Nutation.h

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 <aips/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

Member Description

enum NutationTypes

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

Nutation()

Default constructor, generates default J2000 Nutation identification

Nutation(const Nutation &other)

Copy constructor

explicit 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()
void init(NutationTypes type)

Re-initialise Nutation object

void refresh()

Refresh calculations

Double eqox(Double epoch)
Quantity getEqoxAngle(Double epoch)
Quantity getEqoxAngle(Double epoch, const Unit &unit)

Get the equation of equinox

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

void copy(const Nutation &other)

Make a copy

void fill()

Fill an empty copy

void calcNut(Double t)

Calculate Nutation angles for time t