Package org.orekit.utils

Class PVCoordinates

java.lang.Object

org.orekit.utils.PVCoordinates

All Implemented Interfaces:

Serializable, TimeShiftable<PVCoordinates>

Direct Known Subclasses:

TimeStampedPVCoordinates

public class PVCoordinates
extends Object
implements TimeShiftable<PVCoordinates>, Serializable

Simple container for Position/Velocity/Acceleration triplets.

The state can be slightly shifted to close dates. This shift is based on a simple quadratic model. It is not 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.

This class is the angular counterpart to AngularCoordinates.

Instances of this class are guaranteed to be immutable.

Author:

Fabien Maussion, Luc Maisonobe

See Also:

Serialized Form

Field Summary

Fields

Modifier and Type	Field	Description
static PVCoordinates	ZERO	Fixed position/velocity at origin (both p, v and a are zero vectors).

Constructor Summary

Constructors

Constructor	Description
PVCoordinates()	Simple constructor.
PVCoordinates(double a, PVCoordinates pv)	Multiplicative constructor.
PVCoordinates(double a1, PVCoordinates pv1, double a2, PVCoordinates pv2)	Linear constructor.
PVCoordinates(double a1, PVCoordinates pv1, double a2, PVCoordinates pv2, double a3, PVCoordinates pv3)	Linear constructor.
PVCoordinates(double a1, PVCoordinates pv1, double a2, PVCoordinates pv2, double a3, PVCoordinates pv3, double a4, PVCoordinates pv4)	Linear constructor.
PVCoordinates(FieldVector3D<DerivativeStructure> p)	Builds a PVCoordinates triplet from a FieldVector3D<DerivativeStructure>.
PVCoordinates(Vector3D position, Vector3D velocity)	Builds a PVCoordinates triplet with zero acceleration.
PVCoordinates(Vector3D position, Vector3D velocity, Vector3D acceleration)	Builds a PVCoordinates triplet.
PVCoordinates(PVCoordinates start, PVCoordinates end)	Subtractive constructor.

Method Summary

Modifier and Type	Method	Description
static PVCoordinates	crossProduct(PVCoordinates pv1, PVCoordinates pv2)	Compute the cross-product of two instances.
static Vector3D	estimateVelocity(Vector3D start, Vector3D end, double dt)	Estimate velocity between two positions.
Vector3D	getAcceleration()	Gets the acceleration.
Vector3D	getAngularVelocity()	Get the angular velocity (spin) of this point as seen from the origin.
Vector3D	getMomentum()	Gets the momentum.
Vector3D	getPosition()	Gets the position.
Vector3D	getVelocity()	Gets the velocity.
PVCoordinates	negate()	Get the opposite of the instance.
PVCoordinates	normalize()	Normalize the position part of the instance.
PVCoordinates	shiftedBy(double dt)	Get a time-shifted state.
FieldPVCoordinates<DerivativeStructure>	toDerivativeStructurePV(int order)	Transform the instance to a FieldPVCoordinates<DerivativeStructure>.
FieldVector3D<DerivativeStructure>	toDerivativeStructureVector(int order)	Transform the instance to a FieldVector3D<DerivativeStructure>.
String	toString()	Return a string representation of this position/velocity pair.

Methods inherited from class java.lang.Object

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

Field Detail

ZERO

public static final PVCoordinates ZERO

Fixed position/velocity at origin (both p, v and a are zero vectors).

Constructor Detail

PVCoordinates

public PVCoordinates()

Simple constructor.

Set the Coordinates to default : (0 0 0), (0 0 0), (0 0 0).

PVCoordinates

public PVCoordinates(Vector3D position,
                     Vector3D velocity)

Builds a PVCoordinates triplet with zero acceleration.

Acceleration is set to zero

Parameters:

position - the position vector (m)

velocity - the velocity vector (m/s)

PVCoordinates

public PVCoordinates(Vector3D position,
                     Vector3D velocity,
                     Vector3D acceleration)

Builds a PVCoordinates triplet.

Parameters:

position - the position vector (m)

velocity - the velocity vector (m/s)

acceleration - the acceleration vector (m/s²)

PVCoordinates

public PVCoordinates(double a,
                     PVCoordinates pv)

Multiplicative constructor.

Build a PVCoordinates from another one and a scale factor.

The PVCoordinates built will be a * pv

Parameters:

a - scale factor

pv - base (unscaled) PVCoordinates

PVCoordinates

public PVCoordinates(PVCoordinates start,
                     PVCoordinates end)

Subtractive constructor.

Build a relative PVCoordinates from a start and an end position.

The PVCoordinates built will be end - start.

Parameters:

start - Starting PVCoordinates

end - ending PVCoordinates

PVCoordinates

public PVCoordinates(double a1,
                     PVCoordinates pv1,
                     double a2,
                     PVCoordinates pv2)

Linear constructor.

Build a PVCoordinates from two other ones and corresponding scale factors.

The PVCoordinates built will be a1 * u1 + a2 * u2

Parameters:

a1 - first scale factor

pv1 - first base (unscaled) PVCoordinates

a2 - second scale factor

pv2 - second base (unscaled) PVCoordinates

PVCoordinates

public PVCoordinates(double a1,
                     PVCoordinates pv1,
                     double a2,
                     PVCoordinates pv2,
                     double a3,
                     PVCoordinates pv3)

Linear constructor.

Build a PVCoordinates from three other ones and corresponding scale factors.

The PVCoordinates built will be a1 * u1 + a2 * u2 + a3 * u3

Parameters:

a1 - first scale factor

pv1 - first base (unscaled) PVCoordinates

a2 - second scale factor

pv2 - second base (unscaled) PVCoordinates

a3 - third scale factor

pv3 - third base (unscaled) PVCoordinates

PVCoordinates

public PVCoordinates(double a1,
                     PVCoordinates pv1,
                     double a2,
                     PVCoordinates pv2,
                     double a3,
                     PVCoordinates pv3,
                     double a4,
                     PVCoordinates pv4)

Linear constructor.

Build a PVCoordinates from four other ones and corresponding scale factors.

The PVCoordinates built will be a1 * u1 + a2 * u2 + a3 * u3 + a4 * u4

Parameters:

a1 - first scale factor

pv1 - first base (unscaled) PVCoordinates

a2 - second scale factor

pv2 - second base (unscaled) PVCoordinates

a3 - third scale factor

pv3 - third base (unscaled) PVCoordinates

a4 - fourth scale factor

pv4 - fourth base (unscaled) PVCoordinates

PVCoordinates

public PVCoordinates(FieldVector3D<DerivativeStructure> p)

Builds a PVCoordinates triplet from a FieldVector3D<DerivativeStructure>.

The vector components must have time as their only derivation parameter and have consistent derivation orders.

Parameters:

p - vector with time-derivatives embedded within the coordinates

Method Detail

toDerivativeStructureVector

public FieldVector3D<DerivativeStructure> toDerivativeStructureVector(int order)
                                                               throws OrekitException

Transform the instance to a FieldVector3D<DerivativeStructure>.

The DerivativeStructure coordinates correspond to time-derivatives up to the user-specified order.

Parameters:

order - derivation order for the vector components (must be either 0, 1 or 2)

Returns:

vector with time-derivatives embedded within the coordinates

Throws:

OrekitException - if the user specified order is too large

toDerivativeStructurePV

public FieldPVCoordinates<DerivativeStructure> toDerivativeStructurePV(int order)
                                                                throws OrekitException

Transform the instance to a FieldPVCoordinates<DerivativeStructure>.

The DerivativeStructure coordinates correspond to time-derivatives up to the user-specified order. As both the instance components position, velocity and acceleration and the derivatives of the components holds time-derivatives, there are several ways to retrieve these derivatives. If for example the order is set to 2, then both pv.getPosition().getX().getPartialDerivative(2), pv.getVelocity().getX().getPartialDerivative(1) and pv.getAcceleration().getX().getValue() return the exact same value.

If derivation order is 1, the first derivative of acceleration will be computed as a Keplerian-only jerk. If derivation order is 2, the second derivative of velocity (which is also the first derivative of acceleration) will be computed as a Keplerian-only jerk, and the second derivative of acceleration will be computed as a Keplerian-only jounce.

Parameters:

order - derivation order for the vector components (must be either 0, 1 or 2)

Returns:

pv coordinates with time-derivatives embedded within the coordinates

Throws:

OrekitException - if the user specified order is too large

Since:

9.2

estimateVelocity

public static Vector3D estimateVelocity(Vector3D start,
                                        Vector3D end,
                                        double dt)

Estimate velocity between two positions.

Estimation is based on a simple fixed velocity translation during the time interval between the two positions.

Parameters:

start - start position

end - end position

dt - time elapsed between the dates of the two positions

Returns:

velocity allowing to go from start to end positions

shiftedBy

public PVCoordinates shiftedBy(double dt)

Get a time-shifted state.

The state can be slightly shifted to close dates. This shift is based on a simple Taylor expansion. It is not 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.

Specified by:

shiftedBy in interface TimeShiftable<PVCoordinates>

Parameters:

dt - time shift in seconds

Returns:

a new state, shifted with respect to the instance (which is immutable)

getPosition

public Vector3D getPosition()

Gets the position.

Returns:

the position vector (m).

getVelocity

public Vector3D getVelocity()

Gets the velocity.

Returns:

the velocity vector (m/s).

getAcceleration

public Vector3D getAcceleration()

Gets the acceleration.

Returns:

the acceleration vector (m/s²).

getMomentum

public Vector3D getMomentum()

Gets the momentum.

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.

The returned vector is recomputed each time this method is called, it is not cached.

Returns:

a new instance of the momentum vector (m²/s).

getAngularVelocity

public Vector3D getAngularVelocity()

Get the angular velocity (spin) of this point as seen from the origin.

The angular velocity vector is parallel to the angular momentum and is computed by ω = p × v / ||p||²

Returns:

the angular velocity vector

See Also:

Angular Velocity on Wikipedia

negate

public PVCoordinates negate()

Get the opposite of the instance.

Returns:

a new position-velocity which is opposite to the instance

normalize

public PVCoordinates normalize()

Normalize the position part of the instance.

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).

Returns:

a new instance, with first component normalized and remaining component computed to have consistent derivatives

crossProduct

public static PVCoordinates crossProduct(PVCoordinates pv1,
                                         PVCoordinates pv2)

Compute the cross-product of two instances.

Parameters:

pv1 - first instances

pv2 - second instances

Returns:

the cross product v1 ^ v2 as a new instance

toString

public String toString()

Return a string representation of this position/velocity pair.

Overrides:

toString in class Object

Returns:

string representation of this position/velocity pair