QuadraticClockModel.java
/* Copyright 2002-2024 Thales Alenia Space
* Licensed to CS GROUP (CS) under one or more
* contributor license agreements. See the NOTICE file distributed with
* 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.estimation.measurements;
import org.hipparchus.CalculusFieldElement;
import org.hipparchus.analysis.differentiation.Gradient;
import org.hipparchus.util.FastMath;
import org.orekit.errors.OrekitException;
import org.orekit.errors.OrekitMessages;
import org.orekit.time.AbsoluteDate;
import org.orekit.time.ClockModel;
import org.orekit.time.ClockOffset;
import org.orekit.time.FieldAbsoluteDate;
import org.orekit.time.FieldClockOffset;
import org.orekit.utils.ParameterDriver;
import java.util.Map;
/** Quadratic clock model.
*
* @author Luc Maisonobe
* @since 12.1
*
*/
public class QuadraticClockModel implements ClockModel {
/** Clock offset scaling factor.
* <p>
* We use a power of 2 to avoid numeric noise introduction
* in the multiplications/divisions sequences.
* </p>
*/
private static final double CLOCK_OFFSET_SCALE = FastMath.scalb(1.0, -10);
/** Constant term. */
private final ParameterDriver a0;
/** Linear term. */
private final ParameterDriver a1;
/** Quadratic term. */
private final ParameterDriver a2;
/** Simple constructor.
* @param referenceDate reference date
* @param a0 constant term
* @param a1 linear term
* @param a2 quadratic term
*/
public QuadraticClockModel(final AbsoluteDate referenceDate,
final double a0, final double a1, final double a2) {
this(new ParameterDriver("a0",
0.0, CLOCK_OFFSET_SCALE,
Double.NEGATIVE_INFINITY, Double.POSITIVE_INFINITY),
new ParameterDriver("a1",
0.0, CLOCK_OFFSET_SCALE,
Double.NEGATIVE_INFINITY, Double.POSITIVE_INFINITY),
new ParameterDriver("a2",
0.0, CLOCK_OFFSET_SCALE,
Double.NEGATIVE_INFINITY, Double.POSITIVE_INFINITY));
this.a0.setValue(a0);
this.a0.setReferenceDate(referenceDate);
this.a1.setValue(a1);
this.a1.setReferenceDate(referenceDate);
this.a2.setValue(a2);
this.a2.setReferenceDate(referenceDate);
}
/** Simple constructor.
* @param a0 constant term
* @param a1 linear term
* @param a2 quadratic term
*/
public QuadraticClockModel(final ParameterDriver a0, final ParameterDriver a1, final ParameterDriver a2) {
this.a0 = a0;
this.a1 = a1;
this.a2 = a2;
}
/** {@inheritDoc} */
@Override
public AbsoluteDate getValidityStart() {
return AbsoluteDate.PAST_INFINITY;
}
/** {@inheritDoc} */
@Override
public AbsoluteDate getValidityEnd() {
return AbsoluteDate.FUTURE_INFINITY;
}
/** {@inheritDoc} */
@Override
public ClockOffset getOffset(final AbsoluteDate date) {
final double dt = date.durationFrom(getSafeReference(date));
final double c0 = a0.getValue(date);
final double c1 = a1.getValue(date);
final double c2 = a2.getValue(date);
return new ClockOffset(date,
(c2 * dt + c1) * dt + c0,
2 * c2 * dt + c1,
2 * c2);
}
/** {@inheritDoc} */
@Override
public <T extends CalculusFieldElement<T>> FieldClockOffset<T> getOffset(final FieldAbsoluteDate<T> date) {
final AbsoluteDate aDate = date.toAbsoluteDate();
final T dt = date.durationFrom(getSafeReference(aDate));
final double c0 = a0.getValue(aDate);
final double c1 = a1.getValue(aDate);
final double c2 = a2.getValue(aDate);
return new FieldClockOffset<>(date,
dt.multiply(dt.multiply(c2).add(c1)).add(c0),
dt.multiply(2 * c2).add(c1),
dt.newInstance(2 * c2));
}
/** Get a safe reference date.
* <p>
* This method deals with parameters drivers for which no reference
* date has been set, which is acceptable if the model is not
* time-dependent.
* </p>
* @param date date at which values are requested
* @return safe reference date
*/
private AbsoluteDate getSafeReference(final AbsoluteDate date) {
if (a0.getReferenceDate() == null) {
if (a1.getValue(date) == 0 && a2.getValue(date) == 0) {
// it is OK to not have a reference date is clock offset is constant
return date;
} else {
throw new OrekitException(OrekitMessages.NO_REFERENCE_DATE_FOR_PARAMETER,
a0.getName());
}
} else {
return a0.getReferenceDate();
}
}
/** Convert to gradient model.
* @param freeParameters total number of free parameters in the gradient
* @param indices indices of the differentiation parameters in derivatives computations,
* must be span name and not driver name
* @param date date at which model must be valid
* @return converted clock model
*/
public QuadraticFieldClockModel<Gradient> toGradientModel(final int freeParameters,
final Map<String, Integer> indices,
final AbsoluteDate date) {
final Gradient g0 = a0.getValue(freeParameters, indices, date);
final Gradient g1 = a1.getValue(freeParameters, indices, date);
final Gradient g2 = a2.getValue(freeParameters, indices, date);
final FieldAbsoluteDate<Gradient> referenceDate =
new FieldAbsoluteDate<>(g0.getField(), getSafeReference(date));
return new QuadraticFieldClockModel<>(referenceDate, g0, g1, g2);
}
}