TimeStampedPVCoordinates.java
/* Copyright 2002-2020 CS Group
* 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.
* 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.utils;
import java.io.Serializable;
import java.util.Collection;
import java.util.stream.Stream;
import org.hipparchus.analysis.differentiation.DerivativeStructure;
import org.hipparchus.analysis.interpolation.HermiteInterpolator;
import org.hipparchus.geometry.euclidean.threed.FieldVector3D;
import org.hipparchus.geometry.euclidean.threed.Vector3D;
import org.hipparchus.util.FastMath;
import org.orekit.annotation.DefaultDataContext;
import org.orekit.data.DataContext;
import org.orekit.errors.OrekitInternalError;
import org.orekit.frames.Frame;
import org.orekit.frames.Transform;
import org.orekit.time.AbsoluteDate;
import org.orekit.time.TimeScale;
import org.orekit.time.TimeStamped;
/** {@link TimeStamped time-stamped} version of {@link PVCoordinates}.
* <p>Instances of this class are guaranteed to be immutable.</p>
* @author Luc Maisonobe
* @since 7.0
*/
public class TimeStampedPVCoordinates extends PVCoordinates implements TimeStamped {
/** Serializable UID. */
private static final long serialVersionUID = 20140723L;
/** The date. */
private final AbsoluteDate date;
/** Builds a TimeStampedPVCoordinates pair.
* @param date coordinates date
* @param position the position vector (m)
* @param velocity the velocity vector (m/s)
* @param acceleration the acceleration vector (m/s²)
*/
public TimeStampedPVCoordinates(final AbsoluteDate date,
final Vector3D position, final Vector3D velocity, final Vector3D acceleration) {
super(position, velocity, acceleration);
this.date = date;
}
/**
* Build from position and velocity. Acceleration is set to zero.
*
* @param date coordinates date
* @param position the position vector (m)
* @param velocity the velocity vector (m/s)
*/
public TimeStampedPVCoordinates(final AbsoluteDate date,
final Vector3D position,
final Vector3D velocity) {
this(date, position, velocity, Vector3D.ZERO);
}
/**
* Build from position velocity acceleration coordinates.
*
* @param date coordinates date
* @param pv position velocity, and acceleration coordinates, in meters and seconds.
*/
public TimeStampedPVCoordinates(final AbsoluteDate date, final PVCoordinates pv) {
this(date, pv.getPosition(), pv.getVelocity(), pv.getAcceleration());
}
/** Multiplicative constructor
* <p>Build a TimeStampedPVCoordinates from another one and a scale factor.</p>
* <p>The TimeStampedPVCoordinates built will be a * pv</p>
* @param date date of the built coordinates
* @param a scale factor
* @param pv base (unscaled) PVCoordinates
*/
public TimeStampedPVCoordinates(final AbsoluteDate date,
final double a, final PVCoordinates pv) {
super(new Vector3D(a, pv.getPosition()),
new Vector3D(a, pv.getVelocity()),
new Vector3D(a, pv.getAcceleration()));
this.date = date;
}
/** Subtractive constructor
* <p>Build a relative TimeStampedPVCoordinates from a start and an end position.</p>
* <p>The TimeStampedPVCoordinates built will be end - start.</p>
* @param date date of the built coordinates
* @param start Starting PVCoordinates
* @param end ending PVCoordinates
*/
public TimeStampedPVCoordinates(final AbsoluteDate date,
final PVCoordinates start, final PVCoordinates end) {
super(end.getPosition().subtract(start.getPosition()),
end.getVelocity().subtract(start.getVelocity()),
end.getAcceleration().subtract(start.getAcceleration()));
this.date = date;
}
/** Linear constructor
* <p>Build a TimeStampedPVCoordinates from two other ones and corresponding scale factors.</p>
* <p>The TimeStampedPVCoordinates built will be a1 * u1 + a2 * u2</p>
* @param date date of the built coordinates
* @param a1 first scale factor
* @param pv1 first base (unscaled) PVCoordinates
* @param a2 second scale factor
* @param pv2 second base (unscaled) PVCoordinates
*/
public TimeStampedPVCoordinates(final AbsoluteDate date,
final double a1, final PVCoordinates pv1,
final double a2, final PVCoordinates pv2) {
super(new Vector3D(a1, pv1.getPosition(), a2, pv2.getPosition()),
new Vector3D(a1, pv1.getVelocity(), a2, pv2.getVelocity()),
new Vector3D(a1, pv1.getAcceleration(), a2, pv2.getAcceleration()));
this.date = date;
}
/** Linear constructor
* <p>Build a TimeStampedPVCoordinates from three other ones and corresponding scale factors.</p>
* <p>The TimeStampedPVCoordinates built will be a1 * u1 + a2 * u2 + a3 * u3</p>
* @param date date of the built coordinates
* @param a1 first scale factor
* @param pv1 first base (unscaled) PVCoordinates
* @param a2 second scale factor
* @param pv2 second base (unscaled) PVCoordinates
* @param a3 third scale factor
* @param pv3 third base (unscaled) PVCoordinates
*/
public TimeStampedPVCoordinates(final AbsoluteDate date,
final double a1, final PVCoordinates pv1,
final double a2, final PVCoordinates pv2,
final double a3, final PVCoordinates pv3) {
super(new Vector3D(a1, pv1.getPosition(), a2, pv2.getPosition(), a3, pv3.getPosition()),
new Vector3D(a1, pv1.getVelocity(), a2, pv2.getVelocity(), a3, pv3.getVelocity()),
new Vector3D(a1, pv1.getAcceleration(), a2, pv2.getAcceleration(), a3, pv3.getAcceleration()));
this.date = date;
}
/** Linear constructor
* <p>Build a TimeStampedPVCoordinates from four other ones and corresponding scale factors.</p>
* <p>The TimeStampedPVCoordinates built will be a1 * u1 + a2 * u2 + a3 * u3 + a4 * u4</p>
* @param date date of the built coordinates
* @param a1 first scale factor
* @param pv1 first base (unscaled) PVCoordinates
* @param a2 second scale factor
* @param pv2 second base (unscaled) PVCoordinates
* @param a3 third scale factor
* @param pv3 third base (unscaled) PVCoordinates
* @param a4 fourth scale factor
* @param pv4 fourth base (unscaled) PVCoordinates
*/
public TimeStampedPVCoordinates(final AbsoluteDate date,
final double a1, final PVCoordinates pv1,
final double a2, final PVCoordinates pv2,
final double a3, final PVCoordinates pv3,
final double a4, final PVCoordinates pv4) {
super(new Vector3D(a1, pv1.getPosition(), a2, pv2.getPosition(), a3, pv3.getPosition(), a4, pv4.getPosition()),
new Vector3D(a1, pv1.getVelocity(), a2, pv2.getVelocity(), a3, pv3.getVelocity(), a4, pv4.getVelocity()),
new Vector3D(a1, pv1.getAcceleration(), a2, pv2.getAcceleration(), a3, pv3.getAcceleration(), a4, pv4.getAcceleration()));
this.date = date;
}
/** Builds a TimeStampedPVCoordinates triplet from a {@link FieldVector3D}<{@link DerivativeStructure}>.
* <p>
* The vector components must have time as their only derivation parameter and
* have consistent derivation orders.
* </p>
* @param date date of the built coordinates
* @param p vector with time-derivatives embedded within the coordinates
*/
public TimeStampedPVCoordinates(final AbsoluteDate date,
final FieldVector3D<DerivativeStructure> p) {
super(p);
this.date = date;
}
/** {@inheritDoc} */
public AbsoluteDate getDate() {
return date;
}
/** Get a time-shifted state.
* <p>
* The state can be slightly shifted to close dates. This shift is based on
* a simple Taylor expansion. It is <em>not</em> intended as a replacement for
* proper orbit propagation (it is not even Keplerian!) but should be sufficient
* for either small time shifts or coarse accuracy.
* </p>
* @param dt time shift in seconds
* @return a new state, shifted with respect to the instance (which is immutable)
*/
public TimeStampedPVCoordinates shiftedBy(final double dt) {
final PVCoordinates spv = super.shiftedBy(dt);
return new TimeStampedPVCoordinates(date.shiftedBy(dt),
spv.getPosition(), spv.getVelocity(), spv.getAcceleration());
}
/** Create a local provider using simply Taylor expansion through {@link #shiftedBy(double)}.
* <p>
* The time evolution is based on a simple Taylor expansion. It is <em>not</em> intended as a
* replacement for proper orbit propagation (it is not even Keplerian!) but should be sufficient
* for either small time shifts or coarse accuracy.
* </p>
* @param instanceFrame frame in which the instance is defined
* @return provider based on Taylor expansion, for small time shifts around instance date
*/
public PVCoordinatesProvider toTaylorProvider(final Frame instanceFrame) {
return new PVCoordinatesProvider() {
/** {@inheritDoc} */
public TimeStampedPVCoordinates getPVCoordinates(final AbsoluteDate d, final Frame f) {
final TimeStampedPVCoordinates shifted = shiftedBy(d.durationFrom(date));
final Transform transform = instanceFrame.getTransformTo(f, d);
return transform.transformPVCoordinates(shifted);
}
};
}
/** Interpolate position-velocity.
* <p>
* The interpolated instance is created by polynomial Hermite interpolation
* ensuring velocity remains the exact derivative of position.
* </p>
* <p>
* Note that even if first time derivatives (velocities)
* from sample can be ignored, the interpolated instance always includes
* interpolated derivatives. This feature can be used explicitly to
* compute these derivatives when it would be too complex to compute them
* from an analytical formula: just compute a few sample points from the
* explicit formula and set the derivatives to zero in these sample points,
* then use interpolation to add derivatives consistent with the positions.
* </p>
* @param date interpolation date
* @param filter filter for derivatives from the sample to use in interpolation
* @param sample sample points on which interpolation should be done
* @return a new position-velocity, interpolated at specified date
*/
public static TimeStampedPVCoordinates interpolate(final AbsoluteDate date,
final CartesianDerivativesFilter filter,
final Collection<TimeStampedPVCoordinates> sample) {
return interpolate(date, filter, sample.stream());
}
/** Interpolate position-velocity.
* <p>
* The interpolated instance is created by polynomial Hermite interpolation
* ensuring velocity remains the exact derivative of position.
* </p>
* <p>
* Note that even if first time derivatives (velocities)
* from sample can be ignored, the interpolated instance always includes
* interpolated derivatives. This feature can be used explicitly to
* compute these derivatives when it would be too complex to compute them
* from an analytical formula: just compute a few sample points from the
* explicit formula and set the derivatives to zero in these sample points,
* then use interpolation to add derivatives consistent with the positions.
* </p>
* @param date interpolation date
* @param filter filter for derivatives from the sample to use in interpolation
* @param sample sample points on which interpolation should be done
* @return a new position-velocity, interpolated at specified date
* @since 9.0
*/
public static TimeStampedPVCoordinates interpolate(final AbsoluteDate date,
final CartesianDerivativesFilter filter,
final Stream<TimeStampedPVCoordinates> sample) {
// set up an interpolator taking derivatives into account
final HermiteInterpolator interpolator = new HermiteInterpolator();
// add sample points
switch (filter) {
case USE_P :
// populate sample with position data, ignoring velocity
sample.forEach(pv -> {
final Vector3D position = pv.getPosition();
interpolator.addSamplePoint(pv.getDate().durationFrom(date),
position.toArray());
});
break;
case USE_PV :
// populate sample with position and velocity data
sample.forEach(pv -> {
final Vector3D position = pv.getPosition();
final Vector3D velocity = pv.getVelocity();
interpolator.addSamplePoint(pv.getDate().durationFrom(date),
position.toArray(), velocity.toArray());
});
break;
case USE_PVA :
// populate sample with position, velocity and acceleration data
sample.forEach(pv -> {
final Vector3D position = pv.getPosition();
final Vector3D velocity = pv.getVelocity();
final Vector3D acceleration = pv.getAcceleration();
interpolator.addSamplePoint(pv.getDate().durationFrom(date),
position.toArray(), velocity.toArray(), acceleration.toArray());
});
break;
default :
// this should never happen
throw new OrekitInternalError(null);
}
// interpolate
final double[][] p = interpolator.derivatives(0.0, 2);
// build a new interpolated instance
return new TimeStampedPVCoordinates(date, new Vector3D(p[0]), new Vector3D(p[1]), new Vector3D(p[2]));
}
/** Return a string representation of this date, position, velocity, and acceleration.
*
* <p>This method uses the {@link DataContext#getDefault() default data context}.
*
* @return string representation of this.
*/
@Override
@DefaultDataContext
public String toString() {
return toString(DataContext.getDefault().getTimeScales().getUTC());
}
/**
* Return a string representation of this date, position, velocity, and acceleration.
*
* @param utc time scale used to print the date.
* @return string representation of this.
*/
public String toString(final TimeScale utc) {
final String comma = ", ";
return new StringBuffer().append('{').
append(date.toString(utc)).append(", P(").
append(getPosition().getX()).append(comma).
append(getPosition().getY()).append(comma).
append(getPosition().getZ()).append("), V(").
append(getVelocity().getX()).append(comma).
append(getVelocity().getY()).append(comma).
append(getVelocity().getZ()).append("), A(").
append(getAcceleration().getX()).append(comma).
append(getAcceleration().getY()).append(comma).
append(getAcceleration().getZ()).append(")}").toString();
}
/** Replace the instance with a data transfer object for serialization.
* @return data transfer object that will be serialized
*/
@DefaultDataContext
private Object writeReplace() {
return new DTO(this);
}
/** Internal class used only for serialization. */
@DefaultDataContext
private static class DTO implements Serializable {
/** Serializable UID. */
private static final long serialVersionUID = 20140723L;
/** Double values. */
private double[] d;
/** Simple constructor.
* @param pv instance to serialize
*/
private DTO(final TimeStampedPVCoordinates pv) {
// decompose date
final AbsoluteDate j2000Epoch =
DataContext.getDefault().getTimeScales().getJ2000Epoch();
final double epoch = FastMath.floor(pv.getDate().durationFrom(j2000Epoch));
final double offset = pv.getDate().durationFrom(j2000Epoch.shiftedBy(epoch));
this.d = new double[] {
epoch, offset,
pv.getPosition().getX(), pv.getPosition().getY(), pv.getPosition().getZ(),
pv.getVelocity().getX(), pv.getVelocity().getY(), pv.getVelocity().getZ(),
pv.getAcceleration().getX(), pv.getAcceleration().getY(), pv.getAcceleration().getZ()
};
}
/** Replace the deserialized data transfer object with a {@link TimeStampedPVCoordinates}.
* @return replacement {@link TimeStampedPVCoordinates}
*/
private Object readResolve() {
final AbsoluteDate j2000Epoch =
DataContext.getDefault().getTimeScales().getJ2000Epoch();
return new TimeStampedPVCoordinates(j2000Epoch.shiftedBy(d[0]).shiftedBy(d[1]),
new Vector3D(d[2], d[3], d[ 4]),
new Vector3D(d[5], d[6], d[ 7]),
new Vector3D(d[8], d[9], d[10]));
}
}
}