FixedZHomothety.java
/* Copyright 2013-2022 CS GROUP
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* this work for additional information regarding copyright ownership.
* CS licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
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*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
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package org.orekit.rugged.los;
import java.util.stream.Stream;
import org.hipparchus.analysis.differentiation.Derivative;
import org.hipparchus.geometry.euclidean.threed.FieldVector3D;
import org.hipparchus.geometry.euclidean.threed.Vector3D;
import org.hipparchus.util.FastMath;
import org.orekit.rugged.utils.DerivativeGenerator;
import org.orekit.utils.ParameterDriver;
import org.orekit.utils.ParameterObserver;
/** {@link TimeIndependentLOSTransform LOS transform} based on a homothety along the Z axis.
* @author Lucie Labatallee
* @author Guylaine Prat
* @see LOSBuilder
* @since 2.0
*/
public class FixedZHomothety implements TimeIndependentLOSTransform {
/** Parameters scaling factor.
* <p>
* We use a power of 2 to avoid numeric noise introduction
* in the multiplications/divisions sequences.
* </p>
*/
private final double SCALE = FastMath.scalb(1.0, 0);
/** Homothety factor. */
private double factor;
/** Underlying homothety with derivatives. */
private Derivative<?> factorDS;
/** Driver for homothety factor. */
private final ParameterDriver factorDriver;
/** Simple constructor.
* <p>
* The single parameter is the homothety factor.
* </p>
* @param name name of the homothety (used for estimated parameters identification)
* @param factorvalue homothety factor
*/
public FixedZHomothety(final String name, final double factorvalue) {
this.factor = factorvalue;
this.factorDS = null;
this.factorDriver = new ParameterDriver(name, factorvalue, SCALE, 0, Double.POSITIVE_INFINITY);
factorDriver.addObserver(new ParameterObserver() {
@Override
public void valueChanged(final double previousValue, final ParameterDriver driver) {
// reset factor to zero, they will be evaluated lazily if needed
factor = 0.0;
factorDS = null;
}
});
}
/** {@inheritDoc} */
@Override
public Stream<ParameterDriver> getParametersDrivers() {
return Stream.of(factorDriver);
}
/** {@inheritDoc} */
@Override
public Vector3D transformLOS(final int i, final Vector3D los) {
if (factor == 0.0) {
// lazy evaluation of the homothety
factor = factorDriver.getValue();
}
return new Vector3D(los.getX(), los.getY(), factor * los.getZ());
}
/** {@inheritDoc} */
@SuppressWarnings("unchecked")
@Override
public <T extends Derivative<T>> FieldVector3D<T> transformLOS(final int i, final FieldVector3D<T> los,
final DerivativeGenerator<T> generator) {
final T factorD;
if (factorDS == null || !factorDS.getField().equals(generator.getField())) {
// lazy evaluation of the homothety
factorD = generator.variable(factorDriver);
// cache evaluated homothety
factorDS = factorD;
} else {
// reuse cached value
factorD = (T) factorDS;
}
return new FieldVector3D<>(los.getX(), los.getY(), factorD.multiply(los.getZ()));
}
}