AbstractShortTermEncounter2DPOCMethod.java

  1. /* Copyright 2002-2024 CS GROUP
  2.  * Licensed to CS GROUP (CS) under one or more
  3.  * contributor license agreements.  See the NOTICE file distributed with
  4.  * this work for additional information regarding copyright ownership.
  5.  * CS licenses this file to You under the Apache License, Version 2.0
  6.  * (the "License"); you may not use this file except in compliance with
  7.  * the License.  You may obtain a copy of the License at
  8.  *
  9.  *   http://www.apache.org/licenses/LICENSE-2.0
  10.  *
  11.  * Unless required by applicable law or agreed to in writing, software
  12.  * distributed under the License is distributed on an "AS IS" BASIS,
  13.  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  14.  * See the License for the specific language governing permissions and
  15.  * limitations under the License.
  16.  */
  17. package org.orekit.ssa.collision.shorttermencounter.probability.twod;

  19. import org.hipparchus.CalculusFieldElement;
  20. import org.hipparchus.Field;
  21. import org.hipparchus.geometry.euclidean.twod.FieldVector2D;
  22. import org.hipparchus.geometry.euclidean.twod.Vector2D;
  23. import org.hipparchus.linear.FieldMatrix;
  24. import org.hipparchus.linear.RealMatrix;
  25. import org.hipparchus.util.FastMath;
  26. import org.orekit.data.DataContext;
  27. import org.orekit.files.ccsds.ndm.cdm.Cdm;
  28. import org.orekit.files.ccsds.ndm.cdm.CdmData;
  29. import org.orekit.files.ccsds.ndm.cdm.CdmMetadata;
  30. import org.orekit.files.ccsds.ndm.cdm.CdmRelativeMetadata;
  31. import org.orekit.frames.Frame;
  32. import org.orekit.frames.LOFType;
  33. import org.orekit.frames.Transform;
  34. import org.orekit.frames.encounter.EncounterLOFType;
  35. import org.orekit.orbits.CartesianOrbit;
  36. import org.orekit.orbits.FieldOrbit;
  37. import org.orekit.orbits.Orbit;
  38. import org.orekit.propagation.FieldStateCovariance;
  39. import org.orekit.propagation.StateCovariance;
  40. import org.orekit.ssa.metrics.FieldProbabilityOfCollision;
  41. import org.orekit.ssa.metrics.ProbabilityOfCollision;
  42. import org.orekit.time.AbsoluteDate;
  43. import org.orekit.utils.Fieldifier;
  44. import org.orekit.utils.PVCoordinates;

  46. /**
  47.  * This abstract class serves as a foundation to create 2D probability of collision computing method assuming a short term
  48.  * encounter model.
  49.  * <p>
  50.  * All the methods extending this class will at least assume the followings :
  51.  * <ul>
  52.  *     <li>Short term encounter leading to a linear relative motion.</li>
  53.  *     <li>Spherical collision object.</li>
  54.  *     <li>Uncorrelated positional covariance.</li>
  55.  *     <li>Gaussian distribution of the position uncertainties.</li>
  56.  *     <li>Deterministic velocity i.e. no velocity uncertainties.</li>
  57.  * </ul>
  58.  * As listed in the assumptions, methods extending this class are to be used in short encounter,
  59.  * meaning that there must be a high relative velocity. For ease of computation, the resulting swept volume
  60.  * is extended to infinity so that the integral becomes bivariate instead of trivariate (conservative hypothesis).
  61.  * <p>
  62.  * Consequently and if we consider Earth, methods implementing this interface are <u><b>recommended</b></u> for
  63.  * collision happening in Low/Medium Earth Orbit (LEO and MEO) but are <u><b>not recommended</b></u> for collision
  64.  * happening in Geostationary Earth Orbit (GEO).
  65.  *
  66.  * @author Vincent Cucchietti
  67.  * @since 12.0
  68.  */
  69. public abstract class AbstractShortTermEncounter2DPOCMethod implements ShortTermEncounter2DPOCMethod {

  71.     /** Default time of closest approach difference tolerance. */
  72.     public static final double DEFAULT_TCA_DIFFERENCE_TOLERANCE = 1e-6;

  74.     /** Name of the method. */
  75.     private final String name;

  77.     /**
  78.      * Constructor.
  79.      *
  80.      * @param name name of the method
  81.      */
  82.     protected AbstractShortTermEncounter2DPOCMethod(final String name) {
  83.         this.name = name;
  84.     }

  86.     /** {@inheritDoc} */
  87.     public ProbabilityOfCollision compute(final Cdm cdm, final double combinedRadius) {

  89.         final CdmRelativeMetadata cdmRelativeMetadata = cdm.getRelativeMetadata();
  90.         final CdmData             primaryData         = cdm.getDataObject1();
  91.         final CdmData             secondaryData       = cdm.getDataObject2();
  92.         final DataContext         cdmDataContext      = cdm.getDataContext();

  94.         // Extract primary data
  95.         final Orbit primaryOrbit = getObjectOrbitFromCdm(cdmRelativeMetadata, primaryData,
  96.                                                          cdm.getMetadataObject1(), cdmDataContext);
  97.         final StateCovariance primaryCovariance = getObjectStateCovarianceFromCdm(cdmRelativeMetadata, primaryData);

  99.         // Extract secondary data
  100.         final Orbit secondaryOrbit = getObjectOrbitFromCdm(cdmRelativeMetadata, secondaryData,
  101.                                                            cdm.getMetadataObject2(), cdmDataContext);
  102.         final StateCovariance secondaryCovariance = getObjectStateCovarianceFromCdm(cdmRelativeMetadata, secondaryData);

  104.         return compute(primaryOrbit, primaryCovariance, secondaryOrbit, secondaryCovariance, combinedRadius,
  105.                        DEFAULT_ZERO_THRESHOLD);
  106.     }

  108.     /** {@inheritDoc} */
  109.     public <T extends CalculusFieldElement<T>> FieldProbabilityOfCollision<T> compute(final Cdm cdm,
  110.                                                                                       final T combinedRadius,
  111.                                                                                       final double zeroThreshold) {

  113.         final Field<T>            field               = combinedRadius.getField();
  114.         final CdmRelativeMetadata cdmRelativeMetadata = cdm.getRelativeMetadata();
  115.         final CdmData             primaryData         = cdm.getDataObject1();
  116.         final CdmData             secondaryData       = cdm.getDataObject2();
  117.         final CdmMetadata         primaryMetadata     = cdm.getMetadataObject1();
  118.         final CdmMetadata         secondaryMetadata   = cdm.getMetadataObject2();
  119.         final DataContext         cdmDataContext      = cdm.getDataContext();

  121.         // Extract primary data
  122.         final Orbit primaryOrbitFromCdm = getObjectOrbitFromCdm(cdmRelativeMetadata, primaryData,
  123.                 primaryMetadata, cdmDataContext);
  124.         final FieldOrbit<T> primaryOrbit = primaryOrbitFromCdm.getType().convertToFieldOrbit(field,
  125.                 primaryOrbitFromCdm);
  126.         final FieldStateCovariance<T> primaryCovariance =
  127.                 Fieldifier.fieldify(field, getObjectStateCovarianceFromCdm(cdmRelativeMetadata, primaryData));

  129.         // Extract secondary data
  130.         final Orbit secondaryOrbitFromCdm = getObjectOrbitFromCdm(cdmRelativeMetadata, secondaryData,
  131.                 secondaryMetadata, cdmDataContext);
  132.         final FieldOrbit<T> secondaryOrbit = secondaryOrbitFromCdm.getType().convertToFieldOrbit(field,
  133.                 secondaryOrbitFromCdm);
  134.         final FieldStateCovariance<T> secondaryCovariance =
  135.                 Fieldifier.fieldify(field, getObjectStateCovarianceFromCdm(cdmRelativeMetadata, secondaryData));

  137.         return compute(primaryOrbit, primaryCovariance, secondaryOrbit, secondaryCovariance, combinedRadius, zeroThreshold);
  138.     }

  140.     /** {@inheritDoc} */
  141.     public ProbabilityOfCollision compute(final Orbit primaryAtTCA,
  142.                                           final StateCovariance primaryCovariance,
  143.                                           final Orbit secondaryAtTCA,
  144.                                           final StateCovariance secondaryCovariance,
  145.                                           final double combinedRadius,
  146.                                           final double zeroThreshold) {

  148.         final ShortTermEncounter2DDefinition shortTermEncounter2DDefinition = new ShortTermEncounter2DDefinition(
  149.                 primaryAtTCA, primaryCovariance, secondaryAtTCA, secondaryCovariance,
  150.                 combinedRadius, EncounterLOFType.DEFAULT, DEFAULT_TCA_DIFFERENCE_TOLERANCE);

  152.         return compute(shortTermEncounter2DDefinition, zeroThreshold);
  153.     }

  155.     /** {@inheritDoc} */
  156.     public <T extends CalculusFieldElement<T>> FieldProbabilityOfCollision<T> compute(
  157.             final FieldOrbit<T> primaryAtTCA, final FieldStateCovariance<T> primaryCovariance,
  158.             final FieldOrbit<T> secondaryAtTCA, final FieldStateCovariance<T> secondaryCovariance,
  159.             final T combinedRadius, final double zeroThreshold) {

  161.         final FieldShortTermEncounter2DDefinition<T> FieldShortTermEncounter2DDefinition =
  162.                 new FieldShortTermEncounter2DDefinition<>(
  163.                         primaryAtTCA, primaryCovariance, secondaryAtTCA, secondaryCovariance,
  164.                         combinedRadius, EncounterLOFType.DEFAULT, DEFAULT_TCA_DIFFERENCE_TOLERANCE);

  166.         return compute(FieldShortTermEncounter2DDefinition, zeroThreshold);
  167.     }

  169.     /** {@inheritDoc} */
  170.     public ProbabilityOfCollision compute(final ShortTermEncounter2DDefinition encounter,
  171.                                           final double zeroThreshold) {

  173.         final Vector2D otherPositionAfterRotationInCollisionPlane =
  174.                 encounter.computeOtherPositionInRotatedCollisionPlane(zeroThreshold);

  176.         final RealMatrix projectedDiagonalizedCombinedPositionalCovarianceMatrix =
  177.                 encounter.computeProjectedAndDiagonalizedCombinedPositionalCovarianceMatrix();

  179.         return compute(otherPositionAfterRotationInCollisionPlane.getX(),
  180.                        otherPositionAfterRotationInCollisionPlane.getY(),
  181.                        FastMath.sqrt(projectedDiagonalizedCombinedPositionalCovarianceMatrix.getEntry(0, 0)),
  182.                        FastMath.sqrt(projectedDiagonalizedCombinedPositionalCovarianceMatrix.getEntry(1, 1)),
  183.                        encounter.getCombinedRadius());
  184.     }

  186.     /** {@inheritDoc} */
  187.     public <T extends CalculusFieldElement<T>> FieldProbabilityOfCollision<T> compute(
  188.             final FieldShortTermEncounter2DDefinition<T> encounter, final double zeroThreshold) {

  190.         final FieldVector2D<T> otherPositionAfterRotationInCollisionPlane =
  191.                 encounter.computeOtherPositionInRotatedCollisionPlane(zeroThreshold);

  193.         final FieldMatrix<T> projectedDiagonalizedCombinedPositionalCovarianceMatrix =
  194.                 encounter.computeProjectedAndDiagonalizedCombinedPositionalCovarianceMatrix();

  196.         return compute(otherPositionAfterRotationInCollisionPlane.getX(),
  197.                        otherPositionAfterRotationInCollisionPlane.getY(),
  198.                        projectedDiagonalizedCombinedPositionalCovarianceMatrix.getEntry(0, 0).sqrt(),
  199.                        projectedDiagonalizedCombinedPositionalCovarianceMatrix.getEntry(1, 1).sqrt(),
  200.                        encounter.getCombinedRadius());
  201.     }

  203.     /** {@inheritDoc} */
  204.     @Override
  205.     public String getName() {
  206.         return name;
  207.     }

  209.     /** {@inheritDoc} */
  210.     @Override
  211.     public boolean isAMaximumProbabilityOfCollisionMethod() {
  212.         return false;
  213.     }

  215.     /**
  216.      * Extract collision object spacecraft state from given {@link Cdm Conjunction Data Message} data.
  217.      *
  218.      * @param cdmRelativeMetadata conjunction data message relative metadata
  219.      * @param cdmData collision object conjunction data message data
  220.      * @param cdmMetadata collision object conjunction data message metadata
  221.      * @param cdmDataContext conjunction data message data context
  222.      *
  223.      * @return basic collision object spacecraft state from conjunction data message
  224.      */
  225.     protected Orbit getObjectOrbitFromCdm(final CdmRelativeMetadata cdmRelativeMetadata,
  226.                                           final CdmData cdmData,
  227.                                           final CdmMetadata cdmMetadata,
  228.                                           final DataContext cdmDataContext) {

  230.         // Extract orbit
  231.         final Frame        frame = cdmMetadata.getRefFrame().asFrame();
  232.         final AbsoluteDate tca   = cdmRelativeMetadata.getTca();
  233.         final PVCoordinates pvInFrame = new PVCoordinates(cdmData.getStateVectorBlock().getPositionVector(),
  234.                                                           cdmData.getStateVectorBlock().getVelocityVector());
  235.         final double mu = cdmMetadata.getOrbitCenter().getBody().getGM();

  237.         // Simple case where the reference frame is already pseudo-inertial
  238.         if (frame.isPseudoInertial()) {
  239.             return new CartesianOrbit(pvInFrame, frame, tca, mu);
  240.         }
  241.         // Otherwise, convert coordinates to default inertial frame
  242.         final Frame         inertial     = cdmDataContext.getFrames().getGCRF();
  243.         final Transform     toInertial   = frame.getTransformTo(inertial, cdmRelativeMetadata.getTca());
  244.         final PVCoordinates pvInInertial = toInertial.transformPVCoordinates(pvInFrame);

  246.         return new CartesianOrbit(pvInInertial, inertial, tca, mu);
  247.     }

  249.     /**
  250.      * Get collision object state covariance from given {@link Cdm Conjunction Data Message} data.
  251.      *
  252.      * @param cdmRelativeMetadata conjunction data message relative metadata
  253.      * @param cdmData collision object conjunction data message data
  254.      *
  255.      * @return collision object state covariance
  256.      */
  257.     protected StateCovariance getObjectStateCovarianceFromCdm(final CdmRelativeMetadata cdmRelativeMetadata,
  258.                                                               final CdmData cdmData) {
  259.         final AbsoluteDate tca = cdmRelativeMetadata.getTca();
  260.         final RealMatrix rtnCovarianceMatrix =
  261.                 cdmData.getRTNCovarianceBlock().getRTNCovarianceMatrix().getSubMatrix(0, 5, 0, 5);
  262.         return new StateCovariance(rtnCovarianceMatrix, tca, LOFType.QSW_INERTIAL);
  263.     }

  265. }
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