java.lang.Object
- org.orekit.ssa.collision.shorttermencounter.probability.twod.ShortTermEncounter2DDefinition

```
public class ShortTermEncounter2DDefinition
extends Object
```
Defines the encounter between two collision object at time of closest approach assuming a short-term encounter model . It uses the given encounter frame type to define the encounter.
Both the primary and secondary collision object can be at the reference of the encounter frame, it is up to the user to choose.
The "reference" object is the object considered at the reference of the given encounter frame while the "other" object is the one not placed at the reference.
For example, if the user wants the primary to be at the reference of the default encounter frame, they will have to input data in the following manner:
```
 final ShortTermEncounter2DDefinition encounter = new ShortTermEncounter2DDefinition(primaryOrbitAtTCA, primaryCovariance, primaryRadius, secondaryOrbitAtTCA, secondaryCovariance, secondaryRadius);
  
 
```
However, if the user wants to put the secondary at the reference and use the Valsecchi encounter frame, they will have to type :
```
 final ShortTermEncounter2DDefinition encounter = new ShortTermEncounter2DDefinition(secondaryOrbitAtTCA, secondaryCovariance, secondaryRadius, primaryOrbitAtTCA, primaryCovariance, primaryRadius, EncounterLOFType.VALSECCHI_2003);
  
 
```
Note that in the current implementation, the shape of the collision objects is assumed to be a sphere.
Since:

12.0

Author:

Vincent Cucchietti

Constructor Summary

Constructors
Constructor	Description
`ShortTermEncounter2DDefinition(Orbit referenceAtTCA, StateCovariance referenceCovariance, double referenceRadius, Orbit otherAtTCA, StateCovariance otherCovariance, double otherRadius)`	Constructor.
`ShortTermEncounter2DDefinition(Orbit referenceAtTCA, StateCovariance referenceCovariance, double referenceRadius, Orbit otherAtTCA, StateCovariance otherCovariance, double otherRadius, EncounterLOFType encounterFrameType, double tcaTolerance)`	Constructor.
`ShortTermEncounter2DDefinition(Orbit referenceAtTCA, StateCovariance referenceCovariance, Orbit otherAtTCA, StateCovariance otherCovariance, double combinedRadius)`	Constructor.
`ShortTermEncounter2DDefinition(Orbit referenceAtTCA, StateCovariance referenceCovariance, Orbit otherAtTCA, StateCovariance otherCovariance, double combinedRadius, EncounterLOFType encounterFrameType, double tcaTolerance)`	Constructor.

Method Summary

All Methods Static Methods Instance Methods Concrete Methods
Modifier and Type	Method	Description
`StateCovariance`	`computeCombinedCovarianceInEncounterFrame()`	Compute the combined covariance expressed in the encounter frame.
`StateCovariance`	`computeCombinedCovarianceInReferenceTNW()`	Takes both covariance matrices (expressed in their respective RTN local orbital frame) from reference and other collision object with which this instance was created and sum them in the reference collision object TNW local orbital frame.
`double`	`computeCoppolaEncounterDuration()`	Compute the Encounter duration (s) evaluated using Coppola's formula described in : "COPPOLA, Vincent, et al.
`double`	`computeMahalanobisDistance()`	Compute the Mahalanobis distance computed with the other collision object projected onto the collision plane (commonly called B-Plane) and expressed in the rotated encounter frame (frame in which the combined covariance matrix is diagonalized, see `computeEncounterPlaneRotationMatrix(double)` for more details).
`double`	`computeMahalanobisDistance(double zeroThreshold)`	Compute the Mahalanobis distance computed with the other collision object projected onto the collision plane (commonly called B-Plane) and expressed in the rotated encounter frame (frame in which the combined covariance matrix is diagonalized, see `computeEncounterPlaneRotationMatrix(double)` for more details).
`double`	`computeMissDistance()`	Compute the miss distance at time of closest approach.
`Vector2D`	`computeOtherPositionInCollisionPlane()`	Compute the other collision object `position` projected onto the collision plane.
`Vector2D`	`computeOtherPositionInRotatedCollisionPlane()`	Compute the other collision object `position` in the rotated collision plane.
`Vector2D`	`computeOtherPositionInRotatedCollisionPlane(double zeroThreshold)`	Compute the other collision object `position` in the rotated collision plane.
`PVCoordinates`	`computeOtherRelativeToReferencePVInReferenceInertial()`	Compute the other collision position and velocity relative to the reference collision object.
`RealMatrix`	`computeProjectedAndDiagonalizedCombinedPositionalCovarianceMatrix()`	Compute the combined covariance matrix diagonalized and projected onto the collision plane.
`RealMatrix`	`computeProjectedCombinedPositionalCovarianceMatrix()`	Compute the projected combined covariance matrix onto the collision plane.
`RealMatrix`	`computeReferenceInertialToCollisionPlaneProjectionMatrix()`	Compute the projection matrix from the reference collision object inertial frame to the collision plane.
`double`	`computeSquaredMahalanobisDistance()`	Compute the squared Mahalanobis distance computed with the other collision object projected onto the collision plane (commonly called B-Plane) and expressed in the rotated encounter frame (frame in which the combined covariance matrix is diagonalized, see `computeEncounterPlaneRotationMatrix(double)` for more details).
`double`	`computeSquaredMahalanobisDistance(double zeroThreshold)`	Compute the squared Mahalanobis distance computed with the other collision object projected onto the collision plane (commonly called B-Plane) and expressed in the rotated encounter frame (frame in which the combined covariance matrix is diagonalized, see `computeEncounterPlaneRotationMatrix(double)` for more details).
`static double`	`computeSquaredMahalanobisDistance(double xm, double ym, double sigmaX, double sigmaY)`	Compute the squared Mahalanobis distance.
`static double`	`computeSquaredMahalanobisDistance(Vector2D otherPosition, RealMatrix covarianceMatrix)`	Compute the squared Mahalanobis distance.
`double`	`getCombinedRadius()`	Get combined radius.
`EncounterLOF`	`getEncounterFrame()`	Get encounter local orbital frame.
`Orbit`	`getOtherAtTCA()`	Get other's orbit at time of closest approach.
`StateCovariance`	`getOtherCovariance()`	Get other's covariance.
`Orbit`	`getReferenceAtTCA()`	Get reference's orbit at time of closest approach.
`StateCovariance`	`getReferenceCovariance()`	Get reference's covariance.
`AbsoluteDate`	`getTca()`	Get the Time of Closest Approach.

Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

- Constructor Detail
  - ShortTermEncounter2DDefinition
```
public ShortTermEncounter2DDefinition(Orbit referenceAtTCA,
                                      StateCovariance referenceCovariance,
                                      double referenceRadius,
                                      Orbit otherAtTCA,
                                      StateCovariance otherCovariance,
                                      double otherRadius)
```
    Constructor.
    
    Parameters:
    
    referenceAtTCA - reference collision object orbit at time of closest approach
    
    referenceCovariance - reference collision object covariance matrix in its respective RTN frame
    
    referenceRadius - reference collision's equivalent sphere radius
    
    otherAtTCA - other collision object orbit at time of closest approach
    
    otherCovariance - other collision object covariance matrix in its respective RTN frame
    
    otherRadius - other collision's equivalent sphere radius
    
    Throws:
    
    OrekitException - If both collision object spacecraft state don't have the same definition date.
  - ShortTermEncounter2DDefinition
```
public ShortTermEncounter2DDefinition(Orbit referenceAtTCA,
                                      StateCovariance referenceCovariance,
                                      Orbit otherAtTCA,
                                      StateCovariance otherCovariance,
                                      double combinedRadius)
```
    Constructor.
    
    Parameters:
    
    referenceAtTCA - reference collision object orbit at time of closest approach
    
    referenceCovariance - reference collision object covariance matrix in its respective RTN frame
    
    otherAtTCA - other collision object orbit at time of closest approach
    
    otherCovariance - other collision object covariance matrix in its respective RTN frame
    
    combinedRadius - combined radius (m)
    
    Throws:
    
    OrekitException - If both collision object spacecraft state don't have the same definition date.
  - ShortTermEncounter2DDefinition
```
public ShortTermEncounter2DDefinition(Orbit referenceAtTCA,
                                      StateCovariance referenceCovariance,
                                      double referenceRadius,
                                      Orbit otherAtTCA,
                                      StateCovariance otherCovariance,
                                      double otherRadius,
                                      EncounterLOFType encounterFrameType,
                                      double tcaTolerance)
```
    Constructor.
    
    Parameters:
    
    referenceAtTCA - reference collision object orbit at time of closest approach
    
    referenceCovariance - reference collision object covariance matrix in its respective RTN frame
    
    referenceRadius - reference collision's equivalent sphere radius
    
    otherAtTCA - other collision object orbit at time of closest approach
    
    otherCovariance - other collision object covariance matrix in its respective RTN frame
    
    otherRadius - other collision's equivalent sphere radius
    
    encounterFrameType - type of encounter frame to use
    
    tcaTolerance - tolerance on reference and other times of closest approach difference
    
    Throws:
    
    OrekitException - If both collision object spacecraft state don't have the same definition date.
  - ShortTermEncounter2DDefinition
```
public ShortTermEncounter2DDefinition(Orbit referenceAtTCA,
                                      StateCovariance referenceCovariance,
                                      Orbit otherAtTCA,
                                      StateCovariance otherCovariance,
                                      double combinedRadius,
                                      EncounterLOFType encounterFrameType,
                                      double tcaTolerance)
```
    Constructor.
    
    Parameters:
    
    referenceAtTCA - reference collision object orbit at time of closest approach
    
    referenceCovariance - reference collision object covariance matrix in its respective RTN frame
    
    otherAtTCA - other collision object orbit at time of closest approach
    
    otherCovariance - other collision object covariance matrix in its respective RTN frame
    
    combinedRadius - combined radius (m)
    
    encounterFrameType - type of encounter frame to use
    
    tcaTolerance - tolerance on reference and other times of closest approach difference
    
    Throws:
    
    OrekitException - If both collision object spacecraft state don't have the same definition date.
- Method Detail
  - computeSquaredMahalanobisDistance
```
public static double computeSquaredMahalanobisDistance(double xm,
                                                       double ym,
                                                       double sigmaX,
                                                       double sigmaY)
```
    Compute the squared Mahalanobis distance.
    
    Parameters:
    
    xm - other collision object projected xm position onto the collision plane in the rotated encounter frame
    
    ym - other collision object projected ym position onto the collision plane in the rotated encounter frame
    
    sigmaX - square root of the x-axis eigen value of the diagonalized combined covariance matrix projected onto the collision plane
    
    sigmaY - square root of the y-axis eigen value of the diagonalized combined covariance matrix projected onto the collision plane
    
    Returns:
    
    squared Mahalanobis distance
  - computeSquaredMahalanobisDistance
```
public static double computeSquaredMahalanobisDistance(Vector2D otherPosition,
                                                       RealMatrix covarianceMatrix)
```
    Compute the squared Mahalanobis distance.
    
    Parameters:
    
    otherPosition - other collision object projected position onto the collision plane in the rotated encounter frame
    
    covarianceMatrix - combined covariance matrix projected onto the collision plane and diagonalized
    
    Returns:
    
    squared Mahalanobis distance
  - computeOtherRelativeToReferencePVInReferenceInertial
```
public PVCoordinates computeOtherRelativeToReferencePVInReferenceInertial()
```
    Compute the other collision position and velocity relative to the reference collision object. Expressed in the reference collision object inertial frame.
    
    Returns:
    
    other collision position and velocity relative to the reference collision object, expressed in the reference collision object inertial frame.
  - computeReferenceInertialToCollisionPlaneProjectionMatrix
```
public RealMatrix computeReferenceInertialToCollisionPlaneProjectionMatrix()
```
    Compute the projection matrix from the reference collision object inertial frame to the collision plane.
    Note that this matrix will only rotate from the reference collision object inertial frame to the encounter frame and project onto the collision plane, this is only a rotation.
    
    Returns:
    
    projection matrix from the reference collision object inertial frame to the collision plane
  - computeProjectedAndDiagonalizedCombinedPositionalCovarianceMatrix
```
public RealMatrix computeProjectedAndDiagonalizedCombinedPositionalCovarianceMatrix()
```
    Compute the combined covariance matrix diagonalized and projected onto the collision plane.
    Diagonalize projected positional covariance matrix in a specific manner to have σ_xx² ≤ σ_yy².
    
    Returns:
    
    combined covariance matrix diagonalized and projected onto the collision plane
  - computeProjectedCombinedPositionalCovarianceMatrix
```
public RealMatrix computeProjectedCombinedPositionalCovarianceMatrix()
```
    Compute the projected combined covariance matrix onto the collision plane.
    
    Returns:
    
    projected combined covariance matrix onto the collision plane
  - computeCombinedCovarianceInEncounterFrame
```
public StateCovariance computeCombinedCovarianceInEncounterFrame()
```
    Compute the combined covariance expressed in the encounter frame.
    
    Returns:
    
    combined covariance expressed in the encounter frame
  - computeOtherPositionInCollisionPlane
```
public Vector2D computeOtherPositionInCollisionPlane()
```
    Compute the other collision object position projected onto the collision plane.
    
    Returns:
    
    other collision object position projected onto the collision plane
  - computeOtherPositionInRotatedCollisionPlane
```
public Vector2D computeOtherPositionInRotatedCollisionPlane()
```
    Compute the other collision object position in the rotated collision plane.
    Uses a default zero threshold of 1e-15.
    The coordinates are often noted xm and ym in probability of collision related papers.
    
    The mentioned rotation concerns the rotation that diagonalize the combined covariance matrix inside the collision plane.
    
    Returns:
    
    other collision object position in the rotated collision plane
  - computeOtherPositionInRotatedCollisionPlane
```
public Vector2D computeOtherPositionInRotatedCollisionPlane(double zeroThreshold)
```
    Compute the other collision object position in the rotated collision plane.
    The coordinates are often noted xm and ym in probability of collision related papers.
    The mentioned rotation concerns the rotation that diagonalize the combined covariance matrix inside the collision plane.
    
    Parameters:
    
    zeroThreshold - threshold below which values are considered equal to zero
    
    Returns:
    
    other collision object position in the rotated collision plane
  - computeCoppolaEncounterDuration
```
public double computeCoppolaEncounterDuration()
```
    Compute the Encounter duration (s) evaluated using Coppola's formula described in : "COPPOLA, Vincent, et al. Evaluating the short encounter assumption of the probability of collision formula. 2012."
    This method is to be used to check the validity of the short-term encounter model. The user is expected to compare the computed duration with the orbital period from both objects and draw its own conclusions.
    It uses γ = 1e-16 as the resolution of a double is nearly 1e-16 so γ smaller than that are not meaningful to compute.
    
    Returns:
    
    encounter duration (s) evaluated using Coppola's formula
  - computeMissDistance
```
public double computeMissDistance()
```
    Compute the miss distance at time of closest approach.
    
    Returns:
    
    miss distance
  - computeMahalanobisDistance
```
public double computeMahalanobisDistance()
```
    Compute the Mahalanobis distance computed with the other collision object projected onto the collision plane (commonly called B-Plane) and expressed in the rotated encounter frame (frame in which the combined covariance matrix is diagonalized, see computeEncounterPlaneRotationMatrix(double) for more details).
    Uses a default zero threshold of 1e-15 for the computation of the diagonalizing of the projected covariance matrix.
    
    Returns:
    
    Mahalanobis distance between the reference and other collision object
    
    See Also:
    
    Mahalanobis distance
  - computeMahalanobisDistance
```
public double computeMahalanobisDistance(double zeroThreshold)
```
    Compute the Mahalanobis distance computed with the other collision object projected onto the collision plane (commonly called B-Plane) and expressed in the rotated encounter frame (frame in which the combined covariance matrix is diagonalized, see computeEncounterPlaneRotationMatrix(double) for more details).
    
    Parameters:
    
    zeroThreshold - threshold below which values are considered equal to zero
    
    Returns:
    
    Mahalanobis distance between the reference and other collision object
    
    See Also:
    
    Mahalanobis distance
  - computeSquaredMahalanobisDistance
```
public double computeSquaredMahalanobisDistance()
```
    Compute the squared Mahalanobis distance computed with the other collision object projected onto the collision plane (commonly called B-Plane) and expressed in the rotated encounter frame (frame in which the combined covariance matrix is diagonalized, see computeEncounterPlaneRotationMatrix(double) for more details).
    Uses a default zero threshold of 1e-15 for the computation of the diagonalizing of the projected covariance matrix.
    
    Returns:
    
    squared Mahalanobis distance between the reference and other collision object
    
    See Also:
    
    Mahalanobis distance
  - computeSquaredMahalanobisDistance
```
public double computeSquaredMahalanobisDistance(double zeroThreshold)
```
    Compute the squared Mahalanobis distance computed with the other collision object projected onto the collision plane (commonly called B-Plane) and expressed in the rotated encounter frame (frame in which the combined covariance matrix is diagonalized, see computeEncounterPlaneRotationMatrix(double) for more details).
    
    Parameters:
    
    zeroThreshold - threshold below which values are considered equal to zero
    
    Returns:
    
    squared Mahalanobis distance between the reference and other collision object
    
    See Also:
    
    Mahalanobis distance
  - computeCombinedCovarianceInReferenceTNW
```
public StateCovariance computeCombinedCovarianceInReferenceTNW()
```
    Takes both covariance matrices (expressed in their respective RTN local orbital frame) from reference and other collision object with which this instance was created and sum them in the reference collision object TNW local orbital frame.
    
    Returns:
    
    combined covariance matrix expressed in the reference collision object TNW local orbital frame
  - getTca
```
public AbsoluteDate getTca()
```
    Get the Time of Closest Approach.
    Commonly called TCA.
    
    Returns:
    
    time of closest approach
  - getReferenceAtTCA
```
public Orbit getReferenceAtTCA()
```
    Get reference's orbit at time of closest approach.
    
    Returns:
    
    reference's orbit at time of closest approach
  - getOtherAtTCA
```
public Orbit getOtherAtTCA()
```
    Get other's orbit at time of closest approach.
    
    Returns:
    
    other's orbit at time of closest approach
  - getReferenceCovariance
```
public StateCovariance getReferenceCovariance()
```
    Get reference's covariance.
    
    Returns:
    
    reference's covariance
  - getOtherCovariance
```
public StateCovariance getOtherCovariance()
```
    Get other's covariance.
    
    Returns:
    
    other's covariance
  - getCombinedRadius
```
public double getCombinedRadius()
```
    Get combined radius.
    
    Returns:
    
    combined radius (m)
  - getEncounterFrame
```
public EncounterLOF getEncounterFrame()
```
    Get encounter local orbital frame.
    
    Returns:
    
    encounter local orbital frame

Class ShortTermEncounter2DDefinition

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

Constructor Detail

ShortTermEncounter2DDefinition

ShortTermEncounter2DDefinition

ShortTermEncounter2DDefinition

ShortTermEncounter2DDefinition

Method Detail

computeSquaredMahalanobisDistance

computeSquaredMahalanobisDistance

computeOtherRelativeToReferencePVInReferenceInertial

computeReferenceInertialToCollisionPlaneProjectionMatrix

computeProjectedAndDiagonalizedCombinedPositionalCovarianceMatrix

computeProjectedCombinedPositionalCovarianceMatrix

computeCombinedCovarianceInEncounterFrame

computeOtherPositionInCollisionPlane

computeOtherPositionInRotatedCollisionPlane

computeOtherPositionInRotatedCollisionPlane

computeCoppolaEncounterDuration

computeMissDistance

computeMahalanobisDistance

computeMahalanobisDistance

computeSquaredMahalanobisDistance

computeSquaredMahalanobisDistance

computeCombinedCovarianceInReferenceTNW

getTca

getReferenceAtTCA

getOtherAtTCA

getReferenceCovariance

getOtherCovariance

getCombinedRadius

getEncounterFrame