org.orekit.utils

Class PVCoordinates

java.lang.Object

org.orekit.utils.PVCoordinates

All Implemented Interfaces:

Serializable, TimeShiftable<PVCoordinates>

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

Simple container for Position/Velocity pairs.

The state can be slightly shifted to close dates. This shift is based on a simple linear 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 and Description
static PVCoordinates	ZERO Fixed position/velocity at origin (both p and v are zero vectors).

Constructor Summary

Constructors

Constructor and 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(PVCoordinates start, PVCoordinates end) Subtractive constructor
PVCoordinates(Vector3D position, Vector3D velocity) Builds a PVCoordinates pair.

Method Summary

Methods

Modifier and Type	Method and Description
static Vector3D	estimateVelocity(Vector3D start, Vector3D end, double dt) Estimate velocity between two positions.
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.
static PVCoordinates	interpolate(AbsoluteDate date, boolean useVelocities, Collection<Pair<AbsoluteDate,PVCoordinates>> sample) Interpolate position-velocity.
PVCoordinates	negate() Get the opposite of the instance.
PVCoordinates	shiftedBy(double dt) Get a time-shifted state.
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 and v are zero vectors).

Constructor Detail

PVCoordinates

public PVCoordinates()

Simple constructor.

Sets the Coordinates to default : (0 0 0) (0 0 0).

PVCoordinates

public PVCoordinates(Vector3D position,
             Vector3D velocity)

Builds a PVCoordinates pair.

Parameters:

position - the position vector (m)

velocity - the velocity vector (m/s)

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

Method Detail

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 linear 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.

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)

interpolate

public static PVCoordinates interpolate(AbsoluteDate date,
                        boolean useVelocities,
                        Collection<Pair<AbsoluteDate,PVCoordinates>> sample)

Interpolate position-velocity.

The interpolated instance is created by polynomial Hermite interpolation ensuring velocity remains the exact derivative of position.

Note that even if first time derivatives (velocities) 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.

Parameters:

date - interpolation date

useVelocities - if true, use sample points velocities, otherwise ignore them and use only positions

sample - sample points on which interpolation should be done

Returns:

a new position-velocity, interpolated at specified date

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).

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

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