Transform.java
/* Copyright 2002-2024 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
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*
* http://www.apache.org/licenses/LICENSE-2.0
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* Unless required by applicable law or agreed to in writing, software
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package org.orekit.frames;
import java.io.Serializable;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.List;
import java.util.stream.Collectors;
import java.util.stream.Stream;
import org.hipparchus.CalculusFieldElement;
import org.hipparchus.geometry.euclidean.threed.Line;
import org.hipparchus.geometry.euclidean.threed.Rotation;
import org.hipparchus.geometry.euclidean.threed.Vector3D;
import org.orekit.time.AbsoluteDate;
import org.orekit.time.TimeInterpolator;
import org.orekit.time.TimeShiftable;
import org.orekit.utils.AngularCoordinates;
import org.orekit.utils.AngularDerivativesFilter;
import org.orekit.utils.CartesianDerivativesFilter;
import org.orekit.utils.FieldPVCoordinates;
import org.orekit.utils.PVCoordinates;
import org.orekit.utils.TimeStampedAngularCoordinates;
import org.orekit.utils.TimeStampedAngularCoordinatesHermiteInterpolator;
import org.orekit.utils.TimeStampedFieldPVCoordinates;
import org.orekit.utils.TimeStampedPVCoordinates;
import org.orekit.utils.TimeStampedPVCoordinatesHermiteInterpolator;
/** Transformation class in three dimensional space.
*
* <p>This class represents the transformation engine between {@link Frame frames}.
* It is used both to define the relationship between each frame and its
* parent frame and to gather all individual transforms into one
* operation when converting between frames far away from each other.</p>
* <p> The convention used in OREKIT is vectorial transformation. It means
* that a transformation is defined as a transform to apply to the
* coordinates of a vector expressed in the old frame to obtain the
* same vector expressed in the new frame.
*
* <p>Instances of this class are guaranteed to be immutable.</p>
*
* <h2> Examples </h2>
*
* <h3> Example of translation from R<sub>A</sub> to R<sub>B</sub> </h3>
*
* <p> We want to transform the {@link PVCoordinates} PV<sub>A</sub> to
* PV<sub>B</sub> with :
* <p> PV<sub>A</sub> = ({1, 0, 0}, {2, 0, 0}, {3, 0, 0}); <br>
* PV<sub>B</sub> = ({0, 0, 0}, {0, 0, 0}, {0, 0, 0});
*
* <p> The transform to apply then is defined as follows :
*
* <pre><code>
* Vector3D translation = new Vector3D(-1, 0, 0);
* Vector3D velocity = new Vector3D(-2, 0, 0);
* Vector3D acceleration = new Vector3D(-3, 0, 0);
*
* Transform R1toR2 = new Transform(date, translation, velocity, acceleration);
*
* PVB = R1toR2.transformPVCoordinates(PVA);
* </code></pre>
*
* <h3> Example of rotation from R<sub>A</sub> to R<sub>B</sub> </h3>
* <p> We want to transform the {@link PVCoordinates} PV<sub>A</sub> to
* PV<sub>B</sub> with
*
* <p> PV<sub>A</sub> = ({1, 0, 0}, { 1, 0, 0}); <br>
* PV<sub>B</sub> = ({0, 1, 0}, {-2, 1, 0});
*
* <p> The transform to apply then is defined as follows :
*
* <pre><code>
* Rotation rotation = new Rotation(Vector3D.PLUS_K, FastMath.PI / 2);
* Vector3D rotationRate = new Vector3D(0, 0, -2);
*
* Transform R1toR2 = new Transform(rotation, rotationRate);
*
* PVB = R1toR2.transformPVCoordinates(PVA);
* </code></pre>
*
* @author Luc Maisonobe
* @author Fabien Maussion
*/
public class Transform implements
TimeShiftable<Transform>,
Serializable,
KinematicTransform {
/** Identity transform. */
public static final Transform IDENTITY = new IdentityTransform();
/** Serializable UID. */
private static final long serialVersionUID = 210140410L;
/** Date of the transform. */
private final AbsoluteDate date;
/** Cartesian coordinates of the target frame with respect to the original frame. */
private final PVCoordinates cartesian;
/** Angular coordinates of the target frame with respect to the original frame. */
private final AngularCoordinates angular;
/** Build a transform from its primitive operations.
* @param date date of the transform
* @param cartesian Cartesian coordinates of the target frame with respect to the original frame
* @param angular angular coordinates of the target frame with respect to the original frame
*/
public Transform(final AbsoluteDate date, final PVCoordinates cartesian, final AngularCoordinates angular) {
this.date = date;
this.cartesian = cartesian;
this.angular = angular;
}
/** Build a translation transform.
* @param date date of the transform
* @param translation translation to apply (i.e. coordinates of
* the transformed origin, or coordinates of the origin of the
* old frame in the new frame)
*/
public Transform(final AbsoluteDate date, final Vector3D translation) {
this(date,
new PVCoordinates(translation),
AngularCoordinates.IDENTITY);
}
/** Build a rotation transform.
* @param date date of the transform
* @param rotation rotation to apply ( i.e. rotation to apply to the
* coordinates of a vector expressed in the old frame to obtain the
* same vector expressed in the new frame )
*/
public Transform(final AbsoluteDate date, final Rotation rotation) {
this(date,
PVCoordinates.ZERO,
new AngularCoordinates(rotation));
}
/** Build a combined translation and rotation transform.
* @param date date of the transform
* @param translation translation to apply (i.e. coordinates of
* the transformed origin, or coordinates of the origin of the
* old frame in the new frame)
* @param rotation rotation to apply ( i.e. rotation to apply to the
* coordinates of a vector expressed in the old frame to obtain the
* same vector expressed in the new frame )
* @since 12.1
*/
public Transform(final AbsoluteDate date, final Vector3D translation, final Rotation rotation) {
this(date, new PVCoordinates(translation), new AngularCoordinates(rotation));
}
/** Build a translation transform, with its first time derivative.
* @param date date of the transform
* @param translation translation to apply (i.e. coordinates of
* the transformed origin, or coordinates of the origin of the
* old frame in the new frame)
* @param velocity the velocity of the translation (i.e. origin
* of the old frame velocity in the new frame)
*/
public Transform(final AbsoluteDate date, final Vector3D translation,
final Vector3D velocity) {
this(date,
new PVCoordinates(translation, velocity, Vector3D.ZERO),
AngularCoordinates.IDENTITY);
}
/** Build a translation transform, with its first and second time derivatives.
* @param date date of the transform
* @param translation translation to apply (i.e. coordinates of
* the transformed origin, or coordinates of the origin of the
* old frame in the new frame)
* @param velocity the velocity of the translation (i.e. origin
* of the old frame velocity in the new frame)
* @param acceleration the acceleration of the translation (i.e. origin
* of the old frame acceleration in the new frame)
*/
public Transform(final AbsoluteDate date, final Vector3D translation,
final Vector3D velocity, final Vector3D acceleration) {
this(date,
new PVCoordinates(translation, velocity, acceleration),
AngularCoordinates.IDENTITY);
}
/** Build a translation transform, with its first time derivative.
* @param date date of the transform
* @param cartesian Cartesian part of the transformation to apply (i.e. coordinates of
* the transformed origin, or coordinates of the origin of the
* old frame in the new frame, with their derivatives)
*/
public Transform(final AbsoluteDate date, final PVCoordinates cartesian) {
this(date,
cartesian,
AngularCoordinates.IDENTITY);
}
/** Build a rotation transform.
* @param date date of the transform
* @param rotation rotation to apply ( i.e. rotation to apply to the
* coordinates of a vector expressed in the old frame to obtain the
* same vector expressed in the new frame )
* @param rotationRate the axis of the instant rotation
* expressed in the new frame. (norm representing angular rate)
*/
public Transform(final AbsoluteDate date, final Rotation rotation, final Vector3D rotationRate) {
this(date,
PVCoordinates.ZERO,
new AngularCoordinates(rotation, rotationRate, Vector3D.ZERO));
}
/** Build a rotation transform.
* @param date date of the transform
* @param rotation rotation to apply ( i.e. rotation to apply to the
* coordinates of a vector expressed in the old frame to obtain the
* same vector expressed in the new frame )
* @param rotationRate the axis of the instant rotation
* @param rotationAcceleration the axis of the instant rotation
* expressed in the new frame. (norm representing angular rate)
*/
public Transform(final AbsoluteDate date, final Rotation rotation, final Vector3D rotationRate,
final Vector3D rotationAcceleration) {
this(date,
PVCoordinates.ZERO,
new AngularCoordinates(rotation, rotationRate, rotationAcceleration));
}
/** Build a rotation transform.
* @param date date of the transform
* @param angular angular part of the transformation to apply (i.e. rotation to
* apply to the coordinates of a vector expressed in the old frame to obtain the
* same vector expressed in the new frame, with its rotation rate)
*/
public Transform(final AbsoluteDate date, final AngularCoordinates angular) {
this(date, PVCoordinates.ZERO, angular);
}
/** Build a transform by combining two existing ones.
* <p>
* Note that the dates of the two existing transformed are <em>ignored</em>,
* and the combined transform date is set to the date supplied in this constructor
* without any attempt to shift the raw transforms. This is a design choice allowing
* user full control of the combination.
* </p>
* @param date date of the transform
* @param first first transform applied
* @param second second transform applied
*/
public Transform(final AbsoluteDate date, final Transform first, final Transform second) {
this(date,
new PVCoordinates(StaticTransform.compositeTranslation(first, second),
KinematicTransform.compositeVelocity(first, second),
compositeAcceleration(first, second)),
new AngularCoordinates(StaticTransform.compositeRotation(first, second),
KinematicTransform.compositeRotationRate(first, second),
compositeRotationAcceleration(first, second)));
}
/** Compute a composite acceleration.
* @param first first applied transform
* @param second second applied transform
* @return acceleration part of the composite transform
*/
private static Vector3D compositeAcceleration(final Transform first, final Transform second) {
final Vector3D a1 = first.cartesian.getAcceleration();
final Rotation r1 = first.angular.getRotation();
final Vector3D o1 = first.angular.getRotationRate();
final Vector3D oDot1 = first.angular.getRotationAcceleration();
final Vector3D p2 = second.cartesian.getPosition();
final Vector3D v2 = second.cartesian.getVelocity();
final Vector3D a2 = second.cartesian.getAcceleration();
final Vector3D crossCrossP = Vector3D.crossProduct(o1, Vector3D.crossProduct(o1, p2));
final Vector3D crossV = Vector3D.crossProduct(o1, v2);
final Vector3D crossDotP = Vector3D.crossProduct(oDot1, p2);
return a1.add(r1.applyInverseTo(new Vector3D(1, a2, 2, crossV, 1, crossCrossP, 1, crossDotP)));
}
/** Compute a composite rotation acceleration.
* @param first first applied transform
* @param second second applied transform
* @return rotation acceleration part of the composite transform
*/
private static Vector3D compositeRotationAcceleration(final Transform first, final Transform second) {
final Vector3D o1 = first.angular.getRotationRate();
final Vector3D oDot1 = first.angular.getRotationAcceleration();
final Rotation r2 = second.angular.getRotation();
final Vector3D o2 = second.angular.getRotationRate();
final Vector3D oDot2 = second.angular.getRotationAcceleration();
return new Vector3D( 1, oDot2,
1, r2.applyTo(oDot1),
-1, Vector3D.crossProduct(o2, r2.applyTo(o1)));
}
/** {@inheritDoc} */
public AbsoluteDate getDate() {
return date;
}
/** {@inheritDoc} */
public Transform shiftedBy(final double dt) {
return new Transform(date.shiftedBy(dt), cartesian.shiftedBy(dt), angular.shiftedBy(dt));
}
/**
* Shift the transform in time considering all rates, then return only the
* translation and rotation portion of the transform.
*
* @param dt time shift in seconds.
* @return shifted transform as a static transform. It is static in the
* sense that it can only be used to transform directions and positions, but
* not velocities or accelerations.
* @see #shiftedBy(double)
*/
public StaticTransform staticShiftedBy(final double dt) {
return StaticTransform.of(
date.shiftedBy(dt),
cartesian.positionShiftedBy(dt),
angular.rotationShiftedBy(dt));
}
/**
* Create a so-called static transform from the instance.
*
* @return static part of the transform. It is static in the
* sense that it can only be used to transform directions and positions, but
* not velocities or accelerations.
* @see StaticTransform
*/
public StaticTransform toStaticTransform() {
return StaticTransform.of(date, cartesian.getPosition(), angular.getRotation());
}
/** Interpolate a transform from a sample set of existing transforms.
* <p>
* Calling this method is equivalent to call {@link #interpolate(AbsoluteDate,
* CartesianDerivativesFilter, AngularDerivativesFilter, Collection)} with {@code cFilter}
* set to {@link CartesianDerivativesFilter#USE_PVA} and {@code aFilter} set to
* {@link AngularDerivativesFilter#USE_RRA}
* set to true.
* </p>
* @param interpolationDate interpolation date
* @param sample sample points on which interpolation should be done
* @return a new instance, interpolated at specified date
*/
public Transform interpolate(final AbsoluteDate interpolationDate, final Stream<Transform> sample) {
return interpolate(interpolationDate,
CartesianDerivativesFilter.USE_PVA, AngularDerivativesFilter.USE_RRA,
sample.collect(Collectors.toList()));
}
/** Interpolate a transform from a sample set of existing transforms.
* <p>
* Note that even if first time derivatives (velocities and rotation rates)
* 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
* and rotations.
* </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>
* @param date interpolation date
* @param cFilter filter for derivatives from the sample to use in interpolation
* @param aFilter filter for derivatives from the sample to use in interpolation
* @param sample sample points on which interpolation should be done
* @return a new instance, interpolated at specified date
* @since 7.0
*/
public static Transform interpolate(final AbsoluteDate date,
final CartesianDerivativesFilter cFilter,
final AngularDerivativesFilter aFilter,
final Collection<Transform> sample) {
// Create samples
final List<TimeStampedPVCoordinates> datedPV = new ArrayList<>(sample.size());
final List<TimeStampedAngularCoordinates> datedAC = new ArrayList<>(sample.size());
for (final Transform t : sample) {
datedPV.add(new TimeStampedPVCoordinates(t.getDate(), t.getTranslation(), t.getVelocity(), t.getAcceleration()));
datedAC.add(new TimeStampedAngularCoordinates(t.getDate(), t.getRotation(), t.getRotationRate(), t.getRotationAcceleration()));
}
// Create interpolators
final TimeInterpolator<TimeStampedPVCoordinates> pvInterpolator =
new TimeStampedPVCoordinatesHermiteInterpolator(datedPV.size(), cFilter);
final TimeInterpolator<TimeStampedAngularCoordinates> angularInterpolator =
new TimeStampedAngularCoordinatesHermiteInterpolator(datedPV.size(), aFilter);
// Interpolate
final TimeStampedPVCoordinates interpolatedPV = pvInterpolator.interpolate(date, datedPV);
final TimeStampedAngularCoordinates interpolatedAC = angularInterpolator.interpolate(date, datedAC);
return new Transform(date, interpolatedPV, interpolatedAC);
}
/** Get the inverse transform of the instance.
* @return inverse transform of the instance
*/
@Override
public Transform getInverse() {
final Rotation r = angular.getRotation();
final Vector3D o = angular.getRotationRate();
final Vector3D oDot = angular.getRotationAcceleration();
final Vector3D rp = r.applyTo(cartesian.getPosition());
final Vector3D rv = r.applyTo(cartesian.getVelocity());
final Vector3D ra = r.applyTo(cartesian.getAcceleration());
final Vector3D pInv = rp.negate();
final Vector3D crossP = Vector3D.crossProduct(o, rp);
final Vector3D vInv = crossP.subtract(rv);
final Vector3D crossV = Vector3D.crossProduct(o, rv);
final Vector3D crossDotP = Vector3D.crossProduct(oDot, rp);
final Vector3D crossCrossP = Vector3D.crossProduct(o, crossP);
final Vector3D aInv = new Vector3D(-1, ra,
2, crossV,
1, crossDotP,
-1, crossCrossP);
return new Transform(getDate(), new PVCoordinates(pInv, vInv, aInv), angular.revert());
}
/** Get a frozen transform.
* <p>
* This method creates a copy of the instance but frozen in time,
* i.e. with velocity, acceleration and rotation rate forced to zero.
* </p>
* @return a new transform, without any time-dependent parts
*/
public Transform freeze() {
return new Transform(date,
new PVCoordinates(cartesian.getPosition(), Vector3D.ZERO, Vector3D.ZERO),
new AngularCoordinates(angular.getRotation(), Vector3D.ZERO, Vector3D.ZERO));
}
/** Transform {@link PVCoordinates} including kinematic effects.
* @param pva the position-velocity-acceleration triplet to transform.
* @return transformed position-velocity-acceleration
*/
public PVCoordinates transformPVCoordinates(final PVCoordinates pva) {
return angular.applyTo(new PVCoordinates(1, pva, 1, cartesian));
}
/** Transform {@link TimeStampedPVCoordinates} including kinematic effects.
* <p>
* In order to allow the user more flexibility, this method does <em>not</em> check for
* consistency between the transform {@link #getDate() date} and the time-stamped
* position-velocity {@link TimeStampedPVCoordinates#getDate() date}. The returned
* value will always have the same {@link TimeStampedPVCoordinates#getDate() date} as
* the input argument, regardless of the instance {@link #getDate() date}.
* </p>
* @param pv time-stamped position-velocity to transform.
* @return transformed time-stamped position-velocity
* @since 7.0
*/
public TimeStampedPVCoordinates transformPVCoordinates(final TimeStampedPVCoordinates pv) {
return angular.applyTo(new TimeStampedPVCoordinates(pv.getDate(), 1, pv, 1, cartesian));
}
/** Transform {@link FieldPVCoordinates} including kinematic effects.
* @param pv position-velocity to transform.
* @param <T> type of the field elements
* @return transformed position-velocity
*/
public <T extends CalculusFieldElement<T>> FieldPVCoordinates<T> transformPVCoordinates(final FieldPVCoordinates<T> pv) {
return angular.applyTo(new FieldPVCoordinates<>(pv.getPosition().add(cartesian.getPosition()),
pv.getVelocity().add(cartesian.getVelocity()),
pv.getAcceleration().add(cartesian.getAcceleration())));
}
/** Transform {@link TimeStampedFieldPVCoordinates} including kinematic effects.
* <p>
* In order to allow the user more flexibility, this method does <em>not</em> check for
* consistency between the transform {@link #getDate() date} and the time-stamped
* position-velocity {@link TimeStampedFieldPVCoordinates#getDate() date}. The returned
* value will always have the same {@link TimeStampedFieldPVCoordinates#getDate() date} as
* the input argument, regardless of the instance {@link #getDate() date}.
* </p>
* @param pv time-stamped position-velocity to transform.
* @param <T> type of the field elements
* @return transformed time-stamped position-velocity
* @since 7.0
*/
public <T extends CalculusFieldElement<T>> TimeStampedFieldPVCoordinates<T> transformPVCoordinates(final TimeStampedFieldPVCoordinates<T> pv) {
return angular.applyTo(new TimeStampedFieldPVCoordinates<>(pv.getDate(),
pv.getPosition().add(cartesian.getPosition()),
pv.getVelocity().add(cartesian.getVelocity()),
pv.getAcceleration().add(cartesian.getAcceleration())));
}
/** Compute the Jacobian of the {@link #transformPVCoordinates(PVCoordinates)}
* method of the transform.
* <p>
* Element {@code jacobian[i][j]} is the derivative of Cartesian coordinate i
* of the transformed {@link PVCoordinates} with respect to Cartesian coordinate j
* of the input {@link PVCoordinates} in method {@link #transformPVCoordinates(PVCoordinates)}.
* </p>
* <p>
* This definition implies that if we define position-velocity coordinates
* <pre>
* PV₁ = transform.transformPVCoordinates(PV₀), then
* </pre>
* <p> their differentials dPV₁ and dPV₀ will obey the following relation
* where J is the matrix computed by this method:
* <pre>
* dPV₁ = J × dPV₀
* </pre>
*
* @param selector selector specifying the size of the upper left corner that must be filled
* (either 3x3 for positions only, 6x6 for positions and velocities, 9x9 for positions,
* velocities and accelerations)
* @param jacobian placeholder matrix whose upper-left corner is to be filled with
* the Jacobian, the rest of the matrix remaining untouched
*/
public void getJacobian(final CartesianDerivativesFilter selector, final double[][] jacobian) {
// elementary matrix for rotation
final double[][] mData = angular.getRotation().getMatrix();
// dP1/dP0
System.arraycopy(mData[0], 0, jacobian[0], 0, 3);
System.arraycopy(mData[1], 0, jacobian[1], 0, 3);
System.arraycopy(mData[2], 0, jacobian[2], 0, 3);
if (selector.getMaxOrder() >= 1) {
// dP1/dV0
Arrays.fill(jacobian[0], 3, 6, 0.0);
Arrays.fill(jacobian[1], 3, 6, 0.0);
Arrays.fill(jacobian[2], 3, 6, 0.0);
// dV1/dP0
final Vector3D o = angular.getRotationRate();
final double ox = o.getX();
final double oy = o.getY();
final double oz = o.getZ();
for (int i = 0; i < 3; ++i) {
jacobian[3][i] = -(oy * mData[2][i] - oz * mData[1][i]);
jacobian[4][i] = -(oz * mData[0][i] - ox * mData[2][i]);
jacobian[5][i] = -(ox * mData[1][i] - oy * mData[0][i]);
}
// dV1/dV0
System.arraycopy(mData[0], 0, jacobian[3], 3, 3);
System.arraycopy(mData[1], 0, jacobian[4], 3, 3);
System.arraycopy(mData[2], 0, jacobian[5], 3, 3);
if (selector.getMaxOrder() >= 2) {
// dP1/dA0
Arrays.fill(jacobian[0], 6, 9, 0.0);
Arrays.fill(jacobian[1], 6, 9, 0.0);
Arrays.fill(jacobian[2], 6, 9, 0.0);
// dV1/dA0
Arrays.fill(jacobian[3], 6, 9, 0.0);
Arrays.fill(jacobian[4], 6, 9, 0.0);
Arrays.fill(jacobian[5], 6, 9, 0.0);
// dA1/dP0
final Vector3D oDot = angular.getRotationAcceleration();
final double oDotx = oDot.getX();
final double oDoty = oDot.getY();
final double oDotz = oDot.getZ();
for (int i = 0; i < 3; ++i) {
jacobian[6][i] = -(oDoty * mData[2][i] - oDotz * mData[1][i]) - (oy * jacobian[5][i] - oz * jacobian[4][i]);
jacobian[7][i] = -(oDotz * mData[0][i] - oDotx * mData[2][i]) - (oz * jacobian[3][i] - ox * jacobian[5][i]);
jacobian[8][i] = -(oDotx * mData[1][i] - oDoty * mData[0][i]) - (ox * jacobian[4][i] - oy * jacobian[3][i]);
}
// dA1/dV0
for (int i = 0; i < 3; ++i) {
jacobian[6][i + 3] = -2 * (oy * mData[2][i] - oz * mData[1][i]);
jacobian[7][i + 3] = -2 * (oz * mData[0][i] - ox * mData[2][i]);
jacobian[8][i + 3] = -2 * (ox * mData[1][i] - oy * mData[0][i]);
}
// dA1/dA0
System.arraycopy(mData[0], 0, jacobian[6], 6, 3);
System.arraycopy(mData[1], 0, jacobian[7], 6, 3);
System.arraycopy(mData[2], 0, jacobian[8], 6, 3);
}
}
}
/** Get the underlying elementary Cartesian part.
* <p>A transform can be uniquely represented as an elementary
* translation followed by an elementary rotation. This method
* returns this unique elementary translation with its derivative.</p>
* @return underlying elementary Cartesian part
* @see #getTranslation()
* @see #getVelocity()
*/
public PVCoordinates getCartesian() {
return cartesian;
}
/** Get the underlying elementary translation.
* <p>A transform can be uniquely represented as an elementary
* translation followed by an elementary rotation. This method
* returns this unique elementary translation.</p>
* @return underlying elementary translation
* @see #getCartesian()
* @see #getVelocity()
* @see #getAcceleration()
*/
public Vector3D getTranslation() {
return cartesian.getPosition();
}
/** Get the first time derivative of the translation.
* @return first time derivative of the translation
* @see #getCartesian()
* @see #getTranslation()
* @see #getAcceleration()
*/
public Vector3D getVelocity() {
return cartesian.getVelocity();
}
/** Get the second time derivative of the translation.
* @return second time derivative of the translation
* @see #getCartesian()
* @see #getTranslation()
* @see #getVelocity()
*/
public Vector3D getAcceleration() {
return cartesian.getAcceleration();
}
/** Get the underlying elementary angular part.
* <p>A transform can be uniquely represented as an elementary
* translation followed by an elementary rotation. This method
* returns this unique elementary rotation with its derivative.</p>
* @return underlying elementary angular part
* @see #getRotation()
* @see #getRotationRate()
* @see #getRotationAcceleration()
*/
public AngularCoordinates getAngular() {
return angular;
}
/** Get the underlying elementary rotation.
* <p>A transform can be uniquely represented as an elementary
* translation followed by an elementary rotation. This method
* returns this unique elementary rotation.</p>
* @return underlying elementary rotation
* @see #getAngular()
* @see #getRotationRate()
* @see #getRotationAcceleration()
*/
public Rotation getRotation() {
return angular.getRotation();
}
/** Get the first time derivative of the rotation.
* <p>The norm represents the angular rate.</p>
* @return First time derivative of the rotation
* @see #getAngular()
* @see #getRotation()
* @see #getRotationAcceleration()
*/
public Vector3D getRotationRate() {
return angular.getRotationRate();
}
/** Get the second time derivative of the rotation.
* @return Second time derivative of the rotation
* @see #getAngular()
* @see #getRotation()
* @see #getRotationRate()
*/
public Vector3D getRotationAcceleration() {
return angular.getRotationAcceleration();
}
/** Specialized class for identity transform. */
private static class IdentityTransform extends Transform {
/** Serializable UID. */
private static final long serialVersionUID = -9042082036141830517L;
/** Simple constructor. */
IdentityTransform() {
super(AbsoluteDate.ARBITRARY_EPOCH, PVCoordinates.ZERO, AngularCoordinates.IDENTITY);
}
/** {@inheritDoc} */
@Override
public Transform shiftedBy(final double dt) {
return this;
}
/** {@inheritDoc} */
@Override
public Transform getInverse() {
return this;
}
/** {@inheritDoc} */
@Override
public Vector3D transformPosition(final Vector3D position) {
return position;
}
/** {@inheritDoc} */
@Override
public Vector3D transformVector(final Vector3D vector) {
return vector;
}
/** {@inheritDoc} */
@Override
public Line transformLine(final Line line) {
return line;
}
/** {@inheritDoc} */
@Override
public PVCoordinates transformPVCoordinates(final PVCoordinates pv) {
return pv;
}
@Override
public Transform freeze() {
return this;
}
@Override
public TimeStampedPVCoordinates transformPVCoordinates(
final TimeStampedPVCoordinates pv) {
return pv;
}
@Override
public <T extends CalculusFieldElement<T>> FieldPVCoordinates<T>
transformPVCoordinates(final FieldPVCoordinates<T> pv) {
return pv;
}
@Override
public <T extends CalculusFieldElement<T>>
TimeStampedFieldPVCoordinates<T> transformPVCoordinates(
final TimeStampedFieldPVCoordinates<T> pv) {
return pv;
}
/** {@inheritDoc} */
@Override
public void getJacobian(final CartesianDerivativesFilter selector, final double[][] jacobian) {
final int n = 3 * (selector.getMaxOrder() + 1);
for (int i = 0; i < n; ++i) {
Arrays.fill(jacobian[i], 0, n, 0.0);
jacobian[i][i] = 1.0;
}
}
}
}