Package org.orekit.propagation.covariance

Class StateCovariance

java.lang.Object
org.orekit.propagation.covariance.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 Details

    • STATE_DIMENSION

      public static final int STATE_DIMENSION
      State dimension.
      See Also:

  • Constructor Details

    • StateCovariance

      public StateCovariance(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(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 Details

    • 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

    • inputAndOutputAreIdentical

      public static boolean inputAndOutputAreIdentical(OrbitType inOrbitType, PositionAngleType inAngleType, OrbitType outOrbitType, PositionAngleType outAngleType)
      Checks if input/output orbit and angle types are identical.
      Parameters:
      inOrbitType - input orbit type
      inAngleType - input angle type
      outOrbitType - output orbit type
      outAngleType - output angle type
      Returns:
      flag defining if input/output orbit and angle types are identical

    • inputAndOutputOrbitTypesAreCartesian

      public static boolean inputAndOutputOrbitTypesAreCartesian(OrbitType inOrbitType, OrbitType outOrbitType)
      Checks if input and output orbit types are both OrbitType.CARTESIAN.
      Parameters:
      inOrbitType - input orbit type
      outOrbitType - output orbit type
      Returns:
      flag defining if input and output orbit types are both OrbitType.CARTESIAN

    • getDate

      public AbsoluteDate getDate()
      Get the date..
      Specified by:
      getDate in interface TimeStamped
      Returns:
      date attached to the object

    • getMatrix

      public 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

      public LOF getLOF()
      Get the covariance LOF type.
      Returns:
      the covariance LOF type (can be null)
      See Also:

    • 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

      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