casacore::Nutation Class Reference

Nutation class and calculations. More...

#include <Nutation.h>

Public Types
enum	NutationTypes { NONE, IAU1980, B1950, IAU2000A, IAU2000B, IAU2000, STANDARD }
	Types of known Nutation calculations (at 1995/09/04 STANDARD == IAU1980, after 2004/01/01 it will be IAU2000B)). More...
Public Member Functions
	Nutation ()
	Default constructor, generates default J2000 Nutation identification.
	Nutation (const Nutation &other)
	Copy constructor.
	Nutation (NutationTypes type)
	Constructor with type.
Nutation &	operator= (const Nutation &other)
	Copy assignment.
	~Nutation ()
const Euler &	operator() (Double epoch)
	Return the Nutation angles.
const Euler &	derivative (Double epoch)
	Return derivative of Nutation (d^-1).
void	init ()
	Re-initialise Nutation object.
void	init (NutationTypes type)
void	refresh ()
	Refresh calculations.
Double	eqox (Double epoch)
	Get the equation of equinox.
Quantity	getEqoxAngle (Double epoch)
Quantity	getEqoxAngle (Double epoch, const Unit &unit)
Double	derivativeEqox (Double epoch)
	Get the derivative of the equation of equinoxes in d^-1.
Double	eqoxCT (Double epoch)
	Get the complimentary terms of the equation of equinoxes.
Double	derivativeEqoxCT (Double epoch)
	Get the derivative of the complimentary terms of the equation of equinoxes.
Static Public Attributes
static const Double	INTV
	Interval to be used for linear approximation (in days).
Private Member Functions
void	copy (const Nutation &other)
	Make a copy.
void	fill ()
	Fill an empty copy.
void	calcNut (Double t, Bool calcDer=False)
	Calculate Nutation angles for time t; also derivatives if True given.
Private Attributes
NutationTypes	method_p
	Method to be used.
Double	checkEpoch_p
	Check epoch for linear approximation.
Double	checkDerEpoch_p
	Check epoch for calculation of derivatives.
Double	nval_p [3]
	Cached calculated angles.
Double	dval_p [3]
	Cached derivatives.
Double	eqeq_p
	Cached equation of equinoxes.
Double	deqeq_p
	Cached derivative equation of equinoxes.
Double	neval_p
	Cached complimentary terms equation of equinoxes.
Double	deval_p
	Cached derivative of complimentary terms equation of equinoxes.
Int	lres_p
	To be able to use references rather than copies, and also to use these references in simple (up to 4 terms of Nutation results) expressions, results are calculated in circulating buffer.
Euler	result_p [4]
	Last calculation.
Static Private Attributes
static uInt	myInterval_reg
	Interpolation interval.
static uInt	myUseiers_reg
	IERS use.
static uInt	myUsejpl_reg
	JPL use.

Detailed Description

Nutation class and calculations.

Intended use:

Public interface

Review Status

Reviewed By:: Tim Cornwell
Date Reviewed:: 1996/07/01
Test programs:: tMeasMath

Prerequisite

Measure class
Euler
MeasData class for constants

Etymology

Nutation

Synopsis

Nutation forms the class for Nutation calculations. It is a simple container with the selected method, and the mean epoch. It acts as a cache for values and their derivatives, to enable fast calculations for time epochs close together (see the aipsrc variable measures.nutation.d_interval).

The calculation method is selected from one of the following:

Nutation::STANDARD (at 1995/09/04 the IAU1980 definition, from 2004/01/01 IAU2000B)
Nutation::NONE (nutation of zero returned)
Nutation::IAU1980
Nutation::B1950
Nutation::IAU2000
Nutation::IAU2000A (equal to the full precision (uas) IAU2000)
Nutation::IAU2000B (official lower precision (mas) of IAU2000)

Epochs can be specified as the MJD (with defined constants MeasData::MJD2000 and MeasData::MJDB1950 or the actual MJD), leading to the following constructors:

Nutation() default; assuming STANDARD
Nutation(method)

Actual Nutation for a certain Epoch is calculated by the () operator as Nutation(epoch), with epoch Double MJD. Values are returned as an Euler . The derivative (d^-1) can be obtained as well by derivative(epoch).
A Nutation can be re-initialed with a different method and/or zero epoch with the init() functions (same format as constructors). To bypass the full calculation actual returned values are calculated using the derivative if within about 2 hours (error less than about 10^-5 mas). A call to refresh() will re-initiate calculations from scratch.
The following details can be set with the Aipsrc mechanism:

measures.nutation.d_interval: approximation interval as time (fraction of days is default unit) over which linear approximation is used (default 0.04d (about 1 hour)).
measures.nutation.b_usejpl: use the JPL database nutations for IAU1980. Else analytical expression, relative error about 10^-9 Note that the JPL database to be used can be set with measures.jpl.ephemeris (at the moment of writing DE200 (default), or DE405)
measures.nutation.b_useiers: use the IERS Database nutation corrections for IAU1980 (default False)

Example

 #include <casacore/measures/Measures.h>
 MVDirection pos(Quantity(10,"degree"),Quantity(-10.5,"degree"));
 // direction RA=10; DEC=-10.5
 Nutation mine(Nutation::IAU1980);      // define nutation type
 RotMatrix rotat(mine(45837.0));                // rotation matrix for 84/05/17
 MVDirection new = rotat*pos;           // apply nutation

The normal way to use Nutation is by using the MeasConvert class.

Motivation

To calculate the Nutation angles. An alternate route could have been a global function, but having a simple container allows caching of some calculations for speed.
Using MJD (JD-2400000.5) rather than JD is for precision reasons.

To Do

Correct deval_p (derivative complimentary eqox terms)
Improve speed by a bit more lazyness in derivative calculations and separate eqox calculations

Definition at line 139 of file Nutation.h.

Member Enumeration Documentation

enum casacore::Nutation::NutationTypes

Types of known Nutation calculations (at 1995/09/04 STANDARD == IAU1980, after 2004/01/01 it will be IAU2000B)).

Enumerator:

NONE
IAU1980
B1950
IAU2000A
IAU2000B
IAU2000
STANDARD

Definition at line 148 of file Nutation.h.

Constructor & Destructor Documentation

casacore::Nutation::Nutation ( )

Default constructor, generates default J2000 Nutation identification.

casacore::Nutation::Nutation ( const Nutation & other )

Copy constructor.

casacore::Nutation::Nutation ( NutationTypes type ) [explicit]

Constructor with type.

casacore::Nutation::~Nutation ( )

Member Function Documentation

void casacore::Nutation::calcNut	(	Double	t,
		Bool	calcDer = `False`
	)			`[private]`

Calculate Nutation angles for time t; also derivatives if True given.

void casacore::Nutation::copy ( const Nutation & other ) [private]

Make a copy.

const Euler& casacore::Nutation::derivative ( Double epoch )

Return derivative of Nutation (d^-1).

Double casacore::Nutation::derivativeEqox ( Double epoch )

Get the derivative of the equation of equinoxes in d^-1.

Double casacore::Nutation::derivativeEqoxCT ( Double epoch )

Get the derivative of the complimentary terms of the equation of equinoxes.

Double casacore::Nutation::eqox ( Double epoch )

Get the equation of equinox.

Double casacore::Nutation::eqoxCT ( Double epoch )

Get the complimentary terms of the equation of equinoxes.

void casacore::Nutation::fill ( ) [private]

Fill an empty copy.

Quantity casacore::Nutation::getEqoxAngle	(	Double	epoch,
		const Unit &	unit
	)

Quantity casacore::Nutation::getEqoxAngle ( Double epoch )

void casacore::Nutation::init ( NutationTypes type )

void casacore::Nutation::init ( )

Re-initialise Nutation object.

const Euler& casacore::Nutation::operator() ( Double epoch )

Return the Nutation angles.

Nutation& casacore::Nutation::operator= ( const Nutation & other )

Copy assignment.

void casacore::Nutation::refresh ( )

Refresh calculations.

Member Data Documentation

Double casacore::Nutation::checkDerEpoch_p [private]

Check epoch for calculation of derivatives.

Definition at line 204 of file Nutation.h.

Double casacore::Nutation::checkEpoch_p [private]

Check epoch for linear approximation.

Definition at line 202 of file Nutation.h.

Double casacore::Nutation::deqeq_p [private]

Cached derivative equation of equinoxes.

Definition at line 212 of file Nutation.h.

Double casacore::Nutation::deval_p [private]

Cached derivative of complimentary terms equation of equinoxes.

Definition at line 216 of file Nutation.h.

Double casacore::Nutation::dval_p[3] [private]

Cached derivatives.

Definition at line 208 of file Nutation.h.

Double casacore::Nutation::eqeq_p [private]

Cached equation of equinoxes.

Definition at line 210 of file Nutation.h.

const Double casacore::Nutation::INTV [static]

Interval to be used for linear approximation (in days).

Definition at line 143 of file Nutation.h.

Int casacore::Nutation::lres_p [private]

To be able to use references rather than copies, and also to use these references in simple (up to 4 terms of Nutation results) expressions, results are calculated in circulating buffer.

Definition at line 220 of file Nutation.h.

NutationTypes casacore::Nutation::method_p [private]

Method to be used.

Definition at line 200 of file Nutation.h.

uInt casacore::Nutation::myInterval_reg [static, private]

Interpolation interval.

Definition at line 224 of file Nutation.h.

uInt casacore::Nutation::myUseiers_reg [static, private]

IERS use.

Definition at line 226 of file Nutation.h.

uInt casacore::Nutation::myUsejpl_reg [static, private]

JPL use.