AbstractShortTermEncounter2DPOCMethod.java
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package org.orekit.ssa.collision.shorttermencounter.probability.twod;
import org.hipparchus.CalculusFieldElement;
import org.hipparchus.Field;
import org.hipparchus.geometry.euclidean.twod.FieldVector2D;
import org.hipparchus.geometry.euclidean.twod.Vector2D;
import org.hipparchus.linear.FieldMatrix;
import org.hipparchus.linear.RealMatrix;
import org.hipparchus.util.FastMath;
import org.orekit.data.DataContext;
import org.orekit.files.ccsds.ndm.cdm.Cdm;
import org.orekit.files.ccsds.ndm.cdm.CdmData;
import org.orekit.files.ccsds.ndm.cdm.CdmMetadata;
import org.orekit.files.ccsds.ndm.cdm.CdmRelativeMetadata;
import org.orekit.frames.Frame;
import org.orekit.frames.LOFType;
import org.orekit.frames.Transform;
import org.orekit.frames.encounter.EncounterLOFType;
import org.orekit.orbits.CartesianOrbit;
import org.orekit.orbits.FieldOrbit;
import org.orekit.orbits.Orbit;
import org.orekit.propagation.FieldStateCovariance;
import org.orekit.propagation.StateCovariance;
import org.orekit.ssa.metrics.FieldProbabilityOfCollision;
import org.orekit.ssa.metrics.ProbabilityOfCollision;
import org.orekit.time.AbsoluteDate;
import org.orekit.utils.Fieldifier;
import org.orekit.utils.PVCoordinates;
/**
* This abstract class serves as a foundation to create 2D probability of collision computing method assuming a short term
* encounter model.
* <p>
* All the methods extending this class will at least assume the followings :
* <ul>
* <li>Short term encounter leading to a linear relative motion.</li>
* <li>Spherical collision object.</li>
* <li>Uncorrelated positional covariance.</li>
* <li>Gaussian distribution of the position uncertainties.</li>
* <li>Deterministic velocity i.e. no velocity uncertainties.</li>
* </ul>
* As listed in the assumptions, methods extending this class are to be used in short encounter,
* meaning that there must be a high relative velocity. For ease of computation, the resulting swept volume
* is extended to infinity so that the integral becomes bivariate instead of trivariate (conservative hypothesis).
* <p>
* Consequently and if we consider Earth, methods implementing this interface are <u><b>recommended</b></u> for
* collision happening in Low/Medium Earth Orbit (LEO and MEO) but are <u><b>not recommended</b></u> for collision
* happening in Geostationary Earth Orbit (GEO).
*
* @author Vincent Cucchietti
* @since 12.0
*/
public abstract class AbstractShortTermEncounter2DPOCMethod implements ShortTermEncounter2DPOCMethod {
/** Default time of closest approach difference tolerance. */
public static final double DEFAULT_TCA_DIFFERENCE_TOLERANCE = 1e-6;
/** Name of the method. */
private final String name;
/**
* Constructor.
*
* @param name name of the method
*/
protected AbstractShortTermEncounter2DPOCMethod(final String name) {
this.name = name;
}
/** {@inheritDoc} */
public ProbabilityOfCollision compute(final Cdm cdm, final double combinedRadius) {
final CdmRelativeMetadata cdmRelativeMetadata = cdm.getRelativeMetadata();
final CdmData primaryData = cdm.getDataObject1();
final CdmData secondaryData = cdm.getDataObject2();
final DataContext cdmDataContext = cdm.getDataContext();
// Extract primary data
final Orbit primaryOrbit = getObjectOrbitFromCdm(cdmRelativeMetadata, primaryData,
cdm.getMetadataObject1(), cdmDataContext);
final StateCovariance primaryCovariance = getObjectStateCovarianceFromCdm(cdmRelativeMetadata, primaryData);
// Extract secondary data
final Orbit secondaryOrbit = getObjectOrbitFromCdm(cdmRelativeMetadata, secondaryData,
cdm.getMetadataObject2(), cdmDataContext);
final StateCovariance secondaryCovariance = getObjectStateCovarianceFromCdm(cdmRelativeMetadata, secondaryData);
return compute(primaryOrbit, primaryCovariance, secondaryOrbit, secondaryCovariance, combinedRadius,
DEFAULT_ZERO_THRESHOLD);
}
/** {@inheritDoc} */
public <T extends CalculusFieldElement<T>> FieldProbabilityOfCollision<T> compute(final Cdm cdm,
final T combinedRadius,
final double zeroThreshold) {
final Field<T> field = combinedRadius.getField();
final CdmRelativeMetadata cdmRelativeMetadata = cdm.getRelativeMetadata();
final CdmData primaryData = cdm.getDataObject1();
final CdmData secondaryData = cdm.getDataObject2();
final CdmMetadata primaryMetadata = cdm.getMetadataObject1();
final CdmMetadata secondaryMetadata = cdm.getMetadataObject2();
final DataContext cdmDataContext = cdm.getDataContext();
// Extract primary data
final FieldOrbit<T> primaryOrbit =
Fieldifier.fieldify(field, getObjectOrbitFromCdm(cdmRelativeMetadata, primaryData,
primaryMetadata, cdmDataContext));
final FieldStateCovariance<T> primaryCovariance =
Fieldifier.fieldify(field, getObjectStateCovarianceFromCdm(cdmRelativeMetadata, primaryData));
// Extract secondary data
final FieldOrbit<T> secondaryOrbit =
Fieldifier.fieldify(field, getObjectOrbitFromCdm(cdmRelativeMetadata, secondaryData,
secondaryMetadata, cdmDataContext));
final FieldStateCovariance<T> secondaryCovariance =
Fieldifier.fieldify(field, getObjectStateCovarianceFromCdm(cdmRelativeMetadata, secondaryData));
return compute(primaryOrbit, primaryCovariance, secondaryOrbit, secondaryCovariance, combinedRadius, zeroThreshold);
}
/** {@inheritDoc} */
public ProbabilityOfCollision compute(final Orbit primaryAtTCA,
final StateCovariance primaryCovariance,
final Orbit secondaryAtTCA,
final StateCovariance secondaryCovariance,
final double combinedRadius,
final double zeroThreshold) {
final ShortTermEncounter2DDefinition shortTermEncounter2DDefinition = new ShortTermEncounter2DDefinition(
primaryAtTCA, primaryCovariance, secondaryAtTCA, secondaryCovariance,
combinedRadius, EncounterLOFType.DEFAULT, DEFAULT_TCA_DIFFERENCE_TOLERANCE);
return compute(shortTermEncounter2DDefinition, zeroThreshold);
}
/** {@inheritDoc} */
public <T extends CalculusFieldElement<T>> FieldProbabilityOfCollision<T> compute(
final FieldOrbit<T> primaryAtTCA, final FieldStateCovariance<T> primaryCovariance,
final FieldOrbit<T> secondaryAtTCA, final FieldStateCovariance<T> secondaryCovariance,
final T combinedRadius, final double zeroThreshold) {
final FieldShortTermEncounter2DDefinition<T> FieldShortTermEncounter2DDefinition =
new FieldShortTermEncounter2DDefinition<>(
primaryAtTCA, primaryCovariance, secondaryAtTCA, secondaryCovariance,
combinedRadius, EncounterLOFType.DEFAULT, DEFAULT_TCA_DIFFERENCE_TOLERANCE);
return compute(FieldShortTermEncounter2DDefinition, zeroThreshold);
}
/** {@inheritDoc} */
public ProbabilityOfCollision compute(final ShortTermEncounter2DDefinition encounter,
final double zeroThreshold) {
final Vector2D otherPositionAfterRotationInCollisionPlane =
encounter.computeOtherPositionInRotatedCollisionPlane(zeroThreshold);
final RealMatrix projectedDiagonalizedCombinedPositionalCovarianceMatrix =
encounter.computeProjectedAndDiagonalizedCombinedPositionalCovarianceMatrix();
return compute(otherPositionAfterRotationInCollisionPlane.getX(),
otherPositionAfterRotationInCollisionPlane.getY(),
FastMath.sqrt(projectedDiagonalizedCombinedPositionalCovarianceMatrix.getEntry(0, 0)),
FastMath.sqrt(projectedDiagonalizedCombinedPositionalCovarianceMatrix.getEntry(1, 1)),
encounter.getCombinedRadius());
}
/** {@inheritDoc} */
public <T extends CalculusFieldElement<T>> FieldProbabilityOfCollision<T> compute(
final FieldShortTermEncounter2DDefinition<T> encounter, final double zeroThreshold) {
final FieldVector2D<T> otherPositionAfterRotationInCollisionPlane =
encounter.computeOtherPositionInRotatedCollisionPlane(zeroThreshold);
final FieldMatrix<T> projectedDiagonalizedCombinedPositionalCovarianceMatrix =
encounter.computeProjectedAndDiagonalizedCombinedPositionalCovarianceMatrix();
return compute(otherPositionAfterRotationInCollisionPlane.getX(),
otherPositionAfterRotationInCollisionPlane.getY(),
projectedDiagonalizedCombinedPositionalCovarianceMatrix.getEntry(0, 0).sqrt(),
projectedDiagonalizedCombinedPositionalCovarianceMatrix.getEntry(1, 1).sqrt(),
encounter.getCombinedRadius());
}
/** {@inheritDoc} */
public abstract ProbabilityOfCollision compute(double xm, double ym, double sigmaX, double sigmaY, double radius);
/** {@inheritDoc} */
public abstract <T extends CalculusFieldElement<T>> FieldProbabilityOfCollision<T> compute(T xm, T ym,
T sigmaX, T sigmaY,
T radius);
/** {@inheritDoc} */
@Override
public String getName() {
return name;
}
/** {@inheritDoc} */
@Override
public boolean isAMaximumProbabilityOfCollisionMethod() {
return false;
}
/**
* Extract collision object spacecraft state from given {@link Cdm Conjunction Data Message} data.
*
* @param cdmRelativeMetadata conjunction data message relative metadata
* @param cdmData collision object conjunction data message data
* @param cdmMetadata collision object conjunction data message metadata
* @param cdmDataContext conjunction data message data context
*
* @return basic collision object spacecraft state from conjunction data message
*/
protected Orbit getObjectOrbitFromCdm(final CdmRelativeMetadata cdmRelativeMetadata,
final CdmData cdmData,
final CdmMetadata cdmMetadata,
final DataContext cdmDataContext) {
// Extract orbit
final Frame frame = cdmMetadata.getRefFrame().asFrame();
final AbsoluteDate tca = cdmRelativeMetadata.getTca();
final PVCoordinates pvInFrame = new PVCoordinates(cdmData.getStateVectorBlock().getPositionVector(),
cdmData.getStateVectorBlock().getVelocityVector());
final double mu = cdmMetadata.getOrbitCenter().getBody().getGM();
// Simple case where the reference frame is already pseudo-inertial
if (frame.isPseudoInertial()) {
return new CartesianOrbit(pvInFrame, frame, tca, mu);
}
// Otherwise, convert coordinates to default inertial frame
final Frame inertial = cdmDataContext.getFrames().getGCRF();
final Transform toInertial = frame.getTransformTo(inertial, cdmRelativeMetadata.getTca());
final PVCoordinates pvInInertial = toInertial.transformPVCoordinates(pvInFrame);
return new CartesianOrbit(pvInInertial, inertial, tca, mu);
}
/**
* Get collision object state covariance from given {@link Cdm Conjunction Data Message} data.
*
* @param cdmRelativeMetadata conjunction data message relative metadata
* @param cdmData collision object conjunction data message data
*
* @return collision object state covariance
*/
protected StateCovariance getObjectStateCovarianceFromCdm(final CdmRelativeMetadata cdmRelativeMetadata,
final CdmData cdmData) {
final AbsoluteDate tca = cdmRelativeMetadata.getTca();
final RealMatrix rtnCovarianceMatrix =
cdmData.getRTNCovarianceBlock().getRTNCovarianceMatrix().getSubMatrix(0, 5, 0, 5);
return new StateCovariance(rtnCovarianceMatrix, tca, LOFType.QSW_INERTIAL);
}
}