linprm Struct Reference

Linear transformation parameters. More...

#include <lin.h>

Data Fields
int	flag
int	naxis
double *	crpix
double *	pc
double *	cdelt
double *	piximg
double *	imgpix
int	unity
int	i_naxis
int	m_flag
int	m_naxis
double *	m_crpix
double *	m_pc
double *	m_cdelt

---

Detailed Description

The linprm struct contains all of the information required to perform a linear transformation. It consists of certain members that must be set by the user (given) and others that are set by the WCSLIB routines (returned).

---

Field Documentation

int linprm::flag

(Given and returned) This flag must be set to zero whenever any of the following members of the linprm struct are set or modified:

• linprm::naxis (q.v., not normally set by the user),
• linprm::pc,
• linprm::cdelt.

This signals the initialization routine, linset(), to recompute the returned members of the linprm struct. linset() will reset flag to indicate that this has been done.

PLEASE NOTE: flag should be set to -1 when linini() is called for the first time for a particular linprm struct in order to initialize memory management. It must ONLY be used on the first initialization otherwise memory leaks may result.

int linprm::naxis

(Given or returned) Number of pixel and world coordinate elements.

If linini() is used to initialize the linprm struct (as would normally be the case) then it will set naxis from the value passed to it as a function argument. The user should not subsequently modify it.

double * linprm::crpix

(Given) Pointer to the first element of an array of double containing the coordinate reference pixel, CRPIXja.

double * linprm::pc

(Given) Pointer to the first element of the PCi_ja (pixel coordinate) transformation matrix. The expected order is

        struct linprm lin;
        lin.pc = {PC1_1, PC1_2, PC2_1, PC2_2};

This may be constructed conveniently from a 2-D array via

        double m[2][2] = {{PC1_1, PC1_2},
                          {PC2_1, PC2_2}};

which is equivalent to

        double m[2][2];
        m[0][0] = PC1_1;
        m[0][1] = PC1_2;
        m[1][0] = PC2_1;
        m[1][1] = PC2_2;

The storage order for this 2-D array is the same as for the 1-D array, whence

        lin.pc = *m;

would be legitimate.

double * linprm::cdelt

(Given) Pointer to the first element of an array of double containing the coordinate increments, CDELTia.

double * linprm::piximg

(Returned) Pointer to the first element of the matrix containing the product of the CDELTia diagonal matrix and the PCi_ja matrix.

double * linprm::imgpix

(Returned) Pointer to the first element of the inverse of the linprm::piximg matrix.

int linprm::unity

(Returned) True if the linear transformation matrix is unity.

int linprm::i_naxis

(For internal use only.)

int linprm::m_flag

(For internal use only.)

int linprm::m_naxis

(For internal use only.)

double * linprm::m_crpix

(For internal use only.)

double * linprm::m_pc

(For internal use only.)

double * linprm::m_cdelt

(For internal use only.)

---