wcs.h File Reference

#include "lin.h"
#include "cel.h"
#include "spc.h"
#include "tab.h"
#include "wcserr.h"

Go to the source code of this file.

Data Structures

struct pvcard

Store for PVi_ma keyrecords. More...

struct pscard

Store for PSi_ma keyrecords. More...

struct wtbarr

Extraction of coordinate lookup tables from BINTABLE. More...

struct wcsprm

Coordinate transformation parameters. More...

Defines

#define WCSSUB_LONGITUDE   0x1001

Mask for extraction of longitude axis by wcssub().

#define WCSSUB_LATITUDE   0x1002

Mask for extraction of latitude axis by wcssub().

#define WCSSUB_CUBEFACE   0x1004

Mask for extraction of CUBEFACE axis by wcssub().

#define WCSSUB_CELESTIAL   0x1007

Mask for extraction of celestial axes by wcssub().

#define WCSSUB_SPECTRAL   0x1008

Mask for extraction of spectral axis by wcssub().

#define WCSSUB_STOKES   0x1010

Mask for extraction of STOKES axis by wcssub().

#define WCSLEN   (sizeof(struct wcsprm)/sizeof(int))

Size of the wcsprm struct in int units.

#define wcscopy(alloc, wcssrc, wcsdst)   wcssub(alloc, wcssrc, 0x0, 0x0, wcsdst)

Copy routine for the wcsprm struct.

#define wcsini_errmsg   wcs_errmsg

Deprecated.

#define wcssub_errmsg   wcs_errmsg

Deprecated.

#define wcscopy_errmsg   wcs_errmsg

Deprecated.

#define wcsfree_errmsg   wcs_errmsg

Deprecated.

#define wcsprt_errmsg   wcs_errmsg

Deprecated.

#define wcsset_errmsg   wcs_errmsg

Deprecated.

#define wcsp2s_errmsg   wcs_errmsg

Deprecated.

#define wcss2p_errmsg   wcs_errmsg

Deprecated.

#define wcsmix_errmsg   wcs_errmsg

Deprecated.

Enumerations

enum wcs_errmsg_enum {
  WCSERR_SUCCESS = 0, WCSERR_NULL_POINTER = 1, WCSERR_MEMORY = 2, WCSERR_SINGULAR_MTX = 3,
  WCSERR_BAD_CTYPE = 4, WCSERR_BAD_PARAM = 5, WCSERR_BAD_COORD_TRANS = 6, WCSERR_ILL_COORD_TRANS = 7,
  WCSERR_BAD_PIX = 8, WCSERR_BAD_WORLD = 9, WCSERR_BAD_WORLD_COORD = 10, WCSERR_NO_SOLUTION = 11,
  WCSERR_BAD_SUBIMAGE = 12, WCSERR_NON_SEPARABLE = 13
}

Functions

int wcsnpv (int n)

Memory allocation for PVi_ma.

int wcsnps (int n)

Memory allocation for PSi_ma.

int wcsini (int alloc, int naxis, struct wcsprm *wcs)

Default constructor for the wcsprm struct.

int wcssub (int alloc, const struct wcsprm *wcssrc, int *nsub, int axes[], struct wcsprm *wcsdst)

Subimage extraction routine for the wcsprm struct.

int wcsfree (struct wcsprm *wcs)

Destructor for the wcsprm struct.

int wcsprt (const struct wcsprm *wcs)

Print routine for the wcsprm struct.

int wcsperr (const struct wcsprm *wcs, const char *prefix)

Print error messages from a wcsprm struct.

int wcsset (struct wcsprm *wcs)

Setup routine for the wcsprm struct.

int wcsp2s (struct wcsprm *wcs, int ncoord, int nelem, const double pixcrd[], double imgcrd[], double phi[], double theta[], double world[], int stat[])

Pixel-to-world transformation.

int wcss2p (struct wcsprm *wcs, int ncoord, int nelem, const double world[], double phi[], double theta[], double imgcrd[], double pixcrd[], int stat[])

World-to-pixel transformation.

int wcsmix (struct wcsprm *wcs, int mixpix, int mixcel, const double vspan[], double vstep, int viter, double world[], double phi[], double theta[], double imgcrd[], double pixcrd[])

Hybrid coordinate transformation.

int wcssptr (struct wcsprm *wcs, int *i, char ctype[9])

Spectral axis translation.

Variables

const char * wcs_errmsg []

Status return messages.

Detailed Description

These routines implement the FITS World Coordinate System (WCS) standard which defines methods to be used for computing world coordinates from image pixel coordinates, and vice versa. They are based on the wcsprm struct which contains all information needed for the computations. The struct contains some members that must be set by the user, and others that are maintained by these routines, somewhat like a C++ class but with no encapsulation.

Three routines, wcsini(), wcssub(), and wcsfree() are provided to manage the wcsprm struct and another, wcsprt(), to prints its contents. Refer to the description of the wcsprm struct for an explanation of the anticipated usage of these routines. wcscopy(), which does a deep copy of one wcsprm struct to another, is defined as a preprocessor macro function that invokes wcssub().

wcsperr() prints the error message(s) (if any) stored in a wcsprm struct, and the linprm, celprm, prjprm, spcprm, and tabprm structs that it contains.

A setup routine, wcsset(), computes intermediate values in the wcsprm struct from parameters in it that were supplied by the user. The struct always needs to be set up by wcsset() but this need not be called explicitly - refer to the explanation of wcsprm::flag.

wcsp2s() and wcss2p() implement the WCS world coordinate transformations. In fact, they are high level driver routines for the WCS linear, logarithmic, celestial, spectral and tabular transformation routines described in lin.h, log.h, cel.h, spc.h and tab.h.

Given either the celestial longitude or latitude plus an element of the pixel coordinate a hybrid routine, wcsmix(), iteratively solves for the unknown elements.

wcssptr() translates the spectral axis in a wcsprm struct. For example, a 'FREQ' axis may be translated into 'ZOPT-F2W' and vice versa.

Quadcube projections:
The quadcube projections (TSC, CSC, QSC) may be represented in FITS in either of two ways:

a: The six faces may be laid out in one plane and numbered as follows:

                                  0
 
                         4  3  2  1  4  3  2
 
                                  5

Faces 2, 3 and 4 may appear on one side or the other (or both). The world-to-pixel routines map faces 2, 3 and 4 to the left but the pixel-to-world routines accept them on either side.

b: The "COBE" convention in which the six faces are stored in a three-dimensional structure using a CUBEFACE axis indexed from 0 to 5 as above.

These routines support both methods; wcsset() determines which is being used by the presence or absence of a CUBEFACE axis in ctype[]. wcsp2s() and wcss2p() translate the CUBEFACE axis representation to the single plane representation understood by the lower-level WCSLIB projection routines.

Define Documentation

#define WCSSUB_LONGITUDE 0x1001

Mask to use for extracting the longitude axis when sub-imaging, refer to the axes argument of wcssub().

#define WCSSUB_LATITUDE 0x1002

Mask to use for extracting the latitude axis when sub-imaging, refer to the axes argument of wcssub().

#define WCSSUB_CUBEFACE 0x1004

Mask to use for extracting the CUBEFACE axis when sub-imaging, refer to the axes argument of wcssub().

#define WCSSUB_CELESTIAL 0x1007

Mask to use for extracting the celestial axes (longitude, latitude and cubeface) when sub-imaging, refer to the axes argument of wcssub().

#define WCSSUB_SPECTRAL 0x1008

Mask to use for extracting the spectral axis when sub-imaging, refer to the axes argument of wcssub().

#define WCSSUB_STOKES 0x1010

Mask to use for extracting the STOKES axis when sub-imaging, refer to the axes argument of wcssub().

#define WCSLEN (sizeof(struct wcsprm)/sizeof(int))

Size of the wcsprm struct in int units, used by the Fortran wrappers.

#define wcscopy	(	alloc,
		wcssrc,
		wcsdst	)	wcssub(alloc, wcssrc, 0x0, 0x0, wcsdst)

wcscopy() does a deep copy of one wcsprm struct to another. As of WCSLIB 3.6, it is implemented as a preprocessor macro that invokes wcssub() with the nsub and axes pointers both set to zero.

#define wcsini_errmsg wcs_errmsg

Deprecated:: Added for backwards compatibility, use wcs_errmsg directly now instead.

#define wcssub_errmsg wcs_errmsg

Deprecated:: Added for backwards compatibility, use wcs_errmsg directly now instead.

#define wcscopy_errmsg wcs_errmsg

Deprecated:: Added for backwards compatibility, use wcs_errmsg directly now instead.

#define wcsfree_errmsg wcs_errmsg

Deprecated:: Added for backwards compatibility, use wcs_errmsg directly now instead.

#define wcsprt_errmsg wcs_errmsg

Deprecated:: Added for backwards compatibility, use wcs_errmsg directly now instead.

#define wcsset_errmsg wcs_errmsg

Deprecated:: Added for backwards compatibility, use wcs_errmsg directly now instead.

#define wcsp2s_errmsg wcs_errmsg

Deprecated:: Added for backwards compatibility, use wcs_errmsg directly now instead.

#define wcss2p_errmsg wcs_errmsg

Deprecated:: Added for backwards compatibility, use wcs_errmsg directly now instead.

#define wcsmix_errmsg wcs_errmsg

Deprecated:: Added for backwards compatibility, use wcs_errmsg directly now instead.

Enumeration Type Documentation

enum wcs_errmsg_enum

Enumerator:

WCSERR_SUCCESS
WCSERR_NULL_POINTER
WCSERR_MEMORY
WCSERR_SINGULAR_MTX
WCSERR_BAD_CTYPE
WCSERR_BAD_PARAM
WCSERR_BAD_COORD_TRANS
WCSERR_ILL_COORD_TRANS
WCSERR_BAD_PIX
WCSERR_BAD_WORLD
WCSERR_BAD_WORLD_COORD
WCSERR_NO_SOLUTION
WCSERR_BAD_SUBIMAGE
WCSERR_NON_SEPARABLE

Function Documentation

int wcsnpv ( int n )

wcsnpv() changes the value of NPVMAX (default 64). This global variable controls the number of PVi_ma keywords that wcsini() should allocate space for.

PLEASE NOTE: This function is not thread-safe.

Parameters:

[in] n Value of NPVMAX; ignored if < 0.

Returns:: Current value of NPVMAX.

int wcsnps ( int n )

wcsnps() changes the values of NPSMAX (default 8). This global variable controls the number of PSi_ma keywords that wcsini() should allocate space for.

PLEASE NOTE: This function is not thread-safe.

Parameters:

[in] n Value of NPSMAX; ignored if < 0.

Returns:: Current value of NPSMAX.

int wcsini	(	int	alloc,
		int	naxis,
		struct wcsprm *	wcs
	)

wcsini() optionally allocates memory for arrays in a wcsprm struct and sets all members of the struct to default values. Memory is allocated for up to NPVMAX PVi_ma keywords or NPSMAX PSi_ma keywords per WCS representation. These may be changed via wcsnpv() and wcsnps() before wcsini() is called.

PLEASE NOTE: every wcsprm struct should be initialized by wcsini(), possibly repeatedly. On the first invokation, and only the first invokation, wcsprm::flag must be set to -1 to initialize memory management, regardless of whether wcsini() will actually be used to allocate memory.

Parameters:

`[in]`	alloc	If true, allocate memory unconditionally for the crpix, etc. arrays. If false, it is assumed that pointers to these arrays have been set by the user except if they are null pointers in which case memory will be allocated for them regardless. (In other words, setting alloc true saves having to initalize these pointers to zero.)
`[in]`	naxis	The number of world coordinate axes. This is used to determine the length of the various wcsprm vectors and matrices and therefore the amount of memory to allocate for them.
`[in,out]`	wcs	Coordinate transformation parameters. Note that, in order to initialize memory management, wcsprm::flag should be set to -1 when wcs is initialized for the first time (memory leaks may result if it had already been initialized).

Returns:

Status return value:

0: Success.
1: Null wcsprm pointer passed.
2: Memory allocation failed.

For returns > 1, a detailed error message is set in wcsprm::err if enabled, see wcserr_enable().

int wcssub	(	int	alloc,
		const struct wcsprm *	wcssrc,
		int *	nsub,
		int	axes[],
		struct wcsprm *	wcsdst
	)

wcssub() extracts the coordinate description for a subimage from a wcsprm struct. It does a deep copy, using wcsini() to allocate memory for its arrays if required. Only the "information to be provided" part of the struct is extracted; a call to wcsset() is required to set up the remainder.

The world coordinate system of the subimage must be separable in the sense that the world coordinates at any point in the subimage must depend only on the pixel coordinates of the axes extracted. In practice, this means that the PCi_ja matrix of the original image must not contain non-zero off-diagonal terms that associate any of the subimage axes with any of the non-subimage axes.

Note that while the required elements of the tabprm array are extracted, the wtbarr array is not. (Thus it is not appropriate to call wcssub() after wcstab() but before filling the tabprm structs - refer to wcshdr.h.)

wcssub() can also add axes to a wcsprm struct. The new axes will be created using the defaults set by wcsini() which produce a simple, unnamed, linear axis with world coordinate equal to the pixel coordinate. These default values can be changed in before invoking wcsset().

Parameters:

`[in]`	alloc	If true, allocate memory for the crpix, etc. arrays in the destination. Otherwise, it is assumed that pointers to these arrays have been set by the user except if they are null pointers in which case memory will be allocated for them regardless.
`[in]`	wcssrc	Struct to extract from.
`[in,out]`	nsub
`[in,out]`	axes	Vector of length nsub containing the image axis numbers (1-relative) to extract. Order is significant; axes[0] is the axis number of the input image that corresponds to the first axis in the subimage, etc. Use an axis number of 0 to create a new axis using the defaults set by wcsini(). nsub (the pointer) may be set to zero, and so also may nsub, to indicate the number of axes in the input image; the number of axes will be returned if nsub != 0x0. axes itself (the pointer) may be set to zero to indicate the first nsub axes in their original order. Set both nsub and axes to zero to do a deep copy of one wcsprm struct to another. Subimage extraction by coordinate axis type may be done by setting the elements of axes[] to the following special preprocessor macro values: WCSSUB_LONGITUDE: Celestial longitude. WCSSUB_LATITUDE: Celestial latitude. WCSSUB_CUBEFACE: Quadcube `CUBEFACE` axis. WCSSUB_SPECTRAL: Spectral axis. WCSSUB_STOKES: Stokes axis. Refer to the notes (below) for further usage examples. On return, *nsub will contain the number of axes in the subimage; this may be zero if there were no axes of the required type(s) (in which case no memory will be allocated). axes[] will contain the axis numbers that were extracted, or 0 for newly created axes. The vector length must be sufficient to contain all axis numbers. No checks are performed to verify that the coordinate axes are consistent, this is done by wcsset().
`[in,out]`	wcsdst	Struct describing the subimage. wcsprm::flag should be set to -1 if wcsdst was not previously initialized (memory leaks may result if it was previously initialized).

Returns:

Status return value:

0: Success.
1: Null wcsprm pointer passed.
2: Memory allocation failed.
12: Invalid subimage specification.
13: Non-separable subimage coordinate system.

For returns > 1, a detailed error message is set in wcsprm::err if enabled, see wcserr_enable().

Notes:
Combinations of subimage axes of particular types may be extracted in the same order as they occur in the input image by combining preprocessor codes, for example

      *nsub = 1;
      axes[0] = WCSSUB_LONGITUDE | WCSSUB_LATITUDE | WCSSUB_SPECTRAL;

would extract the longitude, latitude, and spectral axes in the same order as the input image. If one of each were present, *nsub = 3 would be returned.

For convenience, WCSSUB_CELESTIAL is defined as the combination WCSSUB_LONGITUDE | WCSSUB_LATITUDE | WCSSUB_CUBEFACE.

The codes may also be negated to extract all but the types specified, for example

      *nsub = 4;
      axes[0] = WCSSUB_LONGITUDE;
      axes[1] = WCSSUB_LATITUDE;
      axes[2] = WCSSUB_CUBEFACE;
      axes[3] = -(WCSSUB_SPECTRAL | WCSSUB_STOKES);

The last of these specifies all axis types other than spectral or Stokes. Extraction is done in the order specified by axes[] a longitude axis (if present) would be extracted first (via axes[0]) and not subsequently (via axes[3]). Likewise for the latitude and cubeface axes in this example.

From the foregoing, it is apparent that the value of *nsub returned may be less than or greater than that given. However, it will never exceed the number of axes in the input image (plus the number of newly-created axes if any were specified on input).

int wcsfree ( struct wcsprm * wcs )

wcsfree() frees memory allocated for the wcsprm arrays by wcsini() and/or wcsset(). wcsini() records the memory it allocates and wcsfree() will only attempt to free this.

PLEASE NOTE: wcsfree() must not be invoked on a wcsprm struct that was not initialized by wcsini().

Parameters:

[out] wcs Coordinate transformation parameters.

Returns:

Status return value:

0: Success.
1: Null wcsprm pointer passed.

int wcsprt ( const struct wcsprm * wcs )

wcsprt() prints the contents of a wcsprm struct using wcsprintf(). Mainly intended for diagnostic purposes.

Parameters:

[in] wcs Coordinate transformation parameters.

Returns:

Status return value:

0: Success.
1: Null wcsprm pointer passed.

int wcsperr	(	const struct wcsprm *	wcs,
		const char *	prefix
	)

wcsperr() prints the error message(s), if any, stored in a wcsprm struct, and the linprm, celprm, prjprm, spcprm, and tabprm structs that it contains. If there are no errors then nothing is printed. It uses wcserr_prt(), q.v.

Parameters:

`[in]`	wcs	Coordinate transformation parameters.
`[in]`	prefix	If non-NULL, each output line will be prefixed with this string.

Returns:

Status return value:

0: Success.
1: Null wcsprm pointer passed.

int wcsset ( struct wcsprm * wcs )

wcsset() sets up a wcsprm struct according to information supplied within it (refer to the description of the wcsprm struct).

wcsset() recognizes the NCP projection and converts it to the equivalent SIN projection and likewise translates GLS into SFL. It also translates the AIPS spectral types ('FREQ-LSR', 'FELO-HEL', etc.), possibly changing the input header keywords wcsprm::ctype and/or wcsprm::specsys if necessary.

Note that this routine need not be called directly; it will be invoked by wcsp2s() and wcss2p() if the wcsprm::flag is anything other than a predefined magic value.

Parameters:

[in,out] wcs Coordinate transformation parameters.

Returns:

Status return value:

0: Success.
1: Null wcsprm pointer passed.
2: Memory allocation failed.
3: Linear transformation matrix is singular.
4: Inconsistent or unrecognized coordinate axis types.
5: Invalid parameter value.
6: Invalid coordinate transformation parameters.
7: Ill-conditioned coordinate transformation parameters.

For returns > 1, a detailed error message is set in wcsprm::err if enabled, see wcserr_enable().

int wcsp2s	(	struct wcsprm *	wcs,
		int	ncoord,
		int	nelem,
		const double	pixcrd[],
		double	imgcrd[],
		double	phi[],
		double	theta[],
		double	world[],
		int	stat[]
	)

wcsp2s() transforms pixel coordinates to world coordinates.

Parameters:

`[in,out]`	wcs	Coordinate transformation parameters.
`[in]`	ncoord,nelem	The number of coordinates, each of vector length nelem but containing wcs.naxis coordinate elements. Thus nelem must equal or exceed the value of the `NAXIS` keyword unless ncoord == 1, in which case nelem is not used.
`[in]`	pixcrd	Array of pixel coordinates.
`[out]`	imgcrd	Array of intermediate world coordinates. For celestial axes, imgcrd[][wcs.lng] and imgcrd[][wcs.lat] are the projected -, and -coordinates in pseudo "degrees". For spectral axes, imgcrd[][wcs.spec] is the intermediate spectral coordinate, in SI units.
`[out]`	phi,theta	Longitude and latitude in the native coordinate system of the projection [deg].
`[out]`	world	Array of world coordinates. For celestial axes, world[][wcs.lng] and world[][wcs.lat] are the celestial longitude and latitude [deg]. For spectral axes, imgcrd[][wcs.spec] is the intermediate spectral coordinate, in SI units.
`[out]`	stat	Status return value for each coordinate: 0: Success. 1+: A bit mask indicating invalid pixel coordinate element(s).

Returns:

Status return value:

0: Success.
1: Null wcsprm pointer passed.
2: Memory allocation failed.
3: Linear transformation matrix is singular.
4: Inconsistent or unrecognized coordinate axis types.
5: Invalid parameter value.
6: Invalid coordinate transformation parameters.
7: Ill-conditioned coordinate transformation parameters.
8: One or more of the pixel coordinates were invalid, as indicated by the stat vector.

For returns > 1, a detailed error message is set in wcsprm::err if enabled, see wcserr_enable().

int wcss2p	(	struct wcsprm *	wcs,
		int	ncoord,
		int	nelem,
		const double	world[],
		double	phi[],
		double	theta[],
		double	imgcrd[],
		double	pixcrd[],
		int	stat[]
	)

wcss2p() transforms world coordinates to pixel coordinates.

Parameters:

`[in,out]`	wcs	Coordinate transformation parameters.
`[in]`	ncoord,nelem	The number of coordinates, each of vector length nelem but containing wcs.naxis coordinate elements. Thus nelem must equal or exceed the value of the `NAXIS` keyword unless ncoord == 1, in which case nelem is not used.
`[in]`	world	Array of world coordinates. For celestial axes, world[][wcs.lng] and world[][wcs.lat] are the celestial longitude and latitude [deg]. For spectral axes, world[][wcs.spec] is the spectral coordinate, in SI units.
`[out]`	phi,theta	Longitude and latitude in the native coordinate system of the projection [deg].
`[out]`	imgcrd	Array of intermediate world coordinates. For celestial axes, imgcrd[][wcs.lng] and imgcrd[][wcs.lat] are the projected -, and -coordinates in pseudo "degrees". For quadcube projections with a `CUBEFACE` axis the face number is also returned in imgcrd[][wcs.cubeface]. For spectral axes, imgcrd[][wcs.spec] is the intermediate spectral coordinate, in SI units.
`[out]`	pixcrd	Array of pixel coordinates.
`[out]`	stat	Status return value for each coordinate: 0: Success. 1+: A bit mask indicating invalid world coordinate element(s).

Returns:

Status return value:

0: Success.
1: Null wcsprm pointer passed.
2: Memory allocation failed.
3: Linear transformation matrix is singular.
4: Inconsistent or unrecognized coordinate axis types.
5: Invalid parameter value.
6: Invalid coordinate transformation parameters.
7: Ill-conditioned coordinate transformation parameters.
9: One or more of the world coordinates were invalid, as indicated by the stat vector.

For returns > 1, a detailed error message is set in wcsprm::err if enabled, see wcserr_enable().

int wcsmix	(	struct wcsprm *	wcs,
		int	mixpix,
		int	mixcel,
		const double	vspan[],
		double	vstep,
		int	viter,
		double	world[],
		double	phi[],
		double	theta[],
		double	imgcrd[],
		double	pixcrd[]
	)

wcsmix(), given either the celestial longitude or latitude plus an element of the pixel coordinate, solves for the remaining elements by iterating on the unknown celestial coordinate element using wcss2p(). Refer also to the notes below.

Parameters:

`[in,out]`	wcs	Indices for the celestial coordinates obtained by parsing the wcsprm::ctype[].
`[in]`	mixpix	Which element of the pixel coordinate is given.
`[in]`	mixcel	Which element of the celestial coordinate is given: 1: Celestial longitude is given in world[wcs.lng], latitude returned in world[wcs.lat]. 2: Celestial latitude is given in world[wcs.lat], longitude returned in world[wcs.lng].
`[in]`	vspan	Solution interval for the celestial coordinate [deg]. The ordering of the two limits is irrelevant. Longitude ranges may be specified with any convenient normalization, for example [-120,+120] is the same as [240,480], except that the solution will be returned with the same normalization, i.e. lie within the interval specified.
`[in]`	vstep	Step size for solution search [deg]. If zero, a sensible, although perhaps non-optimal default will be used.
`[in]`	viter	If a solution is not found then the step size will be halved and the search recommenced. viter controls how many times the step size is halved. The allowed range is 5 - 10.
`[in,out]`	world	World coordinate elements. world[wcs.lng] and world[wcs.lat] are the celestial longitude and latitude [deg]. Which is given and which returned depends on the value of mixcel. All other elements are given.
`[out]`	phi,theta	Longitude and latitude in the native coordinate system of the projection [deg].
`[out]`	imgcrd	Image coordinate elements. imgcrd[wcs.lng] and imgcrd[wcs.lat] are the projected -, and -coordinates in pseudo "degrees".
`[in,out]`	pixcrd	Pixel coordinate. The element indicated by mixpix is given and the remaining elements are returned.

Returns:

Status return value:

0: Success.
1: Null wcsprm pointer passed.
2: Memory allocation failed.
3: Linear transformation matrix is singular.
4: Inconsistent or unrecognized coordinate axis types.
5: Invalid parameter value.
6: Invalid coordinate transformation parameters.
7: Ill-conditioned coordinate transformation parameters.
10: Invalid world coordinate.
11: No solution found in the specified interval.

For returns > 1, a detailed error message is set in wcsprm::err if enabled, see wcserr_enable().

Notes:
Initially the specified solution interval is checked to see if it's a "crossing" interval. If it isn't, a search is made for a crossing solution by iterating on the unknown celestial coordinate starting at the upper limit of the solution interval and decrementing by the specified step size. A crossing is indicated if the trial value of the pixel coordinate steps through the value specified. If a crossing interval is found then the solution is determined by a modified form of "regula falsi" division of the crossing interval. If no crossing interval was found within the specified solution interval then a search is made for a "non-crossing" solution as may arise from a point of tangency. The process is complicated by having to make allowance for the discontinuities that occur in all map projections.

Once one solution has been determined others may be found by subsequent invokations of wcsmix() with suitably restricted solution intervals.

Note the circumstance that arises when the solution point lies at a native pole of a projection in which the pole is represented as a finite curve, for example the zenithals and conics. In such cases two or more valid solutions may exist but wcsmix() only ever returns one.

Because of its generality wcsmix() is very compute-intensive. For compute-limited applications more efficient special-case solvers could be written for simple projections, for example non-oblique cylindrical projections.

int wcssptr	(	struct wcsprm *	wcs,
		int *	i,
		char	ctype[9]
	)

wcssptr() translates the spectral axis in a wcsprm struct. For example, a 'FREQ' axis may be translated into 'ZOPT-F2W' and vice versa.

Parameters:

`[in,out]`	wcs	Coordinate transformation parameters.
`[in,out]`	i	Index of the spectral axis (0-relative). If given < 0 it will be set to the first spectral axis identified from the ctype[] keyvalues in the wcsprm struct.
`[in,out]`	ctype	Desired spectral `CTYPEia`. Wildcarding may be used as for the ctypeS2 argument to spctrn() as described in the prologue of spc.h, i.e. if the final three characters are specified as "???", or if just the eighth character is specified as '?', the correct algorithm code will be substituted and returned.

Returns:

Status return value:

0: Success.
1: Null wcsprm pointer passed.
2: Memory allocation failed.
3: Linear transformation matrix is singular.
4: Inconsistent or unrecognized coordinate axis types.
5: Invalid parameter value.
6: Invalid coordinate transformation parameters.
7: Ill-conditioned coordinate transformation parameters.
12: Invalid subimage specification (no spectral axis).

For returns > 1, a detailed error message is set in wcsprm::err if enabled, see wcserr_enable().

Variable Documentation

const char * wcs_errmsg[]

Error messages to match the status value returned from each function.


Data Structures
struct	pvcard
	Store for `PVi_ma` keyrecords. More...
struct	pscard
	Store for `PSi_ma` keyrecords. More...
struct	wtbarr
	Extraction of coordinate lookup tables from BINTABLE. More...
struct	wcsprm
	Coordinate transformation parameters. More...
Defines
#define	WCSSUB_LONGITUDE 0x1001
	Mask for extraction of longitude axis by wcssub().
#define	WCSSUB_LATITUDE 0x1002
	Mask for extraction of latitude axis by wcssub().
#define	WCSSUB_CUBEFACE 0x1004
	Mask for extraction of `CUBEFACE` axis by wcssub().
#define	WCSSUB_CELESTIAL 0x1007
	Mask for extraction of celestial axes by wcssub().
#define	WCSSUB_SPECTRAL 0x1008
	Mask for extraction of spectral axis by wcssub().
#define	WCSSUB_STOKES 0x1010
	Mask for extraction of `STOKES` axis by wcssub().
#define	WCSLEN (sizeof(struct wcsprm)/sizeof(int))
	Size of the wcsprm struct in int units.
#define	wcscopy(alloc, wcssrc, wcsdst) wcssub(alloc, wcssrc, 0x0, 0x0, wcsdst)
	Copy routine for the wcsprm struct.
#define	wcsini_errmsg wcs_errmsg
	Deprecated.
#define	wcssub_errmsg wcs_errmsg
	Deprecated.
#define	wcscopy_errmsg wcs_errmsg
	Deprecated.
#define	wcsfree_errmsg wcs_errmsg
	Deprecated.
#define	wcsprt_errmsg wcs_errmsg
	Deprecated.
#define	wcsset_errmsg wcs_errmsg
	Deprecated.
#define	wcsp2s_errmsg wcs_errmsg
	Deprecated.
#define	wcss2p_errmsg wcs_errmsg
	Deprecated.
#define	wcsmix_errmsg wcs_errmsg
	Deprecated.
Enumerations
enum	wcs_errmsg_enum { WCSERR_SUCCESS = 0, WCSERR_NULL_POINTER = 1, WCSERR_MEMORY = 2, WCSERR_SINGULAR_MTX = 3, WCSERR_BAD_CTYPE = 4, WCSERR_BAD_PARAM = 5, WCSERR_BAD_COORD_TRANS = 6, WCSERR_ILL_COORD_TRANS = 7, WCSERR_BAD_PIX = 8, WCSERR_BAD_WORLD = 9, WCSERR_BAD_WORLD_COORD = 10, WCSERR_NO_SOLUTION = 11, WCSERR_BAD_SUBIMAGE = 12, WCSERR_NON_SEPARABLE = 13 }
Functions
int	wcsnpv (int n)
	Memory allocation for `PVi_ma`.
int	wcsnps (int n)
	Memory allocation for `PSi_ma`.
int	wcsini (int alloc, int naxis, struct wcsprm *wcs)
	Default constructor for the wcsprm struct.
int	wcssub (int alloc, const struct wcsprm wcssrc, int nsub, int axes[], struct wcsprm *wcsdst)
	Subimage extraction routine for the wcsprm struct.
int	wcsfree (struct wcsprm *wcs)
	Destructor for the wcsprm struct.
int	wcsprt (const struct wcsprm *wcs)
	Print routine for the wcsprm struct.
int	wcsperr (const struct wcsprm wcs, const char prefix)
	Print error messages from a wcsprm struct.
int	wcsset (struct wcsprm *wcs)
	Setup routine for the wcsprm struct.
int	wcsp2s (struct wcsprm *wcs, int ncoord, int nelem, const double pixcrd[], double imgcrd[], double phi[], double theta[], double world[], int stat[])
	Pixel-to-world transformation.
int	wcss2p (struct wcsprm *wcs, int ncoord, int nelem, const double world[], double phi[], double theta[], double imgcrd[], double pixcrd[], int stat[])
	World-to-pixel transformation.
int	wcsmix (struct wcsprm *wcs, int mixpix, int mixcel, const double vspan[], double vstep, int viter, double world[], double phi[], double theta[], double imgcrd[], double pixcrd[])
	Hybrid coordinate transformation.
int	wcssptr (struct wcsprm wcs, int i, char ctype[9])
	Spectral axis translation.
Variables
const char *	wcs_errmsg []
	Status return messages.