WCSLIB: wcshdr.h File Reference

WCSLIB 8.9

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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.
#define | WCSHDR_all 0x000FFFFF
| Bit mask for wcspih() and wcsbth() - accept all extensions.
#define | WCSHDR_reject 0x10000000
| Bit mask for wcspih() and wcsbth() - reject non-standard keywords.
#define | WCSHDR_strict 0x20000000
#define | WCSHDR_CROTAia 0x00000001
| Bit mask for wcspih() and wcsbth() - accept CROTAia, iCROTna, TCROTna.
#define | WCSHDR_VELREFa 0x00000002
| Bit mask for wcspih() and wcsbth() - accept VELREFa.
#define | WCSHDR_CD00i00j 0x00000004
| Bit mask for wcspih() and wcsbth() - accept CD00i00j.
#define | WCSHDR_PC00i00j 0x00000008
| Bit mask for wcspih() and wcsbth() - accept PC00i00j.
#define | WCSHDR_PROJPn 0x00000010
| Bit mask for wcspih() and wcsbth() - accept PROJPn.
#define | WCSHDR_CD0i_0ja 0x00000020
#define | WCSHDR_PC0i_0ja 0x00000040
#define | WCSHDR_PV0i_0ma 0x00000080
#define | WCSHDR_PS0i_0ma 0x00000100
#define | WCSHDR_DOBSn 0x00000200
| Bit mask for wcspih() and wcsbth() - accept DOBSn.
#define | WCSHDR_OBSGLBHn 0x00000400
#define | WCSHDR_RADECSYS 0x00000800
| Bit mask for wcspih() and wcsbth() - accept RADECSYS.
#define | WCSHDR_EPOCHa 0x00001000
| Bit mask for wcspih() and wcsbth() - accept EPOCHa.
#define | WCSHDR_VSOURCE 0x00002000
| Bit mask for wcspih() and wcsbth() - accept VSOURCEa.
#define | WCSHDR_DATEREF 0x00004000
#define | WCSHDR_LONGKEY 0x00008000
| Bit mask for wcspih() and wcsbth() - accept long forms of the alternate binary table and pixel list WCS keywords.
#define | WCSHDR_CNAMn 0x00010000
| Bit mask for wcspih() and wcsbth() - accept iCNAMn, TCNAMn, iCRDEn, TCRDEn, iCSYEn, TCSYEn.
#define | WCSHDR_AUXIMG 0x00020000
| Bit mask for wcspih() and wcsbth() - allow the image-header form of an auxiliary WCS keyword to provide a default value for all images.
#define | WCSHDR_ALLIMG 0x00040000
| 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.
#define | WCSHDR_IMGHEAD 0x00100000
| Bit mask for wcsbth() - restrict to image header keywords only.
#define | WCSHDR_BIMGARR 0x00200000
| Bit mask for wcsbth() - restrict to binary table image array keywords only.
#define | WCSHDR_PIXLIST 0x00400000
| Bit mask for wcsbth() - restrict to pixel list keywords only.
#define | WCSHDO_none 0x00000
| Bit mask for wcshdo() - don't write any extensions.
#define | WCSHDO_all 0x000FF
| Bit mask for wcshdo() - write all extensions.
#define | WCSHDO_safe 0x0000F
| Bit mask for wcshdo() - write safe extensions only.
#define | WCSHDO_DOBSn 0x00001
| Bit mask for wcshdo() - write DOBSn.
#define | WCSHDO_TPCn_ka 0x00002
| Bit mask for wcshdo() - write TPCn_ka.
#define | WCSHDO_PVn_ma 0x00004
| Bit mask for wcshdo() - write iPVn_ma, TPVn_ma, iPSn_ma, TPSn_ma.
#define | WCSHDO_CRPXna 0x00008
| Bit mask for wcshdo() - write jCRPXna, TCRPXna, iCDLTna, TCDLTna, iCUNIna, TCUNIna, iCTYPna, TCTYPna, iCRVLna, TCRVLna.
#define | WCSHDO_CNAMna 0x00010
| Bit mask for wcshdo() - write iCNAMna, TCNAMna, iCRDEna, TCRDEna, iCSYEna, TCSYEna.
#define | WCSHDO_WCSNna 0x00020
| Bit mask for wcshdo() - write WCSNna instead of TWCSna.
#define | WCSHDO_P12 0x01000
#define | WCSHDO_P13 0x02000
#define | WCSHDO_P14 0x04000
#define | WCSHDO_P15 0x08000
#define | WCSHDO_P16 0x10000
#define | WCSHDO_P17 0x20000
#define | WCSHDO_EFMT 0x40000

## 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.
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.
int | wcstab (struct wcsprm *wcs)
| Tabular construction routine.
int | wcsidx (int nwcs, struct wcsprm **wcs, int alts[27])
| Index alternate coordinate representations.
int | wcsbdx (int nwcs, struct wcsprm **wcs, int type, short alts[1000][28])
| Index alternate coordinate representions.
int | wcsvfree (int *nwcs, struct wcsprm **wcs)
| Free the array of wcsprm structs.
int | wcshdo (int ctrl, struct wcsprm *wcs, int *nkeyrec, char **header)
| Write out a wcsprm struct as a FITS header.

## Variables
const char * | wcshdr_errmsg []
| Status return messages.

## Detailed Description

Routines in this suite are aimed at extracting WCS information from a FITS file. The information is encoded via keywords defined in

"Representations of world coordinates in FITS",
Greisen, E.W., & Calabretta, M.R. 2002, A&A, 395, 1061 (WCS Paper I)
"Representations of celestial coordinates in FITS",
Calabretta, M.R., & Greisen, E.W. 2002, A&A, 395, 1077 (WCS Paper II)
"Representations of spectral coordinates in FITS",
Greisen, E.W., Calabretta, M.R., Valdes, F.G., & Allen, S.L.
2006, A&A, 446, 747 (WCS Paper III)
"Representations of distortions in FITS world coordinate systems",
Calabretta, M.R. et al. (WCS Paper IV, draft dated 2004/04/22),
available from http://www.atnf.csiro.au/computing/software/wcs
"Representations of time coordinates in FITS -
Time and relative dimension in space",
Rots, A.H., Bunclark, P.S., Calabretta, M.R., Allen, S.L.,
Manchester, R.N., & Thompson, W.T. 2015, A&A, 574, A36 (WCS Paper VII)

These routines 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 freed 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

## ◆ WCSHDR_none

#define WCSHDR_none 0x00000000

Bit mask for wcspih() and wcsbth() - reject all extensions.

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

Refer to wcsbth() note 5.

## ◆ WCSHDR_all

#define WCSHDR_all 0x000FFFFF

Bit mask for wcspih() and wcsbth() - accept all extensions.

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

Refer to wcsbth() note 5.

## ◆ WCSHDR_reject

#define WCSHDR_reject 0x10000000

Bit mask for wcspih() and wcsbth() - reject non-standard keywords.

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

Refer to wcsbth() note 5.

## ◆ WCSHDR_strict

#define WCSHDR_strict 0x20000000

## ◆ WCSHDR_CROTAia

#define WCSHDR_CROTAia 0x00000001

Bit mask for wcspih() and wcsbth() - accept CROTAia, iCROTna, TCROTna.

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

Refer to wcsbth() note 5.

## ◆ WCSHDR_VELREFa

#define WCSHDR_VELREFa 0x00000002

Bit mask for wcspih() and wcsbth() - accept VELREFa.

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

Refer to wcsbth() note 5.

## ◆ WCSHDR_CD00i00j

#define WCSHDR_CD00i00j 0x00000004

Bit mask for wcspih() and wcsbth() - accept CD00i00j.

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

Refer to wcsbth() note 5.

## ◆ WCSHDR_PC00i00j

#define WCSHDR_PC00i00j 0x00000008

Bit mask for wcspih() and wcsbth() - accept PC00i00j.

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

Refer to wcsbth() note 5.

## ◆ WCSHDR_PROJPn

#define WCSHDR_PROJPn 0x00000010

Bit mask for wcspih() and wcsbth() - accept PROJPn.

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

Refer to wcsbth() note 5.

## ◆ WCSHDR_CD0i_0ja

#define WCSHDR_CD0i_0ja 0x00000020

## ◆ WCSHDR_PC0i_0ja

#define WCSHDR_PC0i_0ja 0x00000040

## ◆ WCSHDR_PV0i_0ma

#define WCSHDR_PV0i_0ma 0x00000080

## ◆ WCSHDR_PS0i_0ma

#define WCSHDR_PS0i_0ma 0x00000100

## ◆ WCSHDR_DOBSn

#define WCSHDR_DOBSn 0x00000200

Bit mask for wcspih() and wcsbth() - accept DOBSn.

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

Refer to wcsbth() note 5.

## ◆ WCSHDR_OBSGLBHn

#define WCSHDR_OBSGLBHn 0x00000400

## ◆ WCSHDR_RADECSYS

#define WCSHDR_RADECSYS 0x00000800

Bit mask for wcspih() and wcsbth() - accept RADECSYS.

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

Refer to wcsbth() note 5.

## ◆ WCSHDR_EPOCHa

#define WCSHDR_EPOCHa 0x00001000

Bit mask for wcspih() and wcsbth() - accept EPOCHa.

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

Refer to wcsbth() note 5.

## ◆ WCSHDR_VSOURCE

#define WCSHDR_VSOURCE 0x00002000

Bit mask for wcspih() and wcsbth() - accept VSOURCEa.

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

Refer to wcsbth() note 5.

## ◆ WCSHDR_DATEREF

#define WCSHDR_DATEREF 0x00004000

## ◆ WCSHDR_LONGKEY

#define WCSHDR_LONGKEY 0x00008000

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

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.

## ◆ WCSHDR_CNAMn

#define WCSHDR_CNAMn 0x00010000

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

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

Refer to wcsbth() note 5.

## ◆ WCSHDR_AUXIMG

#define WCSHDR_AUXIMG 0x00020000

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

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.

## ◆ WCSHDR_ALLIMG

#define WCSHDR_ALLIMG 0x00040000

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.

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.

## ◆ WCSHDR_IMGHEAD

#define WCSHDR_IMGHEAD 0x00100000

Bit mask for wcsbth() - restrict to image header keywords only.

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

## ◆ WCSHDR_BIMGARR

#define WCSHDR_BIMGARR 0x00200000

Bit mask for wcsbth() - restrict to binary table image array keywords only.

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

## ◆ WCSHDR_PIXLIST

#define WCSHDR_PIXLIST 0x00400000

Bit mask for wcsbth() - restrict to pixel list keywords only.

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

## ◆ WCSHDO_none

#define WCSHDO_none 0x00000

Bit mask for wcshdo() - don't write any extensions.

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

Refer to the notes for wcshdo().

## ◆ WCSHDO_all

#define WCSHDO_all 0x000FF

Bit mask for wcshdo() - write all extensions.

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

Refer to the notes for wcshdo().

## ◆ WCSHDO_safe

#define WCSHDO_safe 0x0000F

Bit mask for wcshdo() - write safe extensions only.

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

Refer to the notes for wcshdo().

## ◆ WCSHDO_DOBSn

#define WCSHDO_DOBSn 0x00001

Bit mask for wcshdo() - write DOBSn.

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().

## ◆ WCSHDO_TPCn_ka

#define WCSHDO_TPCn_ka 0x00002

Bit mask for wcshdo() - write TPCn_ka.

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().

## ◆ WCSHDO_PVn_ma

#define WCSHDO_PVn_ma 0x00004

Bit mask for wcshdo() - write iPVn_ma, TPVn_ma, iPSn_ma, TPSn_ma.

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().

## ◆ WCSHDO_CRPXna

#define WCSHDO_CRPXna 0x00008

Bit mask for wcshdo() - write jCRPXna, TCRPXna, iCDLTna, TCDLTna, iCUNIna, TCUNIna, iCTYPna, TCTYPna, iCRVLna, TCRVLna.

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().

## ◆ WCSHDO_CNAMna

#define WCSHDO_CNAMna 0x00010

Bit mask for wcshdo() - write iCNAMna, TCNAMna, iCRDEna, TCRDEna, iCSYEna, TCSYEna.

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().

## ◆ WCSHDO_WCSNna

#define WCSHDO_WCSNna 0x00020

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

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

Refer to the notes for wcshdo().

## ◆ WCSHDO_P12

#define WCSHDO_P12 0x01000

## ◆ WCSHDO_P13

#define WCSHDO_P13 0x02000

## ◆ WCSHDO_P14

#define WCSHDO_P14 0x04000

## ◆ WCSHDO_P15

#define WCSHDO_P15 0x08000

## ◆ WCSHDO_P16

#define WCSHDO_P16 0x10000

## ◆ WCSHDO_P17

#define WCSHDO_P17 0x20000

## ◆ WCSHDO_EFMT

#define WCSHDO_EFMT 0x40000

## Enumeration Type Documentation

## ◆ wcshdr_errmsg_enum

enum wcshdr_errmsg_enum

Enumerator
WCSHDRERR_SUCCESS |
WCSHDRERR_NULL_POINTER |
WCSHDRERR_MEMORY |
WCSHDRERR_BAD_COLUMN |
WCSHDRERR_PARSER |
WCSHDRERR_BAD_TABULAR_PARAMS |

## Function Documentation

## ◆ wcspih()

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

FITS WCS parser routine for image headers.

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, III, IV, and VII 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. wcspih() also handles keywords associated with non-standard distortion functions described in the prologue of dis.h.

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, although it cannot handle keywords relating to distortion functions, which may only exist in an image header (primary or extension).

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. 4: As above, but also report the accepted WCS keyrecords, with a summary of the number accepted as well as rejected. 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: As above, but 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 global WCS-related keywords such as '{DATE,MJD}-{OBS,BEG,AVG,END}' and the other basic time-related keywords, and 'OBSGEO-{X,Y,Z,L,B,H}'. 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:

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

## ◆ wcsbth()

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.

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, III, and VII 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. 4: As above, but also report the accepted WCS keyrecords, with a summary of the number accepted as well as rejected. 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 global WCS-related keywords such as '{DATE,MJD}-{OBS,BEG,AVG,END}' and the other basic time-related keywords, and 'OBSGEO-{X,Y,Z,L,B,H}'. 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, III, and VII that are not parameterized 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 keyrecords (that are not otherwise explicitly accepted by one of the flags below). 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. It is mainly intended for testing conformance of a FITS header to the WCS standard.

     Keyrecords may be non-standard in several ways:

     - The keyword may be syntactically valid but with keyvalue of incorrect type or invalid syntax, or the keycomment may be malformed.

     - The keyword may strongly resemble a WCS keyword but not, in fact, be one because it does not conform to the standard. For example, "CRPIX01" looks like a CRPIXja keyword, but in fact the leading zero on the axis number violates the basic FITS standard. Likewise, "LONPOLE2" is not a valid LONPOLEa keyword in the WCS standard, and indeed there is nothing the parser can sensibly do with it.

     - Use of the keyword may be deprecated by the standard. Such will be rejected if not explicitly accepted via one of the flags below.

   - WCSHDR_strict: As for WCSHDR_reject, but also reject AIPS-convention keywords and all other deprecated usage that is not explicitly accepted.

   - WCSHDR_CROTAia: Accept CROTAia (wcspih()), iCROTna (wcsbth()), TCROTna (wcsbth()).

   - 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_CD0i_0ja: Accept CD0i_0ja (wcspih()).
   - WCSHDR_PC0i_0ja: Accept PC0i_0ja (wcspih()).
   - WCSHDR_PV0i_0ma: Accept PV0i_0ja (wcspih()).

   - WCSHDR_PS0i_0ma: Accept PS0i_0ja (wcspih()). Allow the numerical index to have a leading zero in doubly- parameterized keywords, for example, PC01_01. WCS Paper I (Sects 2.1.2 & 2.1.4) explicitly disallows leading zeroes. The FITS 3.0 standard document (Sect. 4.1.2.1) states that the index in singly-parameterized keywords (e.g. CTYPEia) "shall not have leading zeroes", and later in Sect. 8.1 that "leading zeroes must not be used" on PVi_ma and PSi_ma. However, by an oversight, it is silent on PCi_ja and CDi_ja.

   - 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_OBSGLBHn (wcsbth() only): Allow OBSGLn, OBSGBn, and OBSGHn, the column-specific analogues of OBSGEO-L, OBSGEO-B, and OBSGEO-H. By an oversight these were never formally defined in the standard.

   - 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_EPOCHa: Accept EPOCHa.

   - 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_DATEREF: Accept DATE-REF, MJD-REF, MJD-REFI, MJD-REFF, JDREF, JD-REFI, and JD-REFF as synonyms for the standard keywords, DATEREF, MJDREF, MJDREFI, MJDREFF, JDREF, JDREFI, and JDREFF. The latter buck the pattern set by the other date keywords ({DATE,MJD}-{OBS,BEG,AVG,END}), thereby increasing the potential for confusion and error.

   - 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
     TCZPHna | TCZPHna | : | — | TCZPna | — | TCZPna | CZPHSia
     iCPERna | TCPERna | : | — | iCPRna | — | TCPRna | CPERIia

     Note that CNAMEia, CRDERia, CSYERia, CZPHSia, CPERIia, 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, TCZPHn, iCPERn, TCNAMn, TCRDEn, TCSYEn, TCZPHn, and TCPERn, 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:

     LONPOLEa | for LONPna
     LATPOLEa | for LATPna
     VELREF |  | ... (No column-specific form.)
     VELREFa |  | ... Only if WCSHDR_VELREFa is set.

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

     WCSNAMEa | for WCSNna | ... Or TWCSna (see below).
     DATE-OBS | for DOBSn
     MJD-OBS | for MJDOBn
     RADESYSa | for RADEna
     RADECSYS | for RADEna | ... Only if WCSHDR_RADECSYS is set.
     EPOCH |  | ... (No column-specific form.)
     EPOCHa |  | ... Only if WCSHDR_EPOCHa is set.
     EQUINOXa | for EQUIna

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

     Note that, according to Sect. 8.1 of WCS Paper III, and Sect. 5.2 of WCS Paper VII, the following are always inherited:

     RESTFREQ | for RFRQna
     RESTFRQa | for RFRQna
     RESTWAVa | for RWAVna

     being those actually used by WCSLIB, together with the following auxiliary keywords, many of which do not have binary table equivalents and therefore can only be inherited:

     TIMESYS |
     TREFPOS | for MJDAn
     TREFDIR | for MJDAn
     PLEPHEM |
     TIMEUNIT |
     DATEREF |
     MJDREF |
     MJDREFI |
     MJDREFF |
     JDREF |
     JDREFI |
     JDREFF |
     TIMEOFFS |
     DATE-BEG |
     DATE-AVG | for DAVGn
     DATE-END |
     MJD-BEG |
     MJD-AVG | for MJDAn
     MJD-END |
     JEPOCH |
     BEPOCH |
     TSTART |
     TSTOP |
     XPOSURE |
     TELAPSE |
     TIMSYER |
     TIMRDER |
     TIMEDEL |
     TIMEPIXR |
     OBSGEO-X | for OBSGXn
     OBSGEO-Y | for OBSGYn
     OBSGEO-Z | for OBSGZn
     OBSGEO-L | for OBSGLn
     OBSGEO-B | for OBSGBn
     OBSGEO-H | for OBSGHn
     OBSORBIT |
     SPECSYSa | for SPECna
     SSYSOBSa | for SOBSna
     VELOSYSa | for VSYSna
     VSOURCEa | for VSOUna | ... Only if WCSHDR_VSOURCE is set.
     ZSOURCEa | for ZSOUna
     SSYSSRCa | for SSRCna
     VELANGLa | for VANGna

     Global image-header keywords, such as MJD-OBS, apply to all alternate representations, and would therefore 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 one potential difficulty in using WCSHDR_AUXIMG is that of erroneously inheriting one of these four keywords.

     Also, beware of potential inconsistencies that may arise where, for example, DATE-OBS is inherited, but MJD-OBS is overridden by MJDOBn and specifies a different time. Pairs in this category are:

     DATE-OBS/DOBSn versus MJD-OBS/MJDOBn
     DATE-AVG/DAVGn versus MJD-AVG/MJDAn
     RESTFRQa/RFRQna versus RESTWAVa/RWAVna
     OBSGEO-[XYZ]/OBSG[XYZ]n versus OBSGEO-[LBH]/OBSG[LBH]n

     The wcsfixi() routines datfix() and obsfix() are provided to check the consistency of these and other such pairs of 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 that are parameterized by axis number, such as CTYPEia.

   - 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 that 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
     CZPHSia | for TCZPna
     CPERIia | for iCPRna

     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 (see note 9 below).

     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;
   WCSHDR_PC00i00j
   #define WCSHDR_PC00i00j
   Bit mask for wcspih() and wcsbth() - accept PC00i00j.
   Definition wcshdr.h:1293
   WCSHDR_CD00i00j
   #define WCSHDR_CD00i00j
   Bit mask for wcspih() and wcsbth() - accept CD00i00j.
   Definition wcshdr.h:1292
   WCSHDR_reject
   #define WCSHDR_reject
   Bit mask for wcspih() and wcsbth() - reject non-standard keywords.
   Definition wcshdr.h:1287

   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, for which the device "pixel" coordinates are stored in separate scalar columns of the table.

   In the absence of a standard for pixel lists - or even an informal description! - let alone a formal mechanism for identifying the columns containing pixel coordinates (as opposed to pixel values or metadata recorded at the time the photon or neutrino was detected), WCS 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.

   An additional shortcoming is the absence of a formal method for associating global binary-table WCS keywords, such as WCSNna or MJDOBn, with a pixel list image, whether one or several.

   In light of these uncertainties, wcsbth() simply collects all WCS keywords for a particular pixel list 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.

   Global, binary-table WCS keywords are considered to apply to the pixel list image with matching alternate (e.g. the "a" value in LONPna or EQUIna), regardless of the table columns the image occupies. In other words, the column number is ignored (the "n" value in LONPna or EQUIna). This also applies for global, binary-table WCS keywords that have no alternates, such as MJDOBn and OBSGXn, which match all images in a pixel list. Take heed that this may lead to counterintuitive behaviour, especially where such a keyword references a column that does not store pixel coordinates, and moreso where the pixel list stores only a single image. In fact, as the column number, n, is ignored for such keywords, it would make no difference even if they referenced non-existent columns. Moreover, there is no requirement for consistency in the column numbers used for such keywords, even for OBSGXn, OBSGYn, and OBSGZn which are meant to define the elements of a coordinate vector. Although it would surely be perverse to construct a pixel list like this, such a situation may still arise in practice where columns are deleted from a binary table.

   The situation with global, binary-table WCS keywords becomes potentially even more confusing when image arrays and pixel list images coexist in one binary table. In that case, a keyword such as MJDOBn may legitimately appear multiple times with n referencing different image arrays. Which then is the one that applies to the pixel list images? In this implementation, it is the last instance that appears in the header, whether or not it is also associated with an image array.

## ◆ wcstab()

int wcstab | ( | struct wcsprm * | wcs | ) |

Tabular construction routine.

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 wtbarr.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 freed 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 freed 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().

## ◆ wcsidx()

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

Index alternate coordinate representations.

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.

## ◆ wcsbdx()

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

Index alternate coordinate representions.

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.

## ◆ wcsvfree()

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

Free the array of wcsprm structs.

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 0x0 on return.

Returns
  Status return value:
  - 0: Success.
  - 1: Null wcsprm pointer passed.

## ◆ wcshdo()

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

Write out a wcsprm struct as a FITS 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.
- 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.
- The redundant keywords MJDREF, JDREF, JDREFI, JDREFF, all of which duplicate MJDREFI + MJDREFF, are never written. OBSGEO-[LBH] are not written if OBSGEO-[XYZ] are defined.
- Deprecated (e.g. CROTAn, RESTFREQ, VELREF, RADECSYS, EPOCH, VSOURCEa) or non-standard usage will be translated to standard (this is partially dependent on whether wcsfix() was applied).
- Additional keywords such as WCSAXESa, CUNITia, LONPOLEa and LATPOLEa may appear.
- 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.
- The original keycomments will be lost, although wcshdo() tries hard to write meaningful comments.
- Keyword order will almost certainly 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] | ctrl | Vector of flag bits that controls the degree of permissiveness in departing from the published WCS standard, and also controls the formatting of floating-point keyvalues. Set it to zero to get the default behaviour. Flag bits for the degree of permissiveness: WCSHDO_none: Recognize only FITS keywords defined by the published WCS standard. WCSHDO_all: Admit all recognized informal extensions of the WCS standard. Fine-grained control of the degree of permissiveness is also possible as explained in the notes below. As for controlling floating-point formatting, by default wcshdo() uses "%20.12G" for non-parameterized keywords such as LONPOLEa, and attempts to make the header more human-readable by using the same "f" format for all values of each of the following parameterized keywords: CRPIXja, PCi_ja, and CDELTia (n.b. excluding CRVALia). Each has the same field width and precision so that the decimal points line up. The precision, allowing for up to 15 significant digits, is chosen so that there are no excess trailing zeroes. A similar formatting scheme applies by default for distortion function parameters. However, where the values of, for example, CDELTia differ by many orders of magnitude, the default formatting scheme may cause unacceptable loss of precision for the lower-valued keyvalues. Thus the default behaviour may be overridden: WCSHDO_P12: Use "%20.12G" format for all floating- point keyvalues (12 significant digits). WCSHDO_P13: Use "%21.13G" format for all floating- point keyvalues (13 significant digits). WCSHDO_P14: Use "%22.14G" format for all floating- point keyvalues (14 significant digits). WCSHDO_P15: Use "%23.15G" format for all floating- point keyvalues (15 significant digits). WCSHDO_P16: Use "%24.16G" format for all floating- point keyvalues (16 significant digits). WCSHDO_P17: Use "%25.17G" format for all floating- point keyvalues (17 significant digits). If more than one of the above flags are set, the highest number of significant digits prevails. In addition, there is an anciliary flag: WCSHDO_EFMT: Use "E" format instead of the default "G" format above. Note that excess trailing zeroes are stripped off the fractional part with "G" (which never occurs with "E"). Note also that the higher-precision options eat into the keycomment area. In this regard, WCSHDO_P14 causes minimal disruption with "G" format, while WCSHDO_P13 is appropriate with "E".
  [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 freed by the user to avoid memory leaks. See wcsdealloc(). 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:

1. 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

## ◆ wcshdr_errmsg

const char* wcshdr_errmsg[]
| extern

Status return messages.

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