encapsulates beam squint (RR and LL beams at different directions) More...

#include <BeamSquint.h>

Public Types
enum	SquintType { NONE, RR, LL, GOFIGURE }
	Allowed Squints: NONE = no squint: PB is centered on the pointing center RR = PB is shifted from pointing center by amount in PBMathInterface's squint_p LL = PB is shifted from pointing center by the NEGATIVE of the amount in PBMathInterface's squint_p GOFIGURE = do the appropriate thing based on the STOKES of the Image. More...

Public Member Functions
	BeamSquint ()
	Default constructor initializes to zero. More...

	BeamSquint (const casacore::MDirection &squint, const casacore::Quantity &refFreq)
	Smart constructor to initialize the casacore::MDirection and reference freq. More...

	BeamSquint (const BeamSquint &other)
	Copy constructor. More...

BeamSquint &	operator= (const BeamSquint &other)
	Operator=. More...

	~BeamSquint ()
	Destructor. More...

void	show ()
	Show to Logger. More...

casacore::Bool	isNonNull ()
	Is BeamSquint nonNull? More...

casacore::MDirection &	scale (const casacore::Quantity &refFreq)
	Return the squint's casacore::MDirection scaled to a particular frequency. More...

void	getPointingDirection (const casacore::MDirection &pointDir, const casacore::Quantity parAngle, const casacore::Quantity obsFreq, const SquintType doSquint, casacore::MDirection &newPointingDir)
	Return the squinted pointing position. More...

Protected Attributes
casacore::MDirection	squint_p

casacore::Quantity	refFreq_p

Detailed Description

encapsulates beam squint (RR and LL beams at different directions)

Intended use:

Public interface

Prerequisite

casacore::MDirection class

Etymology

BeamSquint = Beam Squint. Obviously so.

Synopsis

Beam squint is when the RR and LL circular polarization beams are located in different places on the sky. The effect is due to the RR and LL feeds being off-axis. The VLA has particularly bad beam squint. Some instruments like the AT or WSRT have essentially no beam squint. The nominal pointing position is taken to be right in between the RR and LL beam centers/

BeamSquint has an casacore::MDirection which represents the angular offset from the nominal pointing position at Parallactic angle = 0 (ie, observing a source south of zenith at transit) and the actual RR beam. BeamSquint also has a reference frequency, and the magnitude of the squint angular offset is inversely proportional with frequency. The squint offset is a true angular displacement.

The main thing that BeamSquint does is: given the nominal pointing position and the parallactic angle, calculate the actual squinted beam position for the RR or LL beams. If BeamSquint::NONE is requested, the nominal pointing position is returned.

Example

casacore::MDirection oldPointing;
casacore::MDirection newPointing;
casacore::Quantity parallacticAngle(C::pi/2, "rad");
casacore::Quantity observingFreq(1.4142, "GHz");
BeamSquint oneBS(casacore::MDirection(casacore::Quantity(1.0, "'"), casacore::Quantity(1.0, "'"),
casacore::MDirection::Ref(casacore::MDirection::AZEL)),
casacore::Quantity(1.0, "GHz"));
oneBS.getPointingDirection(oldPointing, parallacticAngle,
observingFreq, BeamSquint::RR, newPointing);

Motivation

Boy, is this UGLY. We do that UGLY stuff just once, though, so you never have to look at it AGAIN (see getPointingDirection if you still don't believe me).

To Do

Hmmm?

Definition at line 101 of file BeamSquint.h.

Member Enumeration Documentation

enum casa::BeamSquint::SquintType

Allowed Squints: NONE = no squint: PB is centered on the pointing center RR = PB is shifted from pointing center by amount in PBMathInterface's squint_p LL = PB is shifted from pointing center by the NEGATIVE of the amount in PBMathInterface's squint_p GOFIGURE = do the appropriate thing based on the STOKES of the Image.

Enumerator
NONE
RR
LL
GOFIGURE

Definition at line 109 of file BeamSquint.h.

Constructor & Destructor Documentation

casa::BeamSquint::BeamSquint ( )

Default constructor initializes to zero.

casa::BeamSquint::BeamSquint	(	const casacore::MDirection &	squint,
		const casacore::Quantity &	refFreq
	)

Smart constructor to initialize the casacore::MDirection and reference freq.

casa::BeamSquint::BeamSquint ( const BeamSquint & other )

Copy constructor.

casa::BeamSquint::~BeamSquint ( )

Destructor.

Member Function Documentation

void casa::BeamSquint::getPointingDirection	(	const casacore::MDirection &	pointDir,
		const casacore::Quantity	parAngle,
		const casacore::Quantity	obsFreq,
		const SquintType	doSquint,
		casacore::MDirection &	newPointingDir
	)

Return the squinted pointing position.

casacore::Bool casa::BeamSquint::isNonNull ( )

Is BeamSquint nonNull?

BeamSquint& casa::BeamSquint::operator= ( const BeamSquint & other )

Operator=.

casacore::MDirection& casa::BeamSquint::scale ( const casacore::Quantity & refFreq )

Return the squint's casacore::MDirection scaled to a particular frequency.

void casa::BeamSquint::show ( )

Show to Logger.

Member Data Documentation

casacore::Quantity casa::BeamSquint::refFreq_p

protected

Definition at line 146 of file BeamSquint.h.

casacore::MDirection casa::BeamSquint::squint_p