LinearXform.h

Classes

LinearXform -- Perform a linear transform between input and output vectors (full description)

class LinearXform

Interface

Public Members
LinearXform(uInt naxis=1)
LinearXform(const Vector<Double> &crpix, const Vector<Double> &cdelt)
LinearXform(const Vector<Double> &crpix, const Vector<Double> &cdelt, const Matrix<Double> &pc)
LinearXform(const LinearXform &other)
LinearXform &operator=(const LinearXform &other)
~LinearXform()
uInt nWorldAxes() const
Bool forward(Vector<Double> &pixel, const Vector<Double> &world, String &errorMsg) const
Bool reverse(Vector<Double> &world, const Vector<Double> &pixel, String &errorMsg) const
Vector<Double> crpix() const
Vector<Double> cdelt() const
Matrix<Double> pc() const
void crpix(const Vector<Double> &newvals)
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
Bool near(const LinearXform& other, Double tol=1e-6) const
Bool near(const LinearXform& other, const Vector<Int>& excludeAxes, Double tol=1e-6) const
Private Members
void set_linprm()

Description

Review Status

Reviewed By:
Peter Barnes
Date Reviewed:
1999/12/24
Programs:
Tests:

Prerequisite

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

To Do

Member Description

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.

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.

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.

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
Bool reverse(Vector<Double> &world, const Vector<Double> &pixel, 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.

Vector<Double> crpix() const
Vector<Double> cdelt() const
Matrix<Double> pc() const

Retrieve the value of crpix, cdelt, and pc.

void crpix(const Vector<Double> &newvals)
void cdelt(const Vector<Double> &newvals)
void pc(const Matrix<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);

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

void set_linprm()