Alfriend1999Max.java
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package org.orekit.ssa.collision.shorttermencounter.probability.twod;
import org.hipparchus.CalculusFieldElement;
import org.hipparchus.util.FastMath;
/**
* Compute the probability of collision assuming the worst case described in : "Kyle Alfriend, Maruthi Akella, Joseph
* Frisbee, James Foster, Deok-Jin Lee, and Matthew Wilkins. Probability of ProbabilityOfCollision Error Analysis. Space
* Debris, 1(1):21–35, 1999.".
* <p>It assumes:
* <ul>
* <li>Short 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>
* <li>Both objects are in circular orbits (eq 14).</li>
* <li>Probability density function is constant over the collision circle (eq 18).</li>
* <li>Covariance multiplied by a coefficient KSquared = MahalanobisDistanceSquared / 2 (eq 19-20).</li>
* </ul>
* <p>
* By assuming a constant probability density function over the collision circle this method will,
* <b>most of the time</b>, give much higher probability of collision than other regular methods.
* That is why it is qualified as a maximum probability of collision computing method.
*
* @author Vincent Cucchietti
* @see <a href="https://en.wikipedia.org/wiki/Mahalanobis_distance">Mahalanobis distance.</a>
* @since 12.0
*/
public class Alfriend1999Max extends AbstractAlfriend1999 {
/** Empty constructor. */
public Alfriend1999Max() {
super(ShortTermEncounter2DPOCMethodType.ALFRIEND_1999_MAX.name());
}
/**
* Compute the value of the probability of collision.
*
* @param radius sum of primary and secondary collision object equivalent sphere radii (m)
* @param squaredMahalanobisDistance squared Mahalanobis distance
* @param covarianceMatrixDeterminant covariance matrix determinant
*
* @return value of the probability of collision
*/
@Override
public double computeValue(final double radius, final double squaredMahalanobisDistance,
final double covarianceMatrixDeterminant) {
return radius * radius / (squaredMahalanobisDistance * FastMath.sqrt(covarianceMatrixDeterminant) * FastMath.E);
}
/**
* Compute the value of the probability of collision.
*
* @param radius sum of primary and secondary collision object equivalent sphere radii (m)
* @param squaredMahalanobisDistance squared Mahalanobis distance
* @param covarianceMatrixDeterminant covariance matrix determinant
* @param <T> type of the field elements
*
* @return value of the probability of collision
*/
@Override
public <T extends CalculusFieldElement<T>> T computeValue(final T radius, final T squaredMahalanobisDistance,
final T covarianceMatrixDeterminant) {
return radius.multiply(radius).divide(squaredMahalanobisDistance.multiply(covarianceMatrixDeterminant.sqrt())
.multiply(FastMath.E));
}
/** {@inheritDoc} */
@Override
public boolean isAMaximumProbabilityOfCollisionMethod() {
return true;
}
/** {@inheritDoc} */
@Override
public ShortTermEncounter2DPOCMethodType getType() {
return ShortTermEncounter2DPOCMethodType.ALFRIEND_1999_MAX;
}
}