agi.foundation.propagators

(agi.foundation.models-2025r1.jar)

Class TwoBodyPropagator

java.lang.Object

agi.foundation.infrastructure.DefinitionalObject

agi.foundation.propagators.CartesianOnePointPropagator

agi.foundation.propagators.TwoBodyPropagator

All Implemented Interfaces:

ICloneWithContext, IEnumerateDependencies, IEquatableDefinition, IFreezable

public final class TwoBodyPropagator
extends CartesianOnePointPropagator

Propagates an orbit using a simple two-body model.

Constructor Summary

Constructors

Constructor and Description
TwoBodyPropagator(JulianDate orbitEpoch, ReferenceFrame referenceFrame, DelaunayElements elements) Initializes a new instance.
TwoBodyPropagator(JulianDate orbitEpoch, ReferenceFrame referenceFrame, EquinoctialElements elements) Initializes a new instance.
TwoBodyPropagator(JulianDate orbitEpoch, ReferenceFrame referenceFrame, KeplerianElements elements) Initializes a new instance.
TwoBodyPropagator(JulianDate orbitEpoch, ReferenceFrame referenceFrame, ModifiedKeplerianElements elements) Initializes a new instance.
TwoBodyPropagator(JulianDate orbitEpoch, ReferenceFrame referenceFrame, Motion1<Cartesian> initialConditions, double gravitationalParameter) Initializes a new instance.

Method Summary

Modifier and Type	Method and Description
protected boolean	checkForSameDefinition(CartesianOnePointPropagator other) Checks to determine if another instance has the same definition as this instance and returns true if it does.
Object	clone(CopyContext context) Clones this object using the specified context.
protected int	computeCurrentDefinitionHashCode() Computes a hash code based on the current properties of this object.
void	enumerateDependencies(DependencyEnumerator enumerator) Enumerates the dependencies of this object by calling DependencyEnumerator#enumerate(T) for each object that this object directly depends upon.
MotionEvaluator1<Cartesian>	getEvaluator(EvaluatorGroup group) Gets an evaluator that can propagate at individual dates.
double	getGravitationalParameter() Gets the gravitational parameter for the central body around which to propagate.
Motion1<Cartesian>	getInitialConditions() Gets the orbital elements from which to propagate.
protected ReferenceFrame	getMotionReferenceFrame() Gets the reference frame in which the motion is defined.
JulianDate	getOrbitEpoch() Gets the Julian date at which the InitialConditions (get / set) of the orbit are defined.
ReferenceFrame	getReferenceFrame() Gets the reference frame in which the ephemeris is produced.
void	setInitialConditions(Motion1<Cartesian> value) Sets the orbital elements from which to propagate.
void	setOrbitEpoch(JulianDate value) Sets the Julian date at which the InitialConditions (get / set) of the orbit are defined.
void	setReferenceFrame(ReferenceFrame value) Sets the reference frame in which the ephemeris is produced.

Methods inherited from class agi.foundation.propagators.CartesianOnePointPropagator

checkForSameDefinition, createPoint, getEvaluator, propagate, propagate

Methods inherited from class agi.foundation.infrastructure.DefinitionalObject

areSameDefinition, areSameDefinition, areSameDefinition, areSameDefinition, areSameDefinition, collectionItemsAreSameDefinition, collectionItemsAreSameDefinition, collectionItemsAreSameDefinition, dictionaryItemsAreSameDefinition, freeze, freezeAggregatedObjects, getCollectionHashCode, getCollectionHashCode, getCollectionHashCode, getDefinitionHashCode, getDefinitionHashCode, getDefinitionHashCode, getDefinitionHashCode, getDefinitionHashCode, getDefinitionHashCode, getDictionaryHashCode, getIsFrozen, isSameDefinition, throwIfFrozen

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

TwoBodyPropagator

public TwoBodyPropagator(@Nonnull
                         JulianDate orbitEpoch,
                         ReferenceFrame referenceFrame,
                         @Nonnull
                         Motion1<Cartesian> initialConditions,
                         double gravitationalParameter)

Initializes a new instance.

For correct results, referenceFrame generally must be an inertial reference frame. However, it is easy to obtain ephemeris in any desired ReferenceFrame (get / set) (such as the FixedFrame (get / set)) by transforming it after it has been produced by the propagator. To do so, call CartesianOnePointPropagator.propagate(JulianDate,JulianDate,Duration,int,agi.foundation.geometry.ReferenceFrame). Or, call CartesianOnePointPropagator.createPoint() and then use GeometryTransformer.observePoint(Point,agi.foundation.geometry.ReferenceFrame) to get an evaluator that can be used to find the propagated position in the specified reference frame.

Parameters:

orbitEpoch - The Julian date at which the initial conditions are defined.

referenceFrame - The reference frame in which the initialConditions are defined. Generally this should be the InertialFrame (get / set) of the central body around which you are propagating. See the Remarks section for more information.

initialConditions - The elements from which to propagate.

gravitationalParameter - The gravitational parameter for the central body around which to propagate.

Throws:

ArgumentException - Thrown when the initialConditions do not contain velocity information.

TwoBodyPropagator

public TwoBodyPropagator(@Nonnull
                         JulianDate orbitEpoch,
                         ReferenceFrame referenceFrame,
                         @Nonnull
                         KeplerianElements elements)

Initializes a new instance.

For correct results, referenceFrame generally must be an inertial reference frame. However, it is easy to obtain ephemeris in any desired ReferenceFrame (get / set) (such as the FixedFrame (get / set)) by transforming it after it has been produced by the propagator. To do so, call CartesianOnePointPropagator.propagate(JulianDate,JulianDate,Duration,int,agi.foundation.geometry.ReferenceFrame). Or, call CartesianOnePointPropagator.createPoint() and then use GeometryTransformer.observePoint(Point,agi.foundation.geometry.ReferenceFrame) to get an evaluator that can be used to find the propagated position in the specified reference frame.

Parameters:

orbitEpoch - The Julian date at which the initial conditions are defined.

referenceFrame - The reference frame in which the elements are defined. Generally this should be the InertialFrame (get / set) of the central body around which you are propagating. See the Remarks section for more information.

elements - The elements from which to propagate.

TwoBodyPropagator

public TwoBodyPropagator(@Nonnull
                         JulianDate orbitEpoch,
                         ReferenceFrame referenceFrame,
                         @Nonnull
                         ModifiedKeplerianElements elements)

Initializes a new instance.

For correct results, referenceFrame generally must be an inertial reference frame. However, it is easy to obtain ephemeris in any desired ReferenceFrame (get / set) (such as the FixedFrame (get / set)) by transforming it after it has been produced by the propagator. To do so, call CartesianOnePointPropagator.propagate(JulianDate,JulianDate,Duration,int,agi.foundation.geometry.ReferenceFrame). Or, call CartesianOnePointPropagator.createPoint() and then use GeometryTransformer.observePoint(Point,agi.foundation.geometry.ReferenceFrame) to get an evaluator that can be used to find the propagated position in the specified reference frame.

Parameters:

orbitEpoch - The Julian date at which the initial conditions are defined.

referenceFrame - The reference frame in which the elements are defined. Generally this should be the InertialFrame (get / set) of the central body around which you are propagating. See the Remarks section for more information.

elements - The elements from which to propagate.

TwoBodyPropagator

public TwoBodyPropagator(@Nonnull
                         JulianDate orbitEpoch,
                         ReferenceFrame referenceFrame,
                         @Nonnull
                         EquinoctialElements elements)

Initializes a new instance.

For correct results, referenceFrame generally must be an inertial reference frame. However, it is easy to obtain ephemeris in any desired ReferenceFrame (get / set) (such as the FixedFrame (get / set)) by transforming it after it has been produced by the propagator. To do so, call CartesianOnePointPropagator.propagate(JulianDate,JulianDate,Duration,int,agi.foundation.geometry.ReferenceFrame). Or, call CartesianOnePointPropagator.createPoint() and then use GeometryTransformer.observePoint(Point,agi.foundation.geometry.ReferenceFrame) to get an evaluator that can be used to find the propagated position in the specified reference frame.

Parameters:

orbitEpoch - The Julian date at which the initial conditions are defined.

referenceFrame - The reference frame in which the elements are defined. Generally this should be the InertialFrame (get / set) of the central body around which you are propagating. See the Remarks section for more information.

elements - The elements from which to propagate.

TwoBodyPropagator

public TwoBodyPropagator(@Nonnull
                         JulianDate orbitEpoch,
                         ReferenceFrame referenceFrame,
                         @Nonnull
                         DelaunayElements elements)

Initializes a new instance.

For correct results, referenceFrame generally must be an inertial reference frame. However, it is easy to obtain ephemeris in any desired ReferenceFrame (get / set) (such as the FixedFrame (get / set)) by transforming it after it has been produced by the propagator. To do so, call CartesianOnePointPropagator.propagate(JulianDate,JulianDate,Duration,int,agi.foundation.geometry.ReferenceFrame). Or, call CartesianOnePointPropagator.createPoint() and then use GeometryTransformer.observePoint(Point,agi.foundation.geometry.ReferenceFrame) to get an evaluator that can be used to find the propagated position in the specified reference frame.

Parameters:

orbitEpoch - The Julian date at which the initial conditions are defined.

referenceFrame - The reference frame in which the elements are defined. Generally this should be the InertialFrame (get / set) of the central body around which you are propagating. See the Remarks section for more information.

elements - The elements from which to propagate.

Method Detail

clone

public Object clone(CopyContext context)

Clones this object using the specified context.

This method should be implemented to call a copy constructor on the class of the object being cloned. The copy constructor should take the CopyContext as a parameter in addition to the existing instance to copy. The copy constructor should first call CopyContext.addObjectMapping(T, T) to identify the newly constructed instance as a copy of the existing instance. It should then copy all fields, using CopyContext.updateReference(T) to copy any reference fields.

A typical implementation of ICloneWithContext:

public static class MyClass implements ICloneWithContext {
    public MyClass(MyClass existingInstance, CopyContext context) {
        context.addObjectMapping(existingInstance, this);
        someReference = context.updateReference(existingInstance.someReference);
    }

    @Override
    public final Object clone(CopyContext context) {
        return new MyClass(this, context);
    }

    private Object someReference;
}

In general, all fields that are reference types should be copied with a call to CopyContext.updateReference(T). There are a couple of exceptions:

1. Fields that are aggregate parts of the object should always be copied. A referenced object is an aggregate if properties or methods on the object being copied can modify the externally-visible value of the referenced object.
2. If the semantics of the referenced object require that it have a single parent, owner, context, etc., and the object being copied is that parent, owner, or context, then the referenced object should always be copied.

If one of these exceptions applies, the CopyContext should be given an opportunity to update the reference before the reference is copied explicitly. Use CopyContext.updateReference(T) to update the reference. If CopyContext.updateReference(T) returns the original object, indicating that the context does not have a replacement registered, then copy the object manually by invoking a Clone method, a copy constructor, or by manually constructing a new instance and copying the values.

alwaysCopy = context.updateReference(existingInstance.alwaysCopy);
if (existingInstance.alwaysCopy != null && alwaysCopy == existingInstance.alwaysCopy) {
    alwaysCopy = (AlwaysCopy) existingInstance.alwaysCopy.clone(context);
}

If you are implementing an evaluator (a class that implements IEvaluator), the IEvaluator.updateEvaluatorReferences(agi.foundation.infrastructure.CopyContext) method shares some responsibilities with the copy context constructor. Code duplication can be avoided by doing the following:

1. For references to other evaluators ONLY, simply assign the reference in the constructor instead of calling CopyContext.updateReference(T). You should still call CopyContext.updateReference(T) on any references to non-evaluators.
2. Call IEvaluator.updateEvaluatorReferences(agi.foundation.infrastructure.CopyContext) as the last line in the constructor and pass it the same CopyContext passed to the constructor.
3. Implement IEvaluator.updateEvaluatorReferences(agi.foundation.infrastructure.CopyContext) as normal. See the reference documentation for IEvaluator.updateEvaluatorReferences(agi.foundation.infrastructure.CopyContext) for more information on implementing that method.

public MyClass(MyClass existingInstance, CopyContext context) {
    super(existingInstance, context);
    someReference = context.updateReference(existingInstance.someReference);
    evaluatorReference = existingInstance.evaluatorReference;
    updateEvaluatorReferences(context);
}

@Override
public void updateEvaluatorReferences(CopyContext context) {
    evaluatorReference = context.updateReference(evaluatorReference);
}

@Override
public Object clone(CopyContext context) {
    return new MyClass(this, context);
}

private Object someReference;
private IEvaluator evaluatorReference;

Specified by:

clone in interface ICloneWithContext

Specified by:

clone in class DefinitionalObject

Parameters:

context - The context to use to perform the copy.

Returns:

A new instance which is a copy of this object.

checkForSameDefinition

protected boolean checkForSameDefinition(CartesianOnePointPropagator other)

Checks to determine if another instance has the same definition as this instance and returns true if it does. Derived classes MUST override this method and check all new fields introduced by the derived class for definitional equivalence. It is NOT necessary to check base class fields because the base class will already have done that. When overriding this method, you should NOT call the base implementation because it will return false for all derived-class instances. Derived classes should check the type of other to preserve the symmetric nature of IEquatableDefinition.isSameDefinition(java.lang.Object).

Specified by:

checkForSameDefinition in class CartesianOnePointPropagator

Parameters:

other - The other instance to compare to this one.

Returns:

true if the two objects are defined equivalently; otherwise false.

computeCurrentDefinitionHashCode

protected int computeCurrentDefinitionHashCode()

Computes a hash code based on the current properties of this object. Derived classes MUST override this method and compute a hash code that combines: a unique hash code seed, the base implementation result, and the hash codes of all new fields introduced by the derived class which are used in the TwoBodyPropagator.checkForSameDefinition(agi.foundation.propagators.CartesianOnePointPropagator) method.

Overrides:

computeCurrentDefinitionHashCode in class CartesianOnePointPropagator

Returns:

The computed hash code.

enumerateDependencies

public void enumerateDependencies(DependencyEnumerator enumerator)

Enumerates the dependencies of this object by calling DependencyEnumerator#enumerate(T) for each object that this object directly depends upon. Derived classes which contain additional dependencies MUST override this method, call the base implementation, and enumerate dependencies introduced by the derived class.

Specified by:

enumerateDependencies in interface IEnumerateDependencies

Overrides:

enumerateDependencies in class DefinitionalObject

Parameters:

enumerator - The enumerator that is informed of the dependencies of this object.

getEvaluator

public MotionEvaluator1<Cartesian> getEvaluator(EvaluatorGroup group)

Gets an evaluator that can propagate at individual dates.

This evaluator propagates the orbit state from InitialConditions (get / set) at OrbitEpoch (get / set) based on the GravitationalParameter (get). The result of evaluating will be a Motion<Cartesian> corresponding to the orbital position and velocity at the given JulianDate expressed in the propagator's ReferenceFrame (get / set).

Specified by:

getEvaluator in class CartesianOnePointPropagator

Parameters:

group - The group with which to associate the new evaluator. By grouping evaluators that are often evaluated at the same Julian dates, common computations can be performed only once for the entire group instead of multiple times for each evaluator.

Returns:

The evaluator.

See Also:

CartesianOnePointPropagator.createPoint()

getMotionReferenceFrame

protected ReferenceFrame getMotionReferenceFrame()

Gets the reference frame in which the motion is defined.

Specified by:

getMotionReferenceFrame in class CartesianOnePointPropagator

Returns:

The reference frame.

getOrbitEpoch

@Nonnull
public final JulianDate getOrbitEpoch()

Gets the Julian date at which the InitialConditions (get / set) of the orbit are defined.

setOrbitEpoch

public final void setOrbitEpoch(@Nonnull
                                JulianDate value)

Sets the Julian date at which the InitialConditions (get / set) of the orbit are defined.

getReferenceFrame

public final ReferenceFrame getReferenceFrame()

Gets the reference frame in which the ephemeris is produced.

setReferenceFrame

public final void setReferenceFrame(ReferenceFrame value)

Sets the reference frame in which the ephemeris is produced.

getInitialConditions

@Nonnull
public final Motion1<Cartesian> getInitialConditions()

Gets the orbital elements from which to propagate.

setInitialConditions

public final void setInitialConditions(@Nonnull
                                       Motion1<Cartesian> value)

Sets the orbital elements from which to propagate.

getGravitationalParameter

public final double getGravitationalParameter()

Gets the gravitational parameter for the central body around which to propagate.