of the satellite. This method caches its
* results, and recompute them only when the method is called with a new value
* for mu. The result is provided as a reference to the internally cached
* {@link PVCoordinates}, so the caller is responsible to copy it in a separate
* {@link PVCoordinates} if it needs to keep the value for a while.
* @return pvCoordinates in orbit definition frame
*/
public PVCoordinates getPVCoordinates() {
return orbit.getPVCoordinates();
}
/** Get the {@link PVCoordinates} in given output frame.
* Compute the position and velocity of the satellite. This method caches its
* results, and recompute them only when the method is called with a new value
* for mu. The result is provided as a reference to the internally cached
* {@link PVCoordinates}, so the caller is responsible to copy it in a separate
* {@link PVCoordinates} if it needs to keep the value for a while.
* @param outputFrame frame in which coordinates should be defined
* @return pvCoordinates in orbit definition frame
* @exception OrekitException if the transformation between frames cannot be computed
*/
public PVCoordinates getPVCoordinates(final Frame outputFrame)
throws OrekitException {
return orbit.getPVCoordinates(outputFrame);
}
/** Get the attitude.
* @return the attitude.
*/
public Attitude getAttitude() {
return attitude;
}
/** Gets the current mass.
* @return the mass (kg)
*/
public double getMass() {
return mass;
}
}