Frame.java
/* Copyright 2002-2015 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.frames;
import java.io.Serializable;
import org.orekit.errors.OrekitException;
import org.orekit.errors.OrekitMessages;
import org.orekit.time.AbsoluteDate;
/** Tridimensional references frames class.
*
* <h5> Frame Presentation </h5>
* <p>This class is the base class for all frames in OREKIT. The frames are
* linked together in a tree with some specific frame chosen as the root of the tree.
* Each frame is defined by {@link Transform transforms} combining any number
* of translations and rotations from a reference frame which is its
* parent frame in the tree structure.</p>
* <p>When we say a {@link Transform transform} t is <em>from frame<sub>A</sub>
* to frame<sub>B</sub></em>, we mean that if the coordinates of some absolute
* vector (say the direction of a distant star for example) has coordinates
* u<sub>A</sub> in frame<sub>A</sub> and u<sub>B</sub> in frame<sub>B</sub>,
* then u<sub>B</sub>={@link
* Transform#transformVector(org.apache.commons.math3.geometry.euclidean.threed.Vector3D)
* t.transformVector(u<sub>A</sub>)}.
* <p>The transforms may be constant or varying, depending on the implementation of
* the {@link TransformProvider transform provider} used to define the frame. For simple
* fixed transforms, using {@link FixedTransformProvider} is sufficient. For varying
* transforms (time-dependent or telemetry-based for example), it may be useful to define
* specific implementations of {@link TransformProvider transform provider}.</p>
*
* @author Guylaine Prat
* @author Luc Maisonobe
* @author Pascal Parraud
*/
public class Frame implements Serializable {
/** Serializable UID. */
private static final long serialVersionUID = -6981146543760234087L;
/** Parent frame (only the root frame doesn't have a parent). */
private final Frame parent;
/** Depth of the frame with respect to tree root. */
private final int depth;
/** Provider for transform from parent frame to instance. */
private final TransformProvider transformProvider;
/** Instance name. */
private final String name;
/** Indicator for pseudo-inertial frames. */
private final boolean pseudoInertial;
/** Private constructor used only for the root frame.
* @param name name of the frame
* @param pseudoInertial true if frame is considered pseudo-inertial
* (i.e. suitable for propagating orbit)
*/
private Frame(final String name, final boolean pseudoInertial) {
parent = null;
depth = 0;
transformProvider = new FixedTransformProvider(Transform.IDENTITY);
this.name = name;
this.pseudoInertial = pseudoInertial;
}
/** Build a non-inertial frame from its transform with respect to its parent.
* <p>calling this constructor is equivalent to call
* <code>{link {@link #Frame(Frame, Transform, String, boolean)
* Frame(parent, transform, name, false)}</code>.</p>
* @param parent parent frame (must be non-null)
* @param transform transform from parent frame to instance
* @param name name of the frame
* @exception IllegalArgumentException if the parent frame is null
*/
public Frame(final Frame parent, final Transform transform, final String name)
throws IllegalArgumentException {
this(parent, transform, name, false);
}
/** Build a non-inertial frame from its transform with respect to its parent.
* <p>calling this constructor is equivalent to call
* <code>{link {@link #Frame(Frame, Transform, String, boolean)
* Frame(parent, transform, name, false)}</code>.</p>
* @param parent parent frame (must be non-null)
* @param transformProvider provider for transform from parent frame to instance
* @param name name of the frame
* @exception IllegalArgumentException if the parent frame is null
*/
public Frame(final Frame parent, final TransformProvider transformProvider, final String name)
throws IllegalArgumentException {
this(parent, transformProvider, name, false);
}
/** Build a frame from its transform with respect to its parent.
* <p>The convention for the transform is that it is from parent
* frame to instance. This means that the two following frames
* are similar:</p>
* <pre>
* Frame frame1 = new Frame(FramesFactory.getGCRF(), new Transform(t1, t2));
* Frame frame2 = new Frame(new Frame(FramesFactory.getGCRF(), t1), t2);
* </pre>
* @param parent parent frame (must be non-null)
* @param transform transform from parent frame to instance
* @param name name of the frame
* @param pseudoInertial true if frame is considered pseudo-inertial
* (i.e. suitable for propagating orbit)
* @exception IllegalArgumentException if the parent frame is null
*/
public Frame(final Frame parent, final Transform transform, final String name,
final boolean pseudoInertial)
throws IllegalArgumentException {
this(parent, new FixedTransformProvider(transform), name, pseudoInertial);
}
/** Build a frame from its transform with respect to its parent.
* <p>The convention for the transform is that it is from parent
* frame to instance. This means that the two following frames
* are similar:</p>
* <pre>
* Frame frame1 = new Frame(FramesFactory.getGCRF(), new Transform(t1, t2));
* Frame frame2 = new Frame(new Frame(FramesFactory.getGCRF(), t1), t2);
* </pre>
* @param parent parent frame (must be non-null)
* @param transformProvider provider for transform from parent frame to instance
* @param name name of the frame
* @param pseudoInertial true if frame is considered pseudo-inertial
* (i.e. suitable for propagating orbit)
* @exception IllegalArgumentException if the parent frame is null
*/
public Frame(final Frame parent, final TransformProvider transformProvider, final String name,
final boolean pseudoInertial)
throws IllegalArgumentException {
if (parent == null) {
throw OrekitException.createIllegalArgumentException(OrekitMessages.NULL_PARENT_FOR_FRAME,
name);
}
this.parent = parent;
this.depth = parent.depth + 1;
this.transformProvider = transformProvider;
this.name = name;
this.pseudoInertial = pseudoInertial;
}
/** Get the name.
* @return the name
*/
public String getName() {
return this.name;
}
/** Check if the frame is pseudo-inertial.
* <p>Pseudo-inertial frames are frames that do have a linear motion and
* either do not rotate or rotate at a very low rate resulting in
* neglectible inertial forces. This means they are suitable for orbit
* definition and propagation using Newtonian mechanics. Frames that are
* <em>not</em> pseudo-inertial are <em>not</em> suitable for orbit
* definition and propagation.</p>
* @return true if frame is pseudo-inertial
*/
public boolean isPseudoInertial() {
return pseudoInertial;
}
/** New definition of the java.util toString() method.
* @return the name
*/
public String toString() {
return this.name;
}
/** Get the parent frame.
* @return parent frame
*/
public Frame getParent() {
return parent;
}
/** Get the depth of the frame.
* <p>
* The depth of a frame is the number of parents frame between
* it and the frames tree root. It is 0 for the root frame, and
* the depth of a frame is the depth of its parent frame plus one.
* </p>
* @return depth of the frame
*/
public int getDepth() {
return depth;
}
/** Get the n<sup>th</sup> ancestor of the frame.
* @param n index of the ancestor (0 is the instance, 1 is its parent,
* 2 is the parent of its parent...)
* @return n<sup>th</sup> ancestor of the frame (must be between 0
* and the depth of the frame)
* @exception IllegalArgumentException if n is larger than the depth
* of the instance
*/
public Frame getAncestor(final int n) throws IllegalArgumentException {
// safety check
if (n > depth) {
throw OrekitException.createIllegalArgumentException(OrekitMessages.FRAME_NO_NTH_ANCESTOR,
name, depth, n);
}
// go upward to find ancestor
Frame current = this;
for (int i = 0; i < n; ++i) {
current = current.parent;
}
return current;
}
/** Get the transform from the instance to another frame.
* @param destination destination frame to which we want to transform vectors
* @param date the date (can be null if it is sure than no date dependent frame is used)
* @return transform from the instance to the destination frame
* @exception OrekitException if some frame specific error occurs
*/
public Transform getTransformTo(final Frame destination, final AbsoluteDate date)
throws OrekitException {
if (this == destination) {
// shortcut for special case that may be frequent
return Transform.IDENTITY;
}
// common ancestor to both frames in the frames tree
final Frame common = findCommon(this, destination);
// transform from common to instance
Transform commonToInstance = Transform.IDENTITY;
for (Frame frame = this; frame != common; frame = frame.parent) {
commonToInstance =
new Transform(date, frame.transformProvider.getTransform(date), commonToInstance);
}
// transform from destination up to common
Transform commonToDestination = Transform.IDENTITY;
for (Frame frame = destination; frame != common; frame = frame.parent) {
commonToDestination =
new Transform(date, frame.transformProvider.getTransform(date), commonToDestination);
}
// transform from instance to destination via common
return new Transform(date, commonToInstance.getInverse(), commonToDestination);
}
/** Get the provider for transform from parent frame to instance.
* @return provider for transform from parent frame to instance
*/
public TransformProvider getTransformProvider() {
return transformProvider;
}
/** Find the deepest common ancestor of two frames in the frames tree.
* @param from origin frame
* @param to destination frame
* @return an ancestor frame of both <code>from</code> and <code>to</code>
*/
private static Frame findCommon(final Frame from, final Frame to) {
// select deepest frames that could be the common ancestor
Frame currentF = from.depth > to.depth ? from.getAncestor(from.depth - to.depth) : from;
Frame currentT = from.depth > to.depth ? to : to.getAncestor(to.depth - from.depth);
// go upward until we find a match
while (currentF != currentT) {
currentF = currentF.parent;
currentT = currentT.parent;
}
return currentF;
}
/** Determine if a Frame is a child of another one.
* @param potentialAncestor supposed ancestor frame
* @return true if the potentialAncestor belongs to the
* path from instance to the root frame, excluding itself
*/
public boolean isChildOf(final Frame potentialAncestor) {
if (depth <= potentialAncestor.depth) {
return false;
}
return getAncestor(depth - potentialAncestor.depth) == potentialAncestor;
}
/** Get the unique root frame.
* @return the unique instance of the root frame
*/
protected static Frame getRoot() {
return LazyRootHolder.INSTANCE;
}
/** Get a new version of the instance, frozen with respect to a reference frame.
* <p>
* Freezing a frame consist in computing its position and orientation with respect
* to another frame at some freezing date and fixing them so they do not depend
* on time anymore. This means the frozen frame is fixed with respect to the
* reference frame.
* </p>
* <p>
* One typical use of this method is to compute an inertial launch reference frame
* by freezing a {@link TopocentricFrame topocentric frame} at launch date
* with respect to an inertial frame. Another use is to freeze an equinox-related
* celestial frame at a reference epoch date.
* </p>
* <p>
* Only the frame returned by this method is frozen, the instance by itself
* is not affected by calling this method and still moves freely.
* </p>
* @param reference frame with respect to which the instance will be frozen
* @param freezingDate freezing date
* @param frozenName name of the frozen frame
* @return a frozen version of the instance
* @exception OrekitException if transform between reference frame and instance
* cannot be computed at freezing frame
*/
public Frame getFrozenFrame(final Frame reference, final AbsoluteDate freezingDate,
final String frozenName) throws OrekitException {
return new Frame(reference, reference.getTransformTo(this, freezingDate).freeze(),
frozenName, reference.isPseudoInertial());
}
// We use the Initialization on demand holder idiom to store
// the singletons, as it is both thread-safe, efficient (no
// synchronization) and works with all versions of java.
/** Holder for the root frame singleton. */
private static class LazyRootHolder {
/** Unique instance. */
private static final Frame INSTANCE = new Frame("GCRF", true) {
/** Serializable UID. */
private static final long serialVersionUID = -2654403496396721543L;
/** Replace the instance with a data transfer object for serialization.
* <p>
* This intermediate class serializes nothing.
* </p>
* @return data transfer object that will be serialized
*/
private Object writeReplace() {
return new DataTransferObject();
}
};
/** Private constructor.
* <p>This class is a utility class, it should neither have a public
* nor a default constructor. This private constructor prevents
* the compiler from generating one automatically.</p>
*/
private LazyRootHolder() {
}
}
/** Internal class used only for serialization. */
private static class DataTransferObject implements Serializable {
/** Serializable UID. */
private static final long serialVersionUID = 4067764035816491212L;
/** Simple constructor.
*/
private DataTransferObject() {
}
/** Replace the deserialized data transfer object with a {@link FactoryManagedFrame}.
* @return replacement {@link FactoryManagedFrame}
*/
private Object readResolve() {
return getRoot();
}
}
}