org.orekit.utils

Class SecularAndHarmonic

java.lang.Object

org.orekit.utils.SecularAndHarmonic

public class SecularAndHarmonic
extends Object

Class for fitting evolution of osculating orbital parameters.

This class allows conversion from osculating parameters to mean parameters.

Author:

Luc Maisonobe

Constructor Summary

Constructors

Constructor and Description
SecularAndHarmonic(int secularDegree, double... pulsations) Simple constructor.

Method Summary

Modifier and Type	Method and Description
void	addPoint(AbsoluteDate date, double osculatingValue) Add a fitting point.
double[]	approximateAsPolynomialOnly(int combinedDegree, AbsoluteDate combinedReference, int meanDegree, int meanHarmonics, AbsoluteDate start, AbsoluteDate end, double step) Approximate an already fitted model to polynomial only terms.
void	fit() Fit parameters.
double[]	getFittedParameters() Get a copy of the last fitted parameters.
double	getHarmonicAmplitude() Get an upper bound of the fitted harmonic amplitude.
AbsoluteDate	getReferenceDate() Get the reference date.
double	meanDerivative(AbsoluteDate date, int degree, int harmonics) Get mean derivative, truncated to first components.
double	meanSecondDerivative(AbsoluteDate date, int degree, int harmonics) Get mean second derivative, truncated to first components.
double	meanValue(AbsoluteDate date, int degree, int harmonics) Get mean value, truncated to first components.
double	osculatingDerivative(AbsoluteDate date) Get fitted osculating derivative.
double	osculatingSecondDerivative(AbsoluteDate date) Get fitted osculating second derivative.
double	osculatingValue(AbsoluteDate date) Get fitted osculating value.
void	resetFitting(AbsoluteDate date, double... initialGuess) Reset fitting.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

SecularAndHarmonic

public SecularAndHarmonic(int secularDegree,
                          double... pulsations)

Simple constructor.

Parameters:

secularDegree - degree of polynomial secular part

pulsations - pulsations of harmonic part

Method Detail

resetFitting

public void resetFitting(AbsoluteDate date,
                         double... initialGuess)

Reset fitting.

Parameters:

date - reference date

initialGuess - initial guess for the parameters

See Also:

getReferenceDate()

addPoint

public void addPoint(AbsoluteDate date,
                     double osculatingValue)

Add a fitting point.

Parameters:

date - date of the point

osculatingValue - osculating value

getReferenceDate

public AbsoluteDate getReferenceDate()

Get the reference date.

Returns:

reference date

See Also:

resetFitting(AbsoluteDate, double...)

getHarmonicAmplitude

public double getHarmonicAmplitude()

Get an upper bound of the fitted harmonic amplitude.

Returns:

upper bound of the fitted harmonic amplitude

fit

public void fit()

Fit parameters.

See Also:

getFittedParameters()

getFittedParameters

public double[] getFittedParameters()

Get a copy of the last fitted parameters.

Returns:

copy of the last fitted parameters.

See Also:

fit()

osculatingValue

public double osculatingValue(AbsoluteDate date)

Get fitted osculating value.

Parameters:

date - current date

Returns:

osculating value at current date

osculatingDerivative

public double osculatingDerivative(AbsoluteDate date)

Get fitted osculating derivative.

Parameters:

date - current date

Returns:

osculating derivative at current date

osculatingSecondDerivative

public double osculatingSecondDerivative(AbsoluteDate date)

Get fitted osculating second derivative.

Parameters:

date - current date

Returns:

osculating second derivative at current date

meanValue

public double meanValue(AbsoluteDate date,
                        int degree,
                        int harmonics)

Get mean value, truncated to first components.

Parameters:

date - current date

degree - degree of polynomial secular part to consider

harmonics - number of harmonics terms to consider

Returns:

mean value at current date

meanDerivative

public double meanDerivative(AbsoluteDate date,
                             int degree,
                             int harmonics)

Get mean derivative, truncated to first components.

Parameters:

date - current date

degree - degree of polynomial secular part to consider

harmonics - number of harmonics terms to consider

Returns:

mean derivative at current date

approximateAsPolynomialOnly

public double[] approximateAsPolynomialOnly(int combinedDegree,
                                            AbsoluteDate combinedReference,
                                            int meanDegree,
                                            int meanHarmonics,
                                            AbsoluteDate start,
                                            AbsoluteDate end,
                                            double step)

Approximate an already fitted model to polynomial only terms.

This method is mainly used in order to combine the large amplitude long periods with the secular part as a new approximate polynomial model over some time range. This should be used rather than simply extracting the polynomial coefficients from getFittedParameters() when some periodic terms amplitudes are large (for example Sun resonance effects on local solar time in sun synchronous orbits). In theses cases, the pure polynomial secular part in the coefficients may be far from the mean model.

Parameters:

combinedDegree - desired degree for the combined polynomial

combinedReference - desired reference date for the combined polynomial

meanDegree - degree of polynomial secular part to consider

meanHarmonics - number of harmonics terms to consider

start - start date of the approximation time range

end - end date of the approximation time range

step - sampling step

Returns:

coefficients of the approximate polynomial (in increasing degree order), using the user provided reference date

meanSecondDerivative

public double meanSecondDerivative(AbsoluteDate date,
                                   int degree,
                                   int harmonics)

Get mean second derivative, truncated to first components.

Parameters:

date - current date

degree - degree of polynomial secular part

harmonics - number of harmonics terms to consider

Returns:

mean second derivative at current date