org.orekit.propagation

Class StateCovariance

java.lang.Object

org.orekit.propagation.StateCovariance

All Implemented Interfaces:

TimeStamped

public class StateCovariance
extends Object
implements TimeStamped

This class is the representation of a covariance matrix at a given date.

Currently, the covariance only represents the orbital elements.

It is possible to change the covariance frame by using the changeCovarianceFrame(Orbit, Frame) or changeCovarianceFrame(Orbit, LOF) method. These methods are based on Equations (18) and (20) of Covariance Transformations for Satellite Flight Dynamics Operations by David A. SVallado.

Finally, covariance orbit type can be changed using the changeCovarianceType(Orbit, OrbitType, PositionAngleType) method.

Since:

11.3

Author:

Bryan Cazabonne, Vincent Cucchietti

Field Summary

Fields

Modifier and Type	Field and Description
static int	STATE_DIMENSION State dimension.

Constructor Summary

Constructors

Constructor and Description
StateCovariance(org.hipparchus.linear.RealMatrix orbitalCovariance, AbsoluteDate epoch, Frame covarianceFrame, OrbitType orbitType, PositionAngleType angleType) Constructor.
StateCovariance(org.hipparchus.linear.RealMatrix orbitalCovariance, AbsoluteDate epoch, LOF lof) Constructor.

Method Summary

Modifier and Type	Method and Description
StateCovariance	changeCovarianceFrame(Orbit orbit, Frame frameOut) Get the covariance in the output frame.
StateCovariance	changeCovarianceFrame(Orbit orbit, LOF lofOut) Get the covariance in a given local orbital frame.
StateCovariance	changeCovarianceType(Orbit orbit, OrbitType outOrbitType, PositionAngleType outAngleType) Get the covariance matrix in another orbit type.
static void	checkFrameAndOrbitTypeConsistency(Frame covarianceFrame, OrbitType inputType) Check constructor's inputs consistency.
AbsoluteDate	getDate() Get the date.
Frame	getFrame() Get the covariance frame.
LOF	getLOF() Get the covariance LOF type.
org.hipparchus.linear.RealMatrix	getMatrix() Get the covariance matrix.
OrbitType	getOrbitType() Get the covariance orbit type.
PositionAngleType	getPositionAngleType() Get the covariance angle type.
static org.hipparchus.linear.RealMatrix	getStm(Orbit initialOrbit, double dt) Get the state transition matrix considering Keplerian contribution only.
StateCovariance	shiftedBy(Orbit orbit, double dt) Get a time-shifted covariance matrix.

Methods inherited from class java.lang.Object

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

Methods inherited from interface org.orekit.time.TimeStamped

durationFrom

Field Detail

STATE_DIMENSION

public static final int STATE_DIMENSION

State dimension.

See Also:

Constant Field Values

Constructor Detail

StateCovariance

public StateCovariance(org.hipparchus.linear.RealMatrix orbitalCovariance,
                       AbsoluteDate epoch,
                       LOF lof)

Constructor.

Parameters:

orbitalCovariance - 6x6 orbital parameters covariance

epoch - epoch of the covariance

lof - covariance LOF type

StateCovariance

public StateCovariance(org.hipparchus.linear.RealMatrix orbitalCovariance,
                       AbsoluteDate epoch,
                       Frame covarianceFrame,
                       OrbitType orbitType,
                       PositionAngleType angleType)

Constructor.

Parameters:

orbitalCovariance - 6x6 orbital parameters covariance

epoch - epoch of the covariance

covarianceFrame - covariance frame (inertial or Earth fixed)

orbitType - orbit type of the covariance (CARTESIAN if covarianceFrame is not pseudo-inertial)

angleType - position angle type of the covariance (not used if orbitType is CARTESIAN)

Method Detail

checkFrameAndOrbitTypeConsistency

public static void checkFrameAndOrbitTypeConsistency(Frame covarianceFrame,
                                                     OrbitType inputType)

Check constructor's inputs consistency.

Parameters:

covarianceFrame - covariance frame (inertial or Earth fixed)

inputType - orbit type of the covariance

Throws:

OrekitException - if input frame is not pseudo-inertial AND the orbit type is not Cartesian

getDate

public AbsoluteDate getDate()

Get the date..

Specified by:

getDate in interface TimeStamped

Returns:

date attached to the object

getMatrix

public org.hipparchus.linear.RealMatrix getMatrix()

Get the covariance matrix.

Returns:

the covariance matrix

getOrbitType

public OrbitType getOrbitType()

Get the covariance orbit type.

Returns:

the covariance orbit type

getPositionAngleType

public PositionAngleType getPositionAngleType()

Get the covariance angle type.

Returns:

the covariance angle type

getFrame

public Frame getFrame()

Get the covariance frame.

Returns:

the covariance frame (can be null)

See Also:

getLOF()

getLOF

public LOF getLOF()

Get the covariance LOF type.

Returns:

the covariance LOF type (can be null)

See Also:

getFrame()

changeCovarianceType

public StateCovariance changeCovarianceType(Orbit orbit,
                                            OrbitType outOrbitType,
                                            PositionAngleType outAngleType)

Get the covariance matrix in another orbit type.

The covariance orbit type cannot be changed if the covariance matrix is expressed in a local orbital frame or a non-pseudo inertial frame.

As this type change uses the jacobian matrix of the transformation, it introduces a linear approximation. Hence, the current covariance matrix will not exactly match the new linearized case and the distribution will not follow a generalized Gaussian distribution anymore.

This is based on equation (1) to (6) from "Vallado, D. A. (2004). Covariance transformations for satellite flight dynamics operations."

Parameters:

orbit - orbit to which the covariance matrix should correspond

outOrbitType - target orbit type of the state covariance matrix

outAngleType - target position angle type of the state covariance matrix

Returns:

a new covariance state, expressed in the target orbit type with the target position angle

See Also:

changeCovarianceFrame(Orbit, Frame)

changeCovarianceFrame

public StateCovariance changeCovarianceFrame(Orbit orbit,
                                             LOF lofOut)

Get the covariance in a given local orbital frame.

Changing the covariance frame is a linear process, this method does not introduce approximation unless a change in covariance orbit type is required.

This is based on equation (18) to (20) "from Vallado, D. A. (2004). Covariance transformations for satellite flight dynamics operations."

Parameters:

orbit - orbit to which the covariance matrix should correspond

lofOut - output local orbital frame

Returns:

a new covariance state, expressed in the output local orbital frame

changeCovarianceFrame

public StateCovariance changeCovarianceFrame(Orbit orbit,
                                             Frame frameOut)

Get the covariance in the output frame.

Changing the covariance frame is a linear process, this method does not introduce approximation unless a change in covariance orbit type is required.

This is based on equation (18) to (20) "from Vallado, D. A. (2004). Covariance transformations for satellite flight dynamics operations."

Parameters:

orbit - orbit to which the covariance matrix should correspond

frameOut - output frame

Returns:

a new covariance state, expressed in the output frame

shiftedBy

public StateCovariance shiftedBy(Orbit orbit,
                                 double dt)

Get a time-shifted covariance matrix.

The shifting model is a linearized, Keplerian one. In other words, it is based on a state transition matrix that is computed assuming Keplerian motion.

Shifting is not intended as a replacement for proper covariance propagation, but should be sufficient for small time shifts or coarse accuracy.

Parameters:

orbit - orbit to which the covariance matrix should correspond

dt - time shift in seconds

Returns:

a new covariance state, shifted with respect to the instance

getStm

public static org.hipparchus.linear.RealMatrix getStm(Orbit initialOrbit,
                                                      double dt)

Get the state transition matrix considering Keplerian contribution only.

Parameters:

initialOrbit - orbit to which the initial covariance matrix should correspond

dt - time difference between the two orbits

Returns:

the state transition matrix used to shift the covariance matrix