wcshdr.h File Reference

#include "wcs.h"

Go to the source code of this file.

Macros
#define	WCSHDR_none   0x00000000
	Bit mask for wcspih() and wcsbth() - reject all extensions. More...
#define	WCSHDR_all   0x000FFFFF
	Bit mask for wcspih() and wcsbth() - accept all extensions. More...
#define	WCSHDR_reject   0x10000000
	Bit mask for wcspih() and wcsbth() - reject non-standard keywords. More...
#define	WCSHDR_CROTAia   0x00000001
	Bit mask for wcspih() and wcsbth() - accept CROTAia, iCROTna, TCROTna. More...
#define	WCSHDR_EPOCHa   0x00000002
	Bit mask for wcspih() and wcsbth() - accept EPOCHa. More...
#define	WCSHDR_VELREFa   0x00000004
	Bit mask for wcspih() and wcsbth() - accept VELREFa. More...
#define	WCSHDR_CD00i00j   0x00000008
	Bit mask for wcspih() and wcsbth() - accept CD00i00j. More...
#define	WCSHDR_PC00i00j   0x00000010
	Bit mask for wcspih() and wcsbth() - accept PC00i00j. More...
#define	WCSHDR_PROJPn   0x00000020
	Bit mask for wcspih() and wcsbth() - accept PROJPn. More...
#define	WCSHDR_RADECSYS   0x00000040
	Bit mask for wcspih() and wcsbth() - accept RADECSYS. More...
#define	WCSHDR_VSOURCE   0x00000080
	Bit mask for wcspih() and wcsbth() - accept VSOURCEa. More...
#define	WCSHDR_DOBSn   0x00000100
	Bit mask for wcspih() and wcsbth() - accept DOBSn. More...
#define	WCSHDR_LONGKEY   0x00000200
	Bit mask for wcspih() and wcsbth() - accept long forms of the alternate binary table and pixel list WCS keywords. More...
#define	WCSHDR_CNAMn   0x00000400
	Bit mask for wcspih() and wcsbth() - accept iCNAMn, TCNAMn, iCRDEn, TCRDEn, iCSYEn, TCSYEn. More...
#define	WCSHDR_AUXIMG   0x00000800
	Bit mask for wcspih() and wcsbth() - allow the image-header form of an auxiliary WCS keyword to provide a default value for all images. More...
#define	WCSHDR_ALLIMG   0x00001000
	Bit mask for wcspih() and wcsbth() - allow the image-header form of all image header WCS keywords to provide a default value for all images. More...
#define	WCSHDR_IMGHEAD   0x00010000
	Bit mask for wcsbth() - restrict to image header keywords only. More...
#define	WCSHDR_BIMGARR   0x00020000
	Bit mask for wcsbth() - restrict to binary table image array keywords only. More...
#define	WCSHDR_PIXLIST   0x00040000
	Bit mask for wcsbth() - restrict to pixel list keywords only. More...
#define	WCSHDO_none   0x00
	Bit mask for wcshdo() - don't write any extensions. More...
#define	WCSHDO_all   0xFF
	Bit mask for wcshdo() - write all extensions. More...
#define	WCSHDO_safe   0x0F
	Bit mask for wcshdo() - write safe extensions only. More...
#define	WCSHDO_DOBSn   0x01
	Bit mask for wcshdo() - write DOBSn. More...
#define	WCSHDO_TPCn_ka   0x02
	Bit mask for wcshdo() - write TPCn_ka. More...
#define	WCSHDO_PVn_ma   0x04
	Bit mask for wcshdo() - write iPVn_ma, TPVn_ma, iPSn_ma, TPSn_ma. More...
#define	WCSHDO_CRPXna   0x08
	Bit mask for wcshdo() - write jCRPXna, TCRPXna, iCDLTna, TCDLTna, iCUNIna, TCUNIna, iCTYPna, TCTYPna, iCRVLna, TCRVLna. More...
#define	WCSHDO_CNAMna   0x10
	Bit mask for wcshdo() - write iCNAMna, TCNAMna, iCRDEna, TCRDEna, iCSYEna, TCSYEna. More...
#define	WCSHDO_WCSNna   0x20
	Bit mask for wcshdo() - write WCSNna instead of TWCSna More...

Enumerations
enum	wcshdr_errmsg_enum {   WCSHDRERR_SUCCESS = 0, WCSHDRERR_NULL_POINTER = 1, WCSHDRERR_MEMORY = 2, WCSHDRERR_BAD_COLUMN = 3,   WCSHDRERR_PARSER = 4, WCSHDRERR_BAD_TABULAR_PARAMS = 5 }

Functions
int	wcspih (char *header, int nkeyrec, int relax, int ctrl, int *nreject, int *nwcs, struct wcsprm **wcs)
	FITS WCS parser routine for image headers. More...
int	wcsbth (char *header, int nkeyrec, int relax, int ctrl, int keysel, int *colsel, int *nreject, int *nwcs, struct wcsprm **wcs)
	FITS WCS parser routine for binary table and image headers. More...
int	wcstab (struct wcsprm *wcs)
	Tabular construction routine. More...
int	wcsidx (int nwcs, struct wcsprm **wcs, int alts[27])
	Index alternate coordinate representations. More...
int	wcsbdx (int nwcs, struct wcsprm **wcs, int type, short alts[1000][28])
	Index alternate coordinate representions. More...
int	wcsvfree (int *nwcs, struct wcsprm **wcs)
	Free the array of wcsprm structs. More...
int	wcshdo (int relax, struct wcsprm *wcs, int *nkeyrec, char **header)
	Write out a wcsprm struct as a FITS header. More...

Variables
const char *	wcshdr_errmsg []
	Status return messages. More...

Detailed Description

Routines in this suite are aimed at extracting WCS information from a FITS file. They provide the high-level interface between the FITS file and the WCS coordinate transformation routines.

Additionally, function wcshdo() is provided to write out the contents of a wcsprm struct as a FITS header.

Briefly, the anticipated sequence of operations is as follows:

• 1: Open the FITS file and read the image or binary table header, e.g. using CFITSIO routine fits_hdr2str().

• 2: Parse the header using wcspih() or wcsbth(); they will automatically interpret 'TAB' header keywords using wcstab().

• 3: Allocate memory for, and read 'TAB' arrays from the binary table extension, e.g. using CFITSIO routine fits_read_wcstab() - refer to the prologue of getwcstab.h. wcsset() will automatically take control of this allocated memory, in particular causing it to be free'd by wcsfree().

• 4: Translate non-standard WCS usage using wcsfix(), see wcsfix.h.

• 5: Initialize wcsprm struct(s) using wcsset() and calculate coordinates using wcsp2s() and/or wcss2p(). Refer to the prologue of wcs.h for a description of these and other high-level WCS coordinate transformation routines.

• 6: Clean up by freeing memory with wcsvfree().

In detail:

• wcspih() is a high-level FITS WCS routine that parses an image header. It returns an array of up to 27 wcsprm structs on each of which it invokes wcstab().
• wcsbth() is the analogue of wcspih() for use with binary tables; it handles image array and pixel list keywords. As an extension of the FITS WCS standard, it also recognizes image header keywords which may be used to provide default values via an inheritance mechanism.
• wcstab() assists in filling in members of the wcsprm struct associated with coordinate lookup tables ('TAB'). These are based on arrays stored in a FITS binary table extension (BINTABLE) that are located by PVi_ma keywords in the image header.
• wcsidx() and wcsbdx() are utility routines that return the index for a specified alternate coordinate descriptor in the array of wcsprm structs returned by wcspih() or wcsbth().
• wcsvfree() deallocates memory for an array of wcsprm structs, such as returned by wcspih() or wcsbth().
• wcshdo() writes out a wcsprm struct as a FITS header.

Macro Definition Documentation

#define WCSHDR_none   0x00000000

Bit mask for the relax argument of wcspih() and wcsbth() - reject all extensions.

Refer to wcsbth() note 5.

#define WCSHDR_all   0x000FFFFF

Bit mask for the relax argument of wcspih() and wcsbth() - accept all extensions.

Refer to wcsbth() note 5.

#define WCSHDR_reject   0x10000000

Bit mask for the relax argument of wcspih() and wcsbth() - reject non-standard keywords.

Refer to wcsbth() note 5.

#define WCSHDR_CROTAia   0x00000001

Bit mask for the relax argument of wcspih() and wcsbth() - accept CROTAia, iCROTna, TCROTna.

Refer to wcsbth() note 5.

#define WCSHDR_EPOCHa   0x00000002

Bit mask for the relax argument of wcspih() and wcsbth() - accept EPOCHa.

Refer to wcsbth() note 5.

#define WCSHDR_VELREFa   0x00000004

Bit mask for the relax argument of wcspih() and wcsbth() - accept VELREFa.

Refer to wcsbth() note 5.

#define WCSHDR_CD00i00j   0x00000008

Bit mask for the relax argument of wcspih() and wcsbth() - accept CD00i00j.

Refer to wcsbth() note 5.

#define WCSHDR_PC00i00j   0x00000010

Bit mask for the relax argument of wcspih() and wcsbth() - accept PC00i00j.

Refer to wcsbth() note 5.

#define WCSHDR_PROJPn   0x00000020

Bit mask for the relax argument of wcspih() and wcsbth() - accept PROJPn.

Refer to wcsbth() note 5.

#define WCSHDR_RADECSYS   0x00000040

Bit mask for the relax argument of wcspih() and wcsbth() - accept RADECSYS.

Refer to wcsbth() note 5.

#define WCSHDR_VSOURCE   0x00000080

Bit mask for the relax argument of wcspih() and wcsbth() - accept VSOURCEa.

Refer to wcsbth() note 5.

#define WCSHDR_DOBSn   0x00000100

Bit mask for the relax argument of wcspih() and wcsbth() - accept DOBSn.

Refer to wcsbth() note 5.

#define WCSHDR_LONGKEY   0x00000200

Bit mask for the relax argument of wcspih() and wcsbth() - accept long forms of the alternate binary table and pixel list WCS keywords.

Refer to wcsbth() note 5.

#define WCSHDR_CNAMn   0x00000400

Bit mask for the relax argument of wcspih() and wcsbth() - accept iCNAMn, TCNAMn, iCRDEn, TCRDEn, iCSYEn, TCSYEn.

Refer to wcsbth() note 5.

#define WCSHDR_AUXIMG   0x00000800

Bit mask for the relax argument of wcspih() and wcsbth() - allow the image-header form of an auxiliary WCS keyword with representation-wide scope to provide a default value for all images.

Refer to wcsbth() note 5.

#define WCSHDR_ALLIMG   0x00001000

Bit mask for the relax argument of wcspih() and wcsbth() - allow the image-header form of all image header WCS keywords to provide a default value for all image arrays in a binary table (n.b. not pixel list).

Refer to wcsbth() note 5.

#define WCSHDR_IMGHEAD   0x00010000

Bit mask for the keysel argument of wcsbth() - restrict keyword types considered to image header keywords only.

#define WCSHDR_BIMGARR   0x00020000

Bit mask for the keysel argument of wcsbth() - restrict keyword types considered to binary table image array keywords only.

#define WCSHDR_PIXLIST   0x00040000

Bit mask for the keysel argument of wcsbth() - restrict keyword types considered to pixel list keywords only.

#define WCSHDO_none   0x00

Bit mask for the relax argument of wcshdo() - don't write any extensions.

Refer to the notes for wcshdo().

#define WCSHDO_all   0xFF

Bit mask for the relax argument of wcshdo() - write all extensions.

Refer to the notes for wcshdo().

#define WCSHDO_safe   0x0F

Bit mask for the relax argument of wcshdo() - write only extensions that are considered safe.

Refer to the notes for wcshdo().

#define WCSHDO_DOBSn   0x01

Bit mask for the relax argument of wcshdo() - write DOBSn, the column-specific analogue of DATE-OBS for use in binary tables and pixel lists.

Refer to the notes for wcshdo().

#define WCSHDO_TPCn_ka   0x02

Bit mask for the relax argument of wcshdo() - write TPCn_ka if less than eight characters instead of TPn_ka.

Refer to the notes for wcshdo().

#define WCSHDO_PVn_ma   0x04

Bit mask for the relax argument of wcshdo() - write iPVn_ma, TPVn_ma, iPSn_ma, TPSn_ma, if less than eight characters instead of iVn_ma, TVn_ma, iSn_ma, TSn_ma.

Refer to the notes for wcshdo().

#define WCSHDO_CRPXna   0x08

Bit mask for the relax argument of wcshdo() - write jCRPXna, TCRPXna, iCDLTna, TCDLTna, iCUNIna, TCUNIna, iCTYPna, TCTYPna, iCRVLna, TCRVLna, if less than eight characters instead of jCRPna, TCRPna, iCDEna, TCDEna, iCUNna, TCUNna, iCTYna, TCTYna, iCRVna, TCRVna.

Refer to the notes for wcshdo().

#define WCSHDO_CNAMna   0x10

Bit mask for the relax argument of wcshdo() - write iCNAMna, TCNAMna, iCRDEna, TCRDEna, iCSYEna, TCSYEna, if less than eight characters instead of iCNAna, TCNAna, iCRDna, TCRDna, iCSYna, TCSYna.

Refer to the notes for wcshdo().

#define WCSHDO_WCSNna   0x20

Bit mask for the relax argument of wcshdo() - write WCSNna instead of TWCSna.

Refer to the notes for wcshdo().

Enumeration Type Documentation

enum wcshdr_errmsg_enum

Enumerator
WCSHDRERR_SUCCESS
WCSHDRERR_NULL_POINTER
WCSHDRERR_MEMORY
WCSHDRERR_BAD_COLUMN
WCSHDRERR_PARSER
WCSHDRERR_BAD_TABULAR_PARAMS

Function Documentation

int wcspih	(	char *	header,
		int	nkeyrec,
		int	relax,
		int	ctrl,
		int *	nreject,
		int *	nwcs,
		struct wcsprm **	wcs
	)

wcspih() is a high-level FITS WCS routine that parses an image header, either that of a primary HDU or of an image extension. All WCS keywords defined in Papers I, II, and III are recognized, and also those used by the AIPS convention and certain other keywords that existed in early drafts of the WCS papers as explained in wcsbth() note 5.

Given a character array containing a FITS image header, wcspih() identifies and reads all WCS keywords for the primary coordinate representation and up to 26 alternate representations. It returns this information as an array of wcsprm structs.

wcspih() invokes wcstab() on each of the wcsprm structs that it returns.

Use wcsbth() in preference to wcspih() for FITS headers of unknown type; wcsbth() can parse image headers as well as binary table and pixel list headers.

Parameters

[in,out]	header	Character array containing the (entire) FITS image header from which to identify and construct the coordinate representations, for example, as might be obtained conveniently via the CFITSIO routine fits_hdr2str(). Each header "keyrecord" (formerly "card image") consists of exactly 80 7-bit ASCII printing characters in the range 0x20 to 0x7e (which excludes NUL, BS, TAB, LF, FF and CR) especially noting that the keyrecords are NOT null-terminated. For negative values of ctrl (see below), header[] is modified so that WCS keyrecords processed by wcspih() are removed from it.
[in]	nkeyrec	Number of keyrecords in header[].
[in]	relax	Degree of permissiveness: 0: Recognize only FITS keywords defined by the published WCS standard. WCSHDR_all: Admit all recognized informal extensions of the WCS standard. Fine-grained control of the degree of permissiveness is also possible as explained in wcsbth() note 5.
[in]	ctrl	Error reporting and other control options for invalid WCS and other header keyrecords: 0: Do not report any rejected header keyrecords. 1: Produce a one-line message stating the number of WCS keyrecords rejected (nreject). 2: Report each rejected keyrecord and the reason why it was rejected. 3: As above, but also report all non-WCS keyrecords that were discarded, and the number of coordinate representations (nwcs) found. The report is written to stderr by default, or the stream set by wcsprintf_set(). For ctrl < 0, WCS keyrecords processed by wcspih() are removed from header[]: -1: Remove only valid WCS keyrecords whose values were successfully extracted, nothing is reported. -2: Also remove WCS keyrecords that were rejected, reporting each one and the reason that it was rejected. -3: As above, and also report the number of coordinate representations (nwcs) found. -11: Same as -1 but preserving the basic keywords '{DATE,MJD}-{OBS,AVG}' and 'OBSGEO-{X,Y,Z}'. If any keyrecords are removed from header[] it will be null-terminated (NUL not being a legal FITS header character), otherwise it will contain its original complement of nkeyrec keyrecords and possibly not be null-terminated.
[out]	nreject	Number of WCS keywords rejected for syntax errors, illegal values, etc. Keywords not recognized as WCS keywords are simply ignored. Refer also to wcsbth() note 5.
[out]	nwcs	Number of coordinate representations found.
[out]	wcs	Pointer to an array of wcsprm structs containing up to 27 coordinate representations. Memory for the array is allocated by wcspih() which also invokes wcsini() for each struct to allocate memory for internal arrays and initialize their members to default values. Refer also to wcsbth() note 8. Note that wcsset() is not invoked on these structs. This allocated memory must be freed by the user, first by invoking wcsfree() for each struct, and then by freeing the array itself. A routine, wcsvfree(), is provided to do this (see below).

Returns

Status return value:

• 0: Success.
• 1: Null wcsprm pointer passed.
• 2: Memory allocation failed.
• 4: Fatal error returned by Flex parser.

Notes:
Refer to wcsbth() notes 1, 2, 3, 5, 7, and 8.

int wcsbth	(	char *	header,
		int	nkeyrec,
		int	relax,
		int	ctrl,
		int	keysel,
		int *	colsel,
		int *	nreject,
		int *	nwcs,
		struct wcsprm **	wcs
	)

wcsbth() is a high-level FITS WCS routine that parses a binary table header. It handles image array and pixel list WCS keywords which may be present together in one header.

As an extension of the FITS WCS standard, wcsbth() also recognizes image header keywords in a binary table header. These may be used to provide default values via an inheritance mechanism discussed in note 5 (c.f. WCSHDR_AUXIMG and WCSHDR_ALLIMG), or may instead result in wcsprm structs that are not associated with any particular column. Thus wcsbth() can handle primary image and image extension headers in addition to binary table headers (it ignores NAXIS and does not rely on the presence of the TFIELDS keyword).

All WCS keywords defined in Papers I, II, and III are recognized, and also those used by the AIPS convention and certain other keywords that existed in early drafts of the WCS papers as explained in note 5 below.

wcsbth() sets the colnum or colax[] members of the wcsprm structs that it returns with the column number of an image array or the column numbers associated with each pixel coordinate element in a pixel list. wcsprm structs that are not associated with any particular column, as may be derived from image header keywords, have colnum == 0.

Note 6 below discusses the number of wcsprm structs returned by wcsbth(), and the circumstances in which image header keywords cause a struct to be created. See also note 9 concerning the number of separate images that may be stored in a pixel list.

The API to wcsbth() is similar to that of wcspih() except for the addition of extra arguments that may be used to restrict its operation. Like wcspih(), wcsbth() invokes wcstab() on each of the wcsprm structs that it returns.

Parameters

[in,out]	header	Character array containing the (entire) FITS binary table, primary image, or image extension header from which to identify and construct the coordinate representations, for example, as might be obtained conveniently via the CFITSIO routine fits_hdr2str(). Each header "keyrecord" (formerly "card image") consists of exactly 80 7-bit ASCII printing characters in the range 0x20 to 0x7e (which excludes NUL, BS, TAB, LF, FF and CR) especially noting that the keyrecords are NOT null-terminated. For negative values of ctrl (see below), header[] is modified so that WCS keyrecords processed by wcsbth() are removed from it.
[in]	nkeyrec	Number of keyrecords in header[].
[in]	relax	Degree of permissiveness: 0: Recognize only FITS keywords defined by the published WCS standard. WCSHDR_all: Admit all recognized informal extensions of the WCS standard. Fine-grained control of the degree of permissiveness is also possible, as explained in note 5 below.
[in]	ctrl	Error reporting and other control options for invalid WCS and other header keyrecords: 0: Do not report any rejected header keyrecords. 1: Produce a one-line message stating the number of WCS keyrecords rejected (nreject). 2: Report each rejected keyrecord and the reason why it was rejected. 3: As above, but also report all non-WCS keyrecords that were discarded, and the number of coordinate representations (nwcs) found. The report is written to stderr by default, or the stream set by wcsprintf_set(). For ctrl < 0, WCS keyrecords processed by wcsbth() are removed from header[]: -1: Remove only valid WCS keyrecords whose values were successfully extracted, nothing is reported. -2: Also remove WCS keyrecords that were rejected, reporting each one and the reason that it was rejected. -3: As above, and also report the number of coordinate representations (nwcs) found. -11: Same as -1 but preserving the basic keywords '{DATE,MJD}-{OBS,AVG}' and 'OBSGEO-{X,Y,Z}'. If any keyrecords are removed from header[] it will be null-terminated (NUL not being a legal FITS header character), otherwise it will contain its original complement of nkeyrec keyrecords and possibly not be null-terminated.
[in]	keysel	Vector of flag bits that may be used to restrict the keyword types considered: WCSHDR_IMGHEAD: Image header keywords. WCSHDR_BIMGARR: Binary table image array. WCSHDR_PIXLIST: Pixel list keywords. If zero, there is no restriction. Keywords such as EQUIna or RFRQna that are common to binary table image arrays and pixel lists (including WCSNna and TWCSna, as explained in note 4 below) are selected by both WCSHDR_BIMGARR and WCSHDR_PIXLIST. Thus if inheritance via WCSHDR_ALLIMG is enabled as discussed in note 5 and one of these shared keywords is present, then WCSHDR_IMGHEAD and WCSHDR_PIXLIST alone may be sufficient to cause the construction of coordinate descriptions for binary table image arrays.
[in]	colsel	Pointer to an array of table column numbers used to restrict the keywords considered by wcsbth(). A null pointer may be specified to indicate that there is no restriction. Otherwise, the magnitude of cols[0] specifies the length of the array: cols[0] > 0: the columns are included, cols[0] < 0: the columns are excluded. For the pixel list keywords TPn_ka and TCn_ka (and TPCn_ka and TCDn_ka if WCSHDR_LONGKEY is enabled), it is an error for one column to be selected but not the other. This is unlike the situation with invalid keyrecords, which are simply rejected, because the error is not intrinsic to the header itself but arises in the way that it is processed.
[out]	nreject	Number of WCS keywords rejected for syntax errors, illegal values, etc. Keywords not recognized as WCS keywords are simply ignored, refer also to note 5 below.
[out]	nwcs	Number of coordinate representations found.
[out]	wcs	Pointer to an array of wcsprm structs containing up to 27027 coordinate representations, refer to note 6 below. Memory for the array is allocated by wcsbth() which also invokes wcsini() for each struct to allocate memory for internal arrays and initialize their members to default values. Refer also to note 8 below. Note that wcsset() is not invoked on these structs. This allocated memory must be freed by the user, first by invoking wcsfree() for each struct, and then by freeing the array itself. A routine, wcsvfree(), is provided to do this (see below).

Returns

Status return value:

• 0: Success.
• 1: Null wcsprm pointer passed.
• 2: Memory allocation failed.
• 3: Invalid column selection.
• 4: Fatal error returned by Flex parser.

Notes:

1. wcspih() determines the number of coordinate axes independently for each alternate coordinate representation (denoted by the "a" value in keywords like CTYPEia) from the higher of

   1. NAXIS,
   2. WCSAXESa,
   3. The highest axis number in any parameterized WCS keyword. The keyvalue, as well as the keyword, must be syntactically valid otherwise it will not be considered.

   If none of these keyword types is present, i.e. if the header only contains auxiliary WCS keywords for a particular coordinate representation, then no coordinate description is constructed for it.

   wcsbth() is similar except that it ignores the NAXIS keyword if given an image header to process.

   The number of axes, which is returned as a member of the wcsprm struct, may differ for different coordinate representations of the same image.

2. wcspih() and wcsbth() enforce correct FITS "keyword = value" syntax with regard to "= " occurring in columns 9 and 10.

   However, they do recognize free-format character (NOST 100-2.0, Sect. 5.2.1), integer (Sect. 5.2.3), and floating-point values (Sect. 5.2.4) for all keywords.

3. Where CROTAn, CDi_ja, and PCi_ja occur together in one header wcspih() and wcsbth() treat them as described in the prologue to wcs.h.

4. WCS Paper I mistakenly defined the pixel list form of WCSNAMEa as TWCSna instead of WCSNna; the 'T' is meant to substitute for the axis number in the binary table form of the keyword - note that keywords defined in WCS Papers II and III that are not parameterised by axis number have identical forms for binary tables and pixel lists. Consequently wcsbth() always treats WCSNna and TWCSna as equivalent.

5. wcspih() and wcsbth() interpret the relax argument as a vector of flag bits to provide fine-grained control over what non-standard WCS keywords to accept. The flag bits are subject to change in future and should be set by using the preprocessor macros (see below) for the purpose.

   • WCSHDR_none: Don't accept any extensions (not even those in the errata). Treat non-conformant keywords in the same way as non-WCS keywords in the header, i.e. simply ignore them.

   • WCSHDR_all: Accept all extensions recognized by the parser.

   • WCSHDR_reject: Reject non-standard keywords (that are not otherwise accepted). A message will optionally be printed on stderr by default, or the stream set by wcsprintf_set(), as determined by the ctrl argument, and nreject will be incremented.

     This flag may be used to signal the presence of non-standard keywords, otherwise they are simply passed over as though they did not exist in the header.

     Useful for testing conformance of a FITS header to the WCS standard.

   • WCSHDR_CROTAia: Accept CROTAia (wcspih()), iCROTna (wcsbth()), TCROTna (wcsbth()).
   • WCSHDR_EPOCHa: Accept EPOCHa.

   • WCSHDR_VELREFa: Accept VELREFa. wcspih() always recognizes the AIPS-convention keywords, CROTAn, EPOCH, and VELREF for the primary representation (a = ' ') but alternates are non-standard.

     wcsbth() accepts EPOCHa and VELREFa only if WCSHDR_AUXIMG is also enabled.

   • WCSHDR_CD00i00j: Accept CD00i00j (wcspih()).
   • WCSHDR_PC00i00j: Accept PC00i00j (wcspih()).

   • WCSHDR_PROJPn: Accept PROJPn (wcspih()). These appeared in early drafts of WCS Paper I+II (before they were split) and are equivalent to CDi_ja, PCi_ja, and PVi_ma for the primary representation (a = ' '). PROJPn is equivalent to PVi_ma with m = n 9, and is associated exclusively with the latitude axis.

   • WCSHDR_RADECSYS: Accept RADECSYS. This appeared in early drafts of WCS Paper I+II and was subsequently replaced by RADESYSa.

     wcsbth() accepts RADECSYS only if WCSHDR_AUXIMG is also enabled.

   • WCSHDR_VSOURCE: Accept VSOURCEa or VSOUna (wcsbth()). This appeared in early drafts of WCS Paper III and was subsequently dropped in favour of ZSOURCEa and ZSOUna.

     wcsbth() accepts VSOURCEa only if WCSHDR_AUXIMG is also enabled.

   • WCSHDR_DOBSn (wcsbth() only): Allow DOBSn, the column-specific analogue of DATE-OBS. By an oversight this was never formally defined in the standard.

   • WCSHDR_LONGKEY (wcsbth() only): Accept long forms of the alternate binary table and pixel list WCS keywords, i.e. with "a" non- blank. Specifically

     ---

     jCRPXna	TCRPXna	:	jCRPXn	jCRPna	TCRPXn	TCRPna	CRPIXja
     	TPCn_ka	:		ijPCna		TPn_ka	PCi_ja
     	TCDn_ka	:		ijCDna		TCn_ka	CDi_ja
     iCDLTna	TCDLTna	:	iCDLTn	iCDEna	TCDLTn	TCDEna	CDELTia
     iCUNIna	TCUNIna	:	iCUNIn	iCUNna	TCUNIn	TCUNna	CUNITia
     iCTYPna	TCTYPna	:	iCTYPn	iCTYna	TCTYPn	TCTYna	CTYPEia
     iCRVLna	TCRVLna	:	iCRVLn	iCRVna	TCRVLn	TCRVna	CRVALia
     iPVn_ma	TPVn_ma	:		iVn_ma		TVn_ma	PVi_ma
     iPSn_ma	TPSn_ma	:		iSn_ma		TSn_ma	PSi_ma

     ---

     where the primary and standard alternate forms together with the image-header equivalent are shown rightwards of the colon.

     The long form of these keywords could be described as quasi- standard. TPCn_ka, iPVn_ma, and TPVn_ma appeared by mistake in the examples in WCS Paper II and subsequently these and also TCDn_ka, iPSn_ma and TPSn_ma were legitimized by the errata to the WCS papers.

     Strictly speaking, the other long forms are non-standard and in fact have never appeared in any draft of the WCS papers nor in the errata. However, as natural extensions of the primary form they are unlikely to be written with any other intention. Thus it should be safe to accept them provided, of course, that the resulting keyword does not exceed the 8-character limit.

     If WCSHDR_CNAMn is enabled then also accept

     ---

     iCNAMna	TCNAMna	:	—	iCNAna	—	TCNAna	CNAMEia
     iCRDEna	TCRDEna	:	—	iCRDna	—	TCRDna	CRDERia
     iCSYEna	TCSYEna	:	—	iCSYna	—	TCSYna	CSYERia

     ---

     Note that CNAMEia, CRDERia, CSYERia, and their variants are not used by WCSLIB but are stored in the wcsprm struct as auxiliary information.

   • WCSHDR_CNAMn (wcsbth() only): Accept iCNAMn, iCRDEn, iCSYEn, TCNAMn, TCRDEn, and TCSYEn, i.e. with "a" blank. While non-standard, these are the obvious analogues of iCTYPn, TCTYPn, etc.

   • WCSHDR_AUXIMG (wcsbth() only): Allow the image-header form of an auxiliary WCS keyword with representation-wide scope to provide a default value for all images. This default may be overridden by the column-specific form of the keyword.

     For example, a keyword like EQUINOXa would apply to all image arrays in a binary table, or all pixel list columns with alternate representation "a" unless overridden by EQUIna.

     Specifically the keywords are:

     ---

     LATPOLEa	for LATPna
     LONPOLEa	for LONPna
     RESTFREQ	for RFRQna
     RESTFRQa	for RFRQna
     RESTWAVa	for RWAVna

     ---

     whose keyvalues are actually used by WCSLIB, and also keywords that provide auxiliary information that is simply stored in the wcsprm struct:

     ---

     EPOCH		... (No column-specific form.)
     EPOCHa		... Only if WCSHDR_EPOCHa is set.
     EQUINOXa	for EQUIna
     RADESYSa	for RADEna
     RADECSYS	for RADEna	... Only if WCSHDR_RADECSYS is set.
     SPECSYSa	for SPECna
     SSYSOBSa	for SOBSna
     SSYSSRCa	for SSRCna
     VELOSYSa	for VSYSna
     VELANGLa	for VANGna
     VELREF		... (No column-specific form.)
     VELREFa		... Only if WCSHDR_VELREFa is set.
     VSOURCEa	for VSOUna	... Only if WCSHDR_VSOURCE is set.
     WCSNAMEa	for WCSNna	... Or TWCSna (see below).
     ZSOURCEa	for ZSOUna

     ---

     ---

     DATE-AVG	for DAVGn
     DATE-OBS	for DOBSn
     MJD-AVG	for MJDAn
     MJD-OBS	for MJDOBn
     OBSGEO-X	for OBSGXn
     OBSGEO-Y	for OBSGYn
     OBSGEO-Z	for OBSGZn

     ---

     where the image-header keywords on the left provide default values for the column specific keywords on the right.

     Keywords in the last group, such as MJD-OBS, apply to all alternate representations, so MJD-OBS would provide a default value for all images in the header.

     This auxiliary inheritance mechanism applies to binary table image arrays and pixel lists alike. Most of these keywords have no default value, the exceptions being LONPOLEa and LATPOLEa, and also RADESYSa and EQUINOXa which provide defaults for each other. Thus the only potential difficulty in using WCSHDR_AUXIMG is that of erroneously inheriting one of these four keywords.

     Unlike WCSHDR_ALLIMG, the existence of one (or all) of these auxiliary WCS image header keywords will not by itself cause a wcsprm struct to be created for alternate representation "a". This is because they do not provide sufficient information to create a non-trivial coordinate representation when used in conjunction with the default values of those keywords, such as CTYPEia, that are parameterized by axis number.

   • WCSHDR_ALLIMG (wcsbth() only): Allow the image-header form of *all* image header WCS keywords to provide a default value for all image arrays in a binary table (n.b. not pixel list). This default may be overridden by the column-specific form of the keyword.

     For example, a keyword like CRPIXja would apply to all image arrays in a binary table with alternate representation "a" unless overridden by jCRPna.

     Specifically the keywords are those listed above for WCSHDR_AUXIMG plus

     ---

     WCSAXESa

     for WCAXna

     ---

     which defines the coordinate dimensionality, and the following keywords which are parameterized by axis number:

     ---

     CRPIXja	for jCRPna
     PCi_ja	for ijPCna
     CDi_ja	for ijCDna
     CDELTia	for iCDEna
     CROTAi	for iCROTn
     CROTAia		... Only if WCSHDR_CROTAia is set.
     CUNITia	for iCUNna
     CTYPEia	for iCTYna
     CRVALia	for iCRVna
     PVi_ma	for iVn_ma
     PSi_ma	for iSn_ma

     ---

     ---

     CNAMEia	for iCNAna
     CRDERia	for iCRDna
     CSYERia	for iCSYna

     ---

     where the image-header keywords on the left provide default values for the column specific keywords on the right.

     This full inheritance mechanism only applies to binary table image arrays, not pixel lists, because in the latter case there is no well-defined association between coordinate axis number and column number.

     Note that CNAMEia, CRDERia, CSYERia, and their variants are not used by WCSLIB but are stored in the wcsprm struct as auxiliary information.

     Note especially that at least one wcsprm struct will be returned for each "a" found in one of the image header keywords listed above:

     • If the image header keywords for "a" are not inherited by a binary table, then the struct will not be associated with any particular table column number and it is up to the user to provide an association.

     • If the image header keywords for "a" are inherited by a binary table image array, then those keywords are considered to be "exhausted" and do not result in a separate wcsprm struct.

   For example, to accept CD00i00j and PC00i00j and reject all other extensions, use

   relax = WCSHDR_reject | WCSHDR_CD00i00j | WCSHDR_PC00i00j;

   The parser always treats EPOCH as subordinate to EQUINOXa if both are present, and VSOURCEa is always subordinate to ZSOURCEa.

   Likewise, VELREF is subordinate to the formalism of WCS Paper III, see spcaips().

   Neither wcspih() nor wcsbth() currently recognize the AIPS-convention keywords ALTRPIX or ALTRVAL which effectively define an alternative representation for a spectral axis.

6. Depending on what flags have been set in its relax argument, wcsbth() could return as many as 27027 wcsprm structs:

   • Up to 27 unattached representations derived from image header keywords.

   • Up to 27 structs for each of up to 999 columns containing an image arrays.

   • Up to 27 structs for a pixel list.

   Note that it is considered legitimate for a column to contain an image array and also form part of a pixel list, and in particular that wcsbth() does not check the TFORM keyword for a pixel list column to check that it is scalar.

   In practice, of course, a realistic binary table header is unlikely to contain more than a handful of images.

   In order for wcsbth() to create a wcsprm struct for a particular coordinate representation, at least one WCS keyword that defines an axis number must be present, either directly or by inheritance if WCSHDR_ALLIMG is set.

   When the image header keywords for an alternate representation are inherited by a binary table image array via WCSHDR_ALLIMG, those keywords are considered to be "exhausted" and do not result in a separate wcsprm struct. Otherwise they do.

7. Neither wcspih() nor wcsbth() check for duplicated keywords, in most cases they accept the last encountered.

8. wcspih() and wcsbth() use wcsnpv() and wcsnps() (refer to the prologue of wcs.h) to match the size of the pv[] and ps[] arrays in the wcsprm structs to the number in the header. Consequently there are no unused elements in the pv[] and ps[] arrays, indeed they will often be of zero length.

9. The FITS WCS standard for pixel lists assumes that a pixel list defines one and only one image, i.e. that each row of the binary table refers to just one event, e.g. the detection of a single photon or neutrino.

   In the absence of a formal mechanism for identifying the columns containing pixel coordinates (as opposed to pixel values or ancillary data recorded at the time the photon or neutrino was detected), Paper I discusses how the WCS keywords themselves may be used to identify them.

   In practice, however, pixel lists have been used to store multiple images. Besides not specifying how to identify columns, the pixel list convention is also silent on the method to be used to associate table columns with image axes.

   wcsbth() simply collects all WCS keywords for a particular coordinate representation (i.e. the "a" value in TCTYna) into one wcsprm struct. However, these alternates need not be associated with the same table columns and this allows a pixel list to contain up to 27 separate images. As usual, if one of these representations happened to contain more than two celestial axes, for example, then an error would result when wcsset() is invoked on it. In this case the "colsel" argument could be used to restrict the columns used to construct the representation so that it only contained one pair of celestial axes.

int wcstab

(

struct wcsprm *

wcs)

wcstab() assists in filling in the information in the wcsprm struct relating to coordinate lookup tables.

Tabular coordinates ('TAB') present certain difficulties in that the main components of the lookup table - the multidimensional coordinate array plus an index vector for each dimension - are stored in a FITS binary table extension (BINTABLE). Information required to locate these arrays is stored in PVi_ma and PSi_ma keywords in the image header.

wcstab() parses the PVi_ma and PSi_ma keywords associated with each 'TAB' axis and allocates memory in the wcsprm struct for the required number of tabprm structs. It sets as much of the tabprm struct as can be gleaned from the image header, and also sets up an array of wtbarr structs (described in the prologue of wcs.h) to assist in extracting the required arrays from the BINTABLE extension(s).

It is then up to the user to allocate memory for, and copy arrays from the BINTABLE extension(s) into the tabprm structs. A CFITSIO routine, fits_read_wcstab(), has been provided for this purpose, see getwcstab.h. wcsset() will automatically take control of this allocated memory, in particular causing it to be free'd by wcsfree(); the user must not attempt to free it after wcsset() has been called.

Note that wcspih() and wcsbth() automatically invoke wcstab() on each of the wcsprm structs that they return.

Parameters

[in,out]

wcs

Coordinate transformation parameters (see below). wcstab() sets ntab, tab, nwtb and wtb, allocating memory for the tab and wtb arrays. This allocated memory will be free'd automatically by wcsfree().

Returns

Status return value:

• 0: Success.
• 1: Null wcsprm pointer passed.
• 2: Memory allocation failed.
• 3: Invalid tabular parameters.

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

int wcsidx	(	int	nwcs,
		struct wcsprm **	wcs,
		int	alts[27]
	)

wcsidx() returns an array of 27 indices for the alternate coordinate representations in the array of wcsprm structs returned by wcspih(). For the array returned by wcsbth() it returns indices for the unattached (colnum == 0) representations derived from image header keywords - use wcsbdx() for those derived from binary table image arrays or pixel lists keywords.

Parameters

[in]	nwcs	Number of coordinate representations in the array.
[in]	wcs	Pointer to an array of wcsprm structs returned by wcspih() or wcsbth().
[out]	alts	Index of each alternate coordinate representation in the array: alts[0] for the primary, alts[1] for 'A', etc., set to -1 if not present. For example, if there was no 'P' representation then alts['P'-'A'+1] == -1; Otherwise, the address of its wcsprm struct would be wcs + alts['P'-'A'+1];

Returns

Status return value:

• 0: Success.
• 1: Null wcsprm pointer passed.

int wcsbdx	(	int	nwcs,
		struct wcsprm **	wcs,
		int	type,
		short	alts[1000][28]
	)

wcsbdx() returns an array of 999 x 27 indices for the alternate coordinate representions for binary table image arrays xor pixel lists in the array of wcsprm structs returned by wcsbth(). Use wcsidx() for the unattached representations derived from image header keywords.

Parameters

[in]	nwcs	Number of coordinate representations in the array.
[in]	wcs	Pointer to an array of wcsprm structs returned by wcsbth().
[in]	type	Select the type of coordinate representation: 0: binary table image arrays, 1: pixel lists.
[out]	alts	Index of each alternate coordinate represention in the array: alts[col][0] for the primary, alts[col][1] for 'A', to alts[col][26] for 'Z', where col is the 1-relative column number, and col == 0 is used for unattached image headers. Set to -1 if not present. alts[col][27] counts the number of coordinate representations of the chosen type for each column. For example, if there was no 'P' represention for column 13 then alts[13]['P'-'A'+1] == -1; Otherwise, the address of its wcsprm struct would be wcs + alts[13]['P'-'A'+1];

Returns

Status return value:

• 0: Success.
• 1: Null wcsprm pointer passed.

int wcsvfree	(	int *	nwcs,
		struct wcsprm **	wcs
	)

wcsvfree() frees the memory allocated by wcspih() or wcsbth() for the array of wcsprm structs, first invoking wcsfree() on each of the array members.

Parameters

[in,out]	nwcs	Number of coordinate representations found; set to 0 on return.
[in,out]	wcs	Pointer to the array of wcsprm structs; set to 0 on return.

Returns

Status return value:

• 0: Success.
• 1: Null wcsprm pointer passed.

int wcshdo	(	int	relax,
		struct wcsprm *	wcs,
		int *	nkeyrec,
		char **	header
	)

wcshdo() translates a wcsprm struct into a FITS header. If the colnum member of the struct is non-zero then a binary table image array header will be produced. Otherwise, if the colax[] member of the struct is set non-zero then a pixel list header will be produced. Otherwise, a primary image or image extension header will be produced.

If the struct was originally constructed from a header, e.g. by wcspih(), the output header will almost certainly differ in a number of respects:

• The output header only contains WCS-related keywords. In particular, it does not contain syntactically-required keywords such as SIMPLE, NAXIS, BITPIX, or END.
• Deprecated (e.g. CROTAn) or non-standard usage will be translated to standard (this is partially dependent on whether wcsfix() was applied).
• Quantities will be converted to the units used internally, basically SI with the addition of degrees.
• Floating-point quantities may be given to a different decimal precision.
• Elements of the PCi_ja matrix will be written if and only if they differ from the unit matrix. Thus, if the matrix is unity then no elements will be written.
• Additional keywords such as WCSAXESa, CUNITia, LONPOLEa and LATPOLEa may appear.
• The original keycomments will be lost, although wcshdo() tries hard to write meaningful comments.
• Keyword order may be changed.

Keywords can be translated between the image array, binary table, and pixel lists forms by manipulating the colnum or colax[] members of the wcsprm struct.

Parameters

[in]	relax	Degree of permissiveness: 0: Recognize only FITS keywords defined by the published WCS standard. -1: Admit all informal extensions of the WCS standard. Fine-grained control of the degree of permissiveness is also possible as explained in the notes below.
[in,out]	wcs	Pointer to a wcsprm struct containing coordinate transformation parameters. Will be initialized if necessary.
[out]	nkeyrec	Number of FITS header keyrecords returned in the "header" array.
[out]	header	Pointer to an array of char holding the header. Storage for the array is allocated by wcshdo() in blocks of 2880 bytes (32 x 80-character keyrecords) and must be free'd by the user to avoid memory leaks. Each keyrecord is 80 characters long and is *NOT* null-terminated, so the first keyrecord starts at (*header)[0], the second at (*header)[80], etc.

Returns

Status return value (associated with wcs_errmsg[]):

• 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().

Notes:
wcshdo() interprets the relax argument as a vector of flag bits to provide fine-grained control over what non-standard WCS keywords to write. The flag bits are subject to change in future and should be set by using the preprocessor macros (see below) for the purpose.

• WCSHDO_none: Don't use any extensions.

• WCSHDO_all: Write all recognized extensions, equivalent to setting each flag bit.

• WCSHDO_safe: Write all extensions that are considered to be safe and recommended.

• WCSHDO_DOBSn: Write DOBSn, the column-specific analogue of DATE-OBS for use in binary tables and pixel lists. WCS Paper III introduced DATE-AVG and DAVGn but by an oversight DOBSn (the obvious analogy) was never formally defined by the standard. The alternative to using DOBSn is to write DATE-OBS which applies to the whole table. This usage is considered to be safe and is recommended.

• WCSHDO_TPCn_ka: WCS Paper I defined

  • TPn_ka and TCn_ka for pixel lists

  but WCS Paper II uses TPCn_ka in one example and subsequently the errata for the WCS papers legitimized the use of

  • TPCn_ka and TCDn_ka for pixel lists

  provided that the keyword does not exceed eight characters. This usage is considered to be safe and is recommended because of the non-mnemonic terseness of the shorter forms.

• WCSHDO_PVn_ma: WCS Paper I defined

  • iVn_ma and iSn_ma for bintables and
  • TVn_ma and TSn_ma for pixel lists

  but WCS Paper II uses iPVn_ma and TPVn_ma in the examples and subsequently the errata for the WCS papers legitimized the use of

  • iPVn_ma and iPSn_ma for bintables and
  • TPVn_ma and TPSn_ma for pixel lists

  provided that the keyword does not exceed eight characters. This usage is considered to be safe and is recommended because of the non-mnemonic terseness of the shorter forms.

• WCSHDO_CRPXna: For historical reasons WCS Paper I defined

  • jCRPXn, iCDLTn, iCUNIn, iCTYPn, and iCRVLn for bintables and
  • TCRPXn, TCDLTn, TCUNIn, TCTYPn, and TCRVLn for pixel lists

  for use without an alternate version specifier. However, because of the eight-character keyword constraint, in order to accommodate column numbers greater than 99 WCS Paper I also defined

  • jCRPna, iCDEna, iCUNna, iCTYna and iCRVna for bintables and
  • TCRPna, TCDEna, TCUNna, TCTYna and TCRVna for pixel lists

  for use with an alternate version specifier (the "a"). Like the PC, CD, PV, and PS keywords there is an obvious tendency to confuse these two forms for column numbers up to 99. It is very unlikely that any parser would reject keywords in the first set with a non-blank alternate version specifier so this usage is considered to be safe and is recommended.

• WCSHDO_CNAMna: WCS Papers I and III defined

  • iCNAna, iCRDna, and iCSYna for bintables and
  • TCNAna, TCRDna, and TCSYna for pixel lists

  By analogy with the above, the long forms would be

  • iCNAMna, iCRDEna, and iCSYEna for bintables and
  • TCNAMna, TCRDEna, and TCSYEna for pixel lists

  Note that these keywords provide auxiliary information only, none of them are needed to compute world coordinates. This usage is potentially unsafe and is not recommended at this time.

• WCSHDO_WCSNna: In light of wcsbth() note 4, write WCSNna instead of TWCSna for pixel lists. While wcsbth() treats WCSNna and TWCSna as equivalent, other parsers may not. Consequently, this usage is potentially unsafe and is not recommended at this time.

Variable Documentation

const char * wcshdr_errmsg[]

Error messages to match the status value returned from each function. Use wcs_errmsg[] for status returns from wcshdo().