Perform a linear transform between input and output vectors. More...

#include <LinearXform.h>

Public Member Functions
	LinearXform (uInt naxis=1)
	Construct with specified number of axes.
	LinearXform (const Vector< Double > &crpix, const Vector< Double > &cdelt)
	Construct the linear transformation from the supplied reference pixel and increment.
	LinearXform (const Vector< Double > &crpix, const Vector< Double > &cdelt, const Matrix< Double > &pc)
	Construct a linear transformation, supplying all of the reference pixel, increment and PC matrix.
	LinearXform (const LinearXform &other)
	Copy constructor (copy sematics)
LinearXform &	operator= (const LinearXform &other)
	Assignment (copy sematics)
	~LinearXform ()
	Destructor.
uInt	nWorldAxes () const
	Returns the number of world axes, which for this class is also the number of pixel axes.
Bool	forward (Vector< Double > &pixel, const Vector< Double > &world, String &errorMsg) const
	Convert world coordinates to pixel coordinates (forward), or pixel coordinates to world (reverse).
Bool	reverse (Vector< Double > &world, const Vector< Double > &pixel, String &errorMsg) const
Vector< Double >	crpix () const
	Retrieve the value of crpix, cdelt, and pc.
Vector< Double >	cdelt () const
Matrix< Double >	pc () const
void	crpix (const Vector< Double > &newvals)
	Set the value of crpix, cdelt, and pc.
void	cdelt (const Vector< Double > &newvals)
void	pc (const Matrix< Double > &newvals)
LinearXform *	fourierInvert (String &errMsg, const Vector< Bool > &axes, const Vector< Double > &crpix, const Vector< Double > &scale) const
	Invert the LinearXform ready for use in a Fourier Transformed Coordinate.
Bool	near (const LinearXform &other, Double tol=1e-6) const
	Comparison function.
Bool	near (const LinearXform &other, const Vector< Int > &excludeAxes, Double tol=1e-6) const
Private Member Functions
void	set_linprm ()
Private Attributes
linprm	linprm_p

Bool	isPCDiagonal_p

Detailed Description

Perform a linear transform between input and output vectors.

Intended use:

Internal

Review Status

Reviewed By:: Peter Barnes
Date Reviewed:: 1999/12/24
Test programs:: tLinearXform

Prerequisite

General knowledge of AIPS++ Arrays
Knowledge of FITS terminology in coordinate transformations

Synopsis

This class represents the common linear part of a FITS coordinate transformation. In particular it does the following:

    world = cdelt * PC * (pixel - crpix)

Where PC is an NxN matrix; pixel, crpix (reference pixel) and world are length N vectors; and cdelt (increment) is an NxN diagonal matrix, represented as a length N vector.

Normally this class isn't used directly, rather it is used indirectly through a class like LinearCoordinate .

The actual computations are performed by WCSLIB, written by Mark Calabretta of the ATNF.

Example

Let's make a LinearXform housing two axes with a unit diagonal PC matrix and convert from pixel to world

       Vector<Double> crpix(2), cdelt(2);
       crpix(0) = 10.0; crpix(1) = 20.0;
       cdelt(0) = 1.0; cdelt(1) = -1.0;
       LinearXform lxf(crpix, cdelt);
   
       String errMsg;
       Vector<Double> world, pixel(2);
       pixel = 10.0;
       Bool ok = lxf.reverse(world, pixel, errMsg);
       if (ok) {
          cerr << "pixel, world = " << pixel << world << endl;
       } else {
          cerr << "Error : " << errMsg << endl;
       }

The answer should be a world vector with values 0 and -10.

Motivation

Factor out the common linear part of coordinate transformations.

Thrown Exceptions

AipsError

To Do

Allow different numbers of pixel and world axes.

Definition at line 109 of file LinearXform.h.

Constructor & Destructor Documentation

casa::LinearXform::LinearXform ( uInt naxis = 1 )

Construct with specified number of axes.

The reference pixel is assumed to be 0, and the increment is assumed to be unity, and the PC matrix is assumed to be diagonal.

casa::LinearXform::LinearXform	(	const Vector< Double > &	crpix,
		const Vector< Double > &	cdelt
	)

Construct the linear transformation from the supplied reference pixel and increment.

The PC matrix is the unit matrix. crpix and cdelt must have the same number of elements.

casa::LinearXform::LinearXform	(	const Vector< Double > &	crpix,
		const Vector< Double > &	cdelt,
		const Matrix< Double > &	pc
	)

Construct a linear transformation, supplying all of the reference pixel, increment and PC matrix.

The vectors must be of the same length ("n") and the number of rows and columns in the matrix must also be n.

casa::LinearXform::LinearXform ( const LinearXform & other )

Copy constructor (copy sematics)

casa::LinearXform::~LinearXform ( )

Destructor.

Member Function Documentation

Vector<Double> casa::LinearXform::cdelt ( ) const

void casa::LinearXform::cdelt ( const Vector< Double > & newvals )

Vector<Double> casa::LinearXform::crpix ( ) const

Retrieve the value of crpix, cdelt, and pc.

void casa::LinearXform::crpix ( const Vector< Double > & newvals )

Set the value of crpix, cdelt, and pc.

Note that since you can only set one of them, you cannot change the dimensionality of the transform using these functions. Instead use assignment on a temporary, i.e.: linxform = LinearXform (crpix,crval,pc);

Bool casa::LinearXform::forward	(	Vector< Double > &	pixel,
		const Vector< Double > &	world,
		String &	errorMsg
	)		const

Convert world coordinates to pixel coordinates (forward), or pixel coordinates to world (reverse).

If the conversion works True is returned, otherwise False is returned and errorMsg is set. The output vectors are resized appropriately.

LinearXform* casa::LinearXform::fourierInvert	(	String &	errMsg,
		const Vector< Bool > &	axes,
		const Vector< Double > &	crpix,
		const Vector< Double > &	scale
	)		const

Invert the LinearXform ready for use in a Fourier Transformed Coordinate.

It is the callers responsibility to delete the pointer. If it fails the pointer is 0 and an error message is provided

Bool casa::LinearXform::near	(	const LinearXform &	other,
		Double	tol = `1e-6`
	)		const

Comparison function.

Any private Double data members are compared with the specified fractional tolerance. You can specify axes to exclude from the comparison if you wish.

Bool casa::LinearXform::near	(	const LinearXform &	other,
		const Vector< Int > &	excludeAxes,
		Double	tol = `1e-6`
	)		const

uInt casa::LinearXform::nWorldAxes ( ) const

Returns the number of world axes, which for this class is also the number of pixel axes.

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

Assignment (copy sematics)

Matrix<Double> casa::LinearXform::pc ( ) const

void casa::LinearXform::pc ( const Matrix< Double > & newvals )

Bool casa::LinearXform::reverse	(	Vector< Double > &	world,
		const Vector< Double > &	pixel,
		String &	errorMsg
	)		const

void casa::LinearXform::set_linprm ( ) [private]

Member Data Documentation

Bool casa::LinearXform::isPCDiagonal_p [private]

Definition at line 193 of file LinearXform.h.

linprm casa::LinearXform::linprm_p [mutable, private]

A WCSLIB C-structure.

Definition at line 191 of file LinearXform.h.

The documentation for this class was generated from the following file:

casacore/coordinates/Coordinates/LinearXform.h

Public Member Functions

Private Member Functions

Private Attributes