PVCoordinates.java
/* Copyright 2002-2016 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.utils;
import java.io.Serializable;
import org.hipparchus.analysis.differentiation.DerivativeStructure;
import org.hipparchus.geometry.euclidean.threed.FieldVector3D;
import org.hipparchus.geometry.euclidean.threed.Vector3D;
import org.orekit.errors.OrekitException;
import org.orekit.errors.OrekitMessages;
import org.orekit.time.TimeShiftable;
/** Simple container for Position/Velocity/Acceleration triplets.
* <p>
* The state can be slightly shifted to close dates. This shift is based on
* a simple quadratic model. 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>
* <p>
* This class is the angular counterpart to {@link AngularCoordinates}.
* </p>
* <p>Instances of this class are guaranteed to be immutable.</p>
* @author Fabien Maussion
* @author Luc Maisonobe
*/
public class PVCoordinates implements TimeShiftable<PVCoordinates>, Serializable {
/** Fixed position/velocity at origin (both p, v and a are zero vectors). */
public static final PVCoordinates ZERO = new PVCoordinates(Vector3D.ZERO, Vector3D.ZERO, Vector3D.ZERO);
/** Serializable UID. */
private static final long serialVersionUID = 20140407L;
/** The position. */
private final Vector3D position;
/** The velocity. */
private final Vector3D velocity;
/** The acceleration. */
private final Vector3D acceleration;
/** Simple constructor.
* <p> Set the Coordinates to default : (0 0 0), (0 0 0), (0 0 0).</p>
*/
public PVCoordinates() {
position = Vector3D.ZERO;
velocity = Vector3D.ZERO;
acceleration = Vector3D.ZERO;
}
/** Builds a PVCoordinates triplet with zero acceleration.
* <p>Acceleration is set to zero</p>
* @param position the position vector (m)
* @param velocity the velocity vector (m/s)
*/
public PVCoordinates(final Vector3D position, final Vector3D velocity) {
this.position = position;
this.velocity = velocity;
this.acceleration = Vector3D.ZERO;
}
/** Builds a PVCoordinates triplet.
* @param position the position vector (m)
* @param velocity the velocity vector (m/s)
* @param acceleration the acceleration vector (m/s²)
*/
public PVCoordinates(final Vector3D position, final Vector3D velocity, final Vector3D acceleration) {
this.position = position;
this.velocity = velocity;
this.acceleration = acceleration;
}
/** Multiplicative constructor.
* <p>Build a PVCoordinates from another one and a scale factor.</p>
* <p>The PVCoordinates built will be a * pv</p>
* @param a scale factor
* @param pv base (unscaled) PVCoordinates
*/
public PVCoordinates(final double a, final PVCoordinates pv) {
position = new Vector3D(a, pv.position);
velocity = new Vector3D(a, pv.velocity);
acceleration = new Vector3D(a, pv.acceleration);
}
/** Subtractive constructor.
* <p>Build a relative PVCoordinates from a start and an end position.</p>
* <p>The PVCoordinates built will be end - start.</p>
* @param start Starting PVCoordinates
* @param end ending PVCoordinates
*/
public PVCoordinates(final PVCoordinates start, final PVCoordinates end) {
this.position = end.position.subtract(start.position);
this.velocity = end.velocity.subtract(start.velocity);
this.acceleration = end.acceleration.subtract(start.acceleration);
}
/** Linear constructor.
* <p>Build a PVCoordinates from two other ones and corresponding scale factors.</p>
* <p>The PVCoordinates built will be a1 * u1 + a2 * u2</p>
* @param a1 first scale factor
* @param pv1 first base (unscaled) PVCoordinates
* @param a2 second scale factor
* @param pv2 second base (unscaled) PVCoordinates
*/
public PVCoordinates(final double a1, final PVCoordinates pv1,
final double a2, final PVCoordinates pv2) {
position = new Vector3D(a1, pv1.position, a2, pv2.position);
velocity = new Vector3D(a1, pv1.velocity, a2, pv2.velocity);
acceleration = new Vector3D(a1, pv1.acceleration, a2, pv2.acceleration);
}
/** Linear constructor.
* <p>Build a PVCoordinates from three other ones and corresponding scale factors.</p>
* <p>The PVCoordinates built will be a1 * u1 + a2 * u2 + a3 * u3</p>
* @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 PVCoordinates(final double a1, final PVCoordinates pv1,
final double a2, final PVCoordinates pv2,
final double a3, final PVCoordinates pv3) {
position = new Vector3D(a1, pv1.position, a2, pv2.position, a3, pv3.position);
velocity = new Vector3D(a1, pv1.velocity, a2, pv2.velocity, a3, pv3.velocity);
acceleration = new Vector3D(a1, pv1.acceleration, a2, pv2.acceleration, a3, pv3.acceleration);
}
/** Linear constructor.
* <p>Build a PVCoordinates from four other ones and corresponding scale factors.</p>
* <p>The PVCoordinates built will be a1 * u1 + a2 * u2 + a3 * u3 + a4 * u4</p>
* @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 PVCoordinates(final double a1, final PVCoordinates pv1,
final double a2, final PVCoordinates pv2,
final double a3, final PVCoordinates pv3,
final double a4, final PVCoordinates pv4) {
position = new Vector3D(a1, pv1.position, a2, pv2.position,
a3, pv3.position, a4, pv4.position);
velocity = new Vector3D(a1, pv1.velocity, a2, pv2.velocity,
a3, pv3.velocity, a4, pv4.velocity);
acceleration = new Vector3D(a1, pv1.acceleration, a2, pv2.acceleration,
a3, pv3.acceleration, a4, pv4.acceleration);
}
/** Builds a PVCoordinates 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 p vector with time-derivatives embedded within the coordinates
*/
public PVCoordinates(final FieldVector3D<DerivativeStructure> p) {
position = new Vector3D(p.getX().getReal(), p.getY().getReal(), p.getZ().getReal());
if (p.getX().getOrder() >= 1) {
velocity = new Vector3D(p.getX().getPartialDerivative(1),
p.getY().getPartialDerivative(1),
p.getZ().getPartialDerivative(1));
if (p.getX().getOrder() >= 2) {
acceleration = new Vector3D(p.getX().getPartialDerivative(2),
p.getY().getPartialDerivative(2),
p.getZ().getPartialDerivative(2));
} else {
acceleration = Vector3D.ZERO;
}
} else {
velocity = Vector3D.ZERO;
acceleration = Vector3D.ZERO;
}
}
/** Transform the instance to a {@link FieldVector3D}<{@link DerivativeStructure}>.
* <p>
* The {@link DerivativeStructure} coordinates correspond to time-derivatives up
* to the user-specified order.
* </p>
* @param order derivation order for the vector components (must be either 0, 1 or 2)
* @return vector with time-derivatives embedded within the coordinates
* @exception OrekitException if the user specified order is too large
*/
public FieldVector3D<DerivativeStructure> toDerivativeStructureVector(final int order)
throws OrekitException {
final DerivativeStructure x;
final DerivativeStructure y;
final DerivativeStructure z;
switch(order) {
case 0 :
x = new DerivativeStructure(1, 0, position.getX());
y = new DerivativeStructure(1, 0, position.getY());
z = new DerivativeStructure(1, 0, position.getZ());
break;
case 1 :
x = new DerivativeStructure(1, 1, position.getX(), velocity.getX());
y = new DerivativeStructure(1, 1, position.getY(), velocity.getY());
z = new DerivativeStructure(1, 1, position.getZ(), velocity.getZ());
break;
case 2 :
x = new DerivativeStructure(1, 2, position.getX(), velocity.getX(), acceleration.getX());
y = new DerivativeStructure(1, 2, position.getY(), velocity.getY(), acceleration.getY());
z = new DerivativeStructure(1, 2, position.getZ(), velocity.getZ(), acceleration.getZ());
break;
default :
throw new OrekitException(OrekitMessages.OUT_OF_RANGE_DERIVATION_ORDER, order);
}
return new FieldVector3D<DerivativeStructure>(x, y, z);
}
/** Estimate velocity between two positions.
* <p>Estimation is based on a simple fixed velocity translation
* during the time interval between the two positions.</p>
* @param start start position
* @param end end position
* @param dt time elapsed between the dates of the two positions
* @return velocity allowing to go from start to end positions
*/
public static Vector3D estimateVelocity(final Vector3D start, final Vector3D end, final double dt) {
final double scale = 1.0 / dt;
return new Vector3D(scale, end, -scale, start);
}
/** 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 PVCoordinates shiftedBy(final double dt) {
return new PVCoordinates(new Vector3D(1, position, dt, velocity, 0.5 * dt * dt, acceleration),
new Vector3D(1, velocity, dt, acceleration),
acceleration);
}
/** Gets the position.
* @return the position vector (m).
*/
public Vector3D getPosition() {
return position;
}
/** Gets the velocity.
* @return the velocity vector (m/s).
*/
public Vector3D getVelocity() {
return velocity;
}
/** Gets the acceleration.
* @return the acceleration vector (m/s²).
*/
public Vector3D getAcceleration() {
return acceleration;
}
/** Gets the momentum.
* <p>This vector is the p ⊗ v where p is position, v is velocity
* and ⊗ is cross product. To get the real physical angular momentum
* you need to multiply this vector by the mass.</p>
* <p>The returned vector is recomputed each time this method is called, it
* is not cached.</p>
* @return a new instance of the momentum vector (m²/s).
*/
public Vector3D getMomentum() {
return Vector3D.crossProduct(position, velocity);
}
/**
* Get the angular velocity (spin) of this point as seen from the origin.
*
* <p> The angular velocity vector is parallel to the {@link #getMomentum()
* angular momentum} and is computed by ω = p × v / ||p||²
*
* @return the angular velocity vector
* @see <a href="http://en.wikipedia.org/wiki/Angular_velocity">Angular Velocity on
* Wikipedia</a>
*/
public Vector3D getAngularVelocity() {
return this.getMomentum().scalarMultiply(1.0 / this.getPosition().getNormSq());
}
/** Get the opposite of the instance.
* @return a new position-velocity which is opposite to the instance
*/
public PVCoordinates negate() {
return new PVCoordinates(position.negate(), velocity.negate(), acceleration.negate());
}
/** Normalize the position part of the instance.
* <p>
* The computed coordinates first component (position) will be a
* normalized vector, the second component (velocity) will be the
* derivative of the first component (hence it will generally not
* be normalized), and the third component (acceleration) will be the
* derivative of the second component (hence it will generally not
* be normalized).
* </p>
* @return a new instance, with first component normalized and
* remaining component computed to have consistent derivatives
*/
public PVCoordinates normalize() {
final double inv = 1.0 / position.getNorm();
final Vector3D u = new Vector3D(inv, position);
final Vector3D v = new Vector3D(inv, velocity);
final Vector3D w = new Vector3D(inv, acceleration);
final double uv = Vector3D.dotProduct(u, v);
final double v2 = Vector3D.dotProduct(v, v);
final double uw = Vector3D.dotProduct(u, w);
final Vector3D uDot = new Vector3D(1, v, -uv, u);
final Vector3D uDotDot = new Vector3D(1, w, -2 * uv, v, 3 * uv * uv - v2 - uw, u);
return new PVCoordinates(u, uDot, uDotDot);
}
/** Compute the cross-product of two instances.
* @param pv1 first instances
* @param pv2 second instances
* @return the cross product v1 ^ v2 as a new instance
*/
public static PVCoordinates crossProduct(final PVCoordinates pv1, final PVCoordinates pv2) {
final Vector3D p1 = pv1.position;
final Vector3D v1 = pv1.velocity;
final Vector3D a1 = pv1.acceleration;
final Vector3D p2 = pv2.position;
final Vector3D v2 = pv2.velocity;
final Vector3D a2 = pv2.acceleration;
return new PVCoordinates(Vector3D.crossProduct(p1, p2),
new Vector3D(1, Vector3D.crossProduct(p1, v2),
1, Vector3D.crossProduct(v1, p2)),
new Vector3D(1, Vector3D.crossProduct(p1, a2),
2, Vector3D.crossProduct(v1, v2),
1, Vector3D.crossProduct(a1, p2)));
}
/** Return a string representation of this position/velocity pair.
* @return string representation of this position/velocity pair
*/
public String toString() {
final String comma = ", ";
return new StringBuffer().append('{').append("P(").
append(position.getX()).append(comma).
append(position.getY()).append(comma).
append(position.getZ()).append("), V(").
append(velocity.getX()).append(comma).
append(velocity.getY()).append(comma).
append(velocity.getZ()).append("), A(").
append(acceleration.getX()).append(comma).
append(acceleration.getY()).append(comma).
append(acceleration.getZ()).append(")}").toString();
}
/** Replace the instance with a data transfer object for serialization.
* @return data transfer object that will be serialized
*/
private Object writeReplace() {
return new DTO(this);
}
/** Internal class used only for serialization. */
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 PVCoordinates pv) {
this.d = new double[] {
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 PVCoordinates}.
* @return replacement {@link PVCoordinates}
*/
private Object readResolve() {
return new PVCoordinates(new Vector3D(d[0], d[1], d[2]),
new Vector3D(d[3], d[4], d[5]),
new Vector3D(d[6], d[7], d[8]));
}
}
}