EarthField class model calculations. More...

#include <EarthField.h>

Public Types
enum	EarthFieldTypes { IGRF, NONE, STANDARD }
	Known EarthField calculation models. More...
Public Member Functions
	EarthField ()
	Default constructor, generates default J2000 EarthField identification.
	EarthField (const EarthField &other)
	Copy constructor.
	EarthField (EarthFieldTypes model, Double catepoch=51544.5)
	Constructor with epoch in MJulian days (default is J2000)
EarthField &	operator= (const EarthField &other)
	Copy assignment.
	~EarthField ()
const Vector< Double > &	operator() (const MVPosition &pos)
	Return the EarthField components.
const Vector< Double > *	derivative (const MVPosition &pos)
	Return derivatives of field (to X, Y, Z).
void	init ()
	Re-initialise EarthField object with specified model and epoch, or defaults STANDARD and J2000.
void	init (EarthFieldTypes model, Double catepoch=51544.5)
void	refresh ()
	Refresh calculations.
Static Public Attributes
static const Double	INTV
	Default interval to be used for linear approximation (in m)
Private Member Functions
void	copy (const EarthField &other)
	Make a copy.
void	fillField ()
	Create correct default fixedEpoch and catalogue field data.
void	calcField (const MVPosition &pos)
	Calculate EarthField for longitude and latitude and altitude (m)
Private Attributes
EarthFieldTypes	method_p
	Method to be used.
Double	fixedEpoch_p
	Fixed epoch to be used (MJD)
Vector< Double >	agh_p
	List of spherical components.
Vector< Double >	p_p
	Work arrays for calculations.
Vector< Double >	q_p
Vector< Double >	cl_p
Vector< Double >	sl_p
MVPosition	checkPos_p
	Check position.
Double	pval_p [3]
	Cached calculated field components.
Double	dval_p [3][3]
	Cached derivatives.
Int	lres_p
	To reference results, and use a few in interim calculations, results are calculated in a circular buffer.
Vector< Double >	result_p [4]
	Last calculation.
Static Private Attributes
static uInt	interval_reg_p
	Interpolation interval.

Detailed Description

EarthField class model calculations.

Intended use:

Internal

 <h3>Review Status</h3><dl><dt>Reviewed By:<dd>UNKNOWN<dt>Date Reviewed:<dd>before2004/08/25<dt>Test programs:<dd>tEarthField</dl>

Prerequisite

Measure class for use
MeasTable class for data

Etymology

Earth magnetic Field model

Synopsis

EarthField forms the class for Earth magnetic field calculations. It is a simple container with the selected model, and the mean epoch.
The method is selected from one of the following:

EarthField::STANDARD (at 1998/05/18 the IGRF definition)
EarthField::IGRF (IGRF reference field model)

Epochs can be specified as the MJD (with defined constants MeasData::MJD2000 and MeasData::MJD1950 or the actual MJD), leading to the following constructors:

EarthField() default; assuming IGRF and MJD2000
EarthField(method); assuming J2000 as epoch
EarthField(method, epoch) with epoch Double(MJD)

Actual EarthField for a certain position on Earth is calculated by the () operator. Arguments can be:

MVPosition: a position on Earth (in the ITRF frame)

The returned value is a 3D vector of the field (in nT) in ITRF coordinates. The derivative (d^-1) can be obtained as well by derivative(MVPosition).
An EarthField can be re-initialised with a different method and/or other epoch with the init() functions (same format as constructors).

To bypass the full, lengthy calculation actual returned values are calculated using the derivative if within about 50 km (error less than about 10^-2 G). A call to refresh() will re-initiate calculations from scratch.
The following details can be set with the Aipsrc mechanism:

measures.earthfield.d_interval: approximation radius (km is default unit) over which a linear approximation is used

The field model is assumed to be constant over the time-span the class is used.

The calculations are based on a routine provided by the IGRF community. See ftp.ngdc.noaa.gov/Solid_Earth/Mainfld_Mag/Models/IAGA, routine IGRFLIB.FOR. The values are in nT (10uG).

Example

        EarthField mine(EarthField::STANDARD,
                         45837.0);              // define EarthField type
                                                // for 84/05/17
        MPosition pos;
         MeasTable::Observatory(pos, "WSRT");   // Obervatory position
     // Make sure correct position frame used
         MVPosition x(MPosition::Convert(pos, MPosition::ITRF)().getValue());
        MVEarthMagnetic now = mine(x);          // get EarthField

Motivation

To have a container (with history) for field calculations

To Do

nothing I know off

Definition at line 130 of file EarthField.h.

Member Enumeration Documentation

enum casa::EarthField::EarthFieldTypes

Known EarthField calculation models.

Enumerator:

IGRF	Standard IGRF model.
NONE	Make the field equal to zero.
STANDARD	Standard default model if none specified.

Definition at line 140 of file EarthField.h.

Constructor & Destructor Documentation

casa::EarthField::EarthField ( )

Default constructor, generates default J2000 EarthField identification.

casa::EarthField::EarthField ( const EarthField & other )

Copy constructor.

casa::EarthField::EarthField	(	EarthFieldTypes	model,
		Double	catepoch = `51544.5`
	)		`[explicit]`

Constructor with epoch in MJulian days (default is J2000)

casa::EarthField::~EarthField ( )

Member Function Documentation

void casa::EarthField::calcField ( const MVPosition & pos ) [private]

Calculate EarthField for longitude and latitude and altitude (m)

void casa::EarthField::copy ( const EarthField & other ) [private]

Make a copy.

const Vector<Double>* casa::EarthField::derivative ( const MVPosition & pos )

Return derivatives of field (to X, Y, Z).

Note that the value returned has only a lifetime as long as the EarthField container exists, and no new components or derivative is calculated. The returned value should not be deleted.

void casa::EarthField::fillField ( ) [private]

Create correct default fixedEpoch and catalogue field data.

void casa::EarthField::init ( )

Re-initialise EarthField object with specified model and epoch, or defaults STANDARD and J2000.