fr.cnes.sirius.patrius.frames.configuration.precessionnutation

Class PrecessionNutationInterpolation

java.lang.Object

fr.cnes.sirius.patrius.frames.configuration.precessionnutation.PrecessionNutationInterpolation

All Implemented Interfaces:

PrecessionNutationModel, Serializable

public class PrecessionNutationInterpolation
extends Object
implements PrecessionNutationModel

Precession nutation correction computation through an interpolation process.

This implementation includes a caching/interpolation feature to tremendously improve efficiency. The IAU-2000 model involves lots of terms (1600 components for x, 1275 components for y and 66 components for s). Recomputing all these components for each point is really slow. The shortest period for these components is about 5.5 days (one fifth of the moon revolution period), hence the pole motion is smooth at the day or week scale. This implies that these motions can be computed accurately using a few reference points per day or week and interpolated between these points. This implementation uses 4 points (CIP and CIP velocities) separated by 1/2 day (43200 seconds) each, the resulting maximal interpolation error on the frame is about 1.3×10^-10 arcseconds.

Some information about performance: The CIP coordinates are interpolated thanks to reference CIPCoordinates that we will call "references".
These references are computed in function of the needs for the interpolation. For implementation simplicity, it is imposed that there is no holes between references. Thus, if dates are too apart from each other (more than allowedExtensionBeforeEphemerisReset holes to be filled), the references are reinitialized. As a consequence, if the dates are erratically spread, it is advised to pre-initialize the reference values with #initializeCipEphemeris in order to avoid too many re-initializations of the references.
Another aspect is that if the required dates are separated of more than the getInterpolationStep(), the interpolation management will not be efficient and it is advised to use a direct PrecessionNutationModel instead.

Since:

4.13

Author:

veuillh

See Also:

Serialized Form

Field Summary

Fields

Modifier and Type	Field and Description
static int	DEFAULT_ALLOWED_EXTENSION_BEFORE_EPHEM_RESET Default allowed extra CIPCoordinates to compute in order to keep the same ephemeris.
static int	DEFAULT_EPHEM_MAX_SIZE Default ephemeris max size before resetting for memory usage purpose.
static int	DEFAULT_INTERP_ORDER Default number of interpolation points.
static int	DEFAULT_INTERP_STEP Default time span between generated reference points.

Constructor Summary

Constructors

Constructor and Description
PrecessionNutationInterpolation(PrecessionNutationModel pnModel) Simple constructor with default values.
PrecessionNutationInterpolation(PrecessionNutationModel pnModel, int interpolationStep, int interpolationOrder, int ephemerisMaxSize, int allowedExtensionBeforeEphemerisReset) Main constructor.

Method Summary

Modifier and Type	Method and Description
int	getAllowedExtensionBeforeEphemerisReset() Getter for the maximum allowed reference extensions before reinitialization.
CIPCoordinates	getCIPCoordinates(AbsoluteDate date) Getter for the CIP coordinates at the provided date.
AbsoluteDateInterval	getCurrentUsableInterval() Getter for the current usable interval of the ephemeris.
double	getEphemerisCacheReusabilityRatio() Getter for the cache reusability ratio.
int	getEphemerisMaxSize() Getter for the maximal internal reference values size before reinitialization.
int	getEphemerisSize() Getter for the ephemeris size.
int	getInterpolationOrder() Getter for the interpolation order.
int	getInterpolationStep() Getter for the interpolation step.
PrecessionNutationModel	getModel() Getter for the internal precession nutation model.
FrameConvention	getOrigin() Get IERS model origin.
void	initializeCIPEphemeris(AbsoluteDate firstUsableDate, AbsoluteDate lastUsableDate) Pre-initialize (optional) the CIP coordinates for a given interval for performance purpose.
boolean	isDirect() Return computation type : direct or interpolated.

Methods inherited from class java.lang.Object

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

Field Detail

DEFAULT_INTERP_ORDER

public static final int DEFAULT_INTERP_ORDER

Default number of interpolation points.

See Also:

Constant Field Values

DEFAULT_INTERP_STEP

public static final int DEFAULT_INTERP_STEP

Default time span between generated reference points.

See Also:

Constant Field Values

DEFAULT_EPHEM_MAX_SIZE

public static final int DEFAULT_EPHEM_MAX_SIZE

Default ephemeris max size before resetting for memory usage purpose.

See Also:

Constant Field Values

DEFAULT_ALLOWED_EXTENSION_BEFORE_EPHEM_RESET

public static final int DEFAULT_ALLOWED_EXTENSION_BEFORE_EPHEM_RESET

Default allowed extra CIPCoordinates to compute in order to keep the same ephemeris.

See Also:

Constant Field Values

Constructor Detail

PrecessionNutationInterpolation

public PrecessionNutationInterpolation(PrecessionNutationModel pnModel)

Simple constructor with default values.

Parameters:

pnModel - Precession nutation model to use (must be a direct).

Throws:

IllegalArgumentException - if the precession nutation model is not direct

PrecessionNutationInterpolation

public PrecessionNutationInterpolation(PrecessionNutationModel pnModel,
                                       int interpolationStep,
                                       int interpolationOrder,
                                       int ephemerisMaxSize,
                                       int allowedExtensionBeforeEphemerisReset)

Main constructor.

Parameters:

pnModel - Precession nutation model to use (must be a direct).

interpolationStep - time span between interpolation points

interpolationOrder - number of interpolation points to use

ephemerisMaxSize - Max size of the internal ephemeris before reset (too avoid memory leaks)

allowedExtensionBeforeEphemerisReset - When a new CIP coordinates needs to be interpolated while not present in the ephemeris, the latter is extended. This parameter corresponds to the maximum number of CIPCoordinates allowed for the extension before resetting the ephemeris around the required date.

Throws:

IllegalArgumentException - if the number of interpolation points is < 2
if the number of interpolation points is not even
if the precession nutation model is not direct

Method Detail

initializeCIPEphemeris

public void initializeCIPEphemeris(AbsoluteDate firstUsableDate,
                                   AbsoluteDate lastUsableDate)

Pre-initialize (optional) the CIP coordinates for a given interval for performance purpose.

Can be useful when CIP coordinates are required at very different dates that would lead to multiple ephemeris re-initializations (with regards to the allowedExtensionBeforeEphemerisReset.
Calling this method does not prevent the class to extend the ephemeris, it is just a way to reduce the re-initialization occurrences.

This method is thread-safe.

Parameters:

firstUsableDate - First usable date of the ephemeris

lastUsableDate - Last usable date of the ephemeris

Throws:

IllegalArgumentException - if the ephemeris exceeds the maximum allowed size

getCIPCoordinates

public CIPCoordinates getCIPCoordinates(AbsoluteDate date)

Getter for the CIP coordinates at the provided date.

This method is thread-safe.

Specified by:

getCIPCoordinates in interface PrecessionNutationModel

Parameters:

date - Date for the CIP coordinates

Returns:

the CIP coordinates

getInterpolationOrder

public int getInterpolationOrder()

Getter for the interpolation order.

Returns:

the interpolation order

getInterpolationStep

public int getInterpolationStep()

Getter for the interpolation step.

Returns:

the interpolation step

getEphemerisMaxSize

public int getEphemerisMaxSize()

Getter for the maximal internal reference values size before reinitialization.

Returns:

the maximal internal reference values size before reinitialization

getAllowedExtensionBeforeEphemerisReset

public int getAllowedExtensionBeforeEphemerisReset()

Getter for the maximum allowed reference extensions before reinitialization.

Returns:

the maximum allowed reference extensions before reinitialization

getModel

public PrecessionNutationModel getModel()

Getter for the internal precession nutation model.

Returns:

the internal precession nutation model

getCurrentUsableInterval

public AbsoluteDateInterval getCurrentUsableInterval()

Getter for the current usable interval of the ephemeris.

Returns:

the current usable interval of the ephemeris. Can be null if the ephemeris has not been initialized yet.

getEphemerisCacheReusabilityRatio

public double getEphemerisCacheReusabilityRatio()

Getter for the cache reusability ratio.
See TimeStampedInterpolableEphemeris.getCacheReusabilityRatio() for more information.

Returns:

the reusability ratio

getEphemerisSize

public int getEphemerisSize()

Getter for the ephemeris size.

Returns:

the ephemeris size

isDirect

public boolean isDirect()

Return computation type : direct or interpolated.

Specified by:

isDirect in interface PrecessionNutationModel

Returns:

true if direct computation, false if interpolated

getOrigin

public FrameConvention getOrigin()

Get IERS model origin.

Specified by:

getOrigin in interface PrecessionNutationModel

Returns:

IERS model origin