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wcsunits.h
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/*============================================================================
WCSLIB 8.5 - an implementation of the FITS WCS standard.
Copyright (C) 1995-2025, Mark Calabretta
This file is part of WCSLIB.
WCSLIB is free software: you can redistribute it and/or modify it under the
terms of the GNU Lesser General Public License as published by the Free
Software Foundation, either version 3 of the License, or (at your option)
any later version.
WCSLIB is distributed in the hope that it will be useful, but WITHOUT ANY
WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for
more details.
You should have received a copy of the GNU Lesser General Public License
along with WCSLIB. If not, see http://www.gnu.org/licenses.
Author: Mark Calabretta, Australia Telescope National Facility, CSIRO.
http://www.atnf.csiro.au/people/Mark.Calabretta
$Id: wcsunits.h,v 8.5 2025/12/06 13:47:41 mcalabre Exp $
*=============================================================================
*
* WCSLIB 8.5 - C routines that implement the FITS World Coordinate System
* (WCS) standard. Refer to the README file provided with WCSLIB for an
* overview of the library.
*
*
* Summary of the wcsunits routines
* --------------------------------
* Routines in this suite deal with units specifications and conversions, as
* described in
*
= "Representations of world coordinates in FITS",
= Greisen, E.W., & Calabretta, M.R. 2002, A&A, 395, 1061 (WCS Paper I)
*
* The Flexible Image Transport System (FITS), a data format widely used in
* astronomy for data interchange and archive, is described in
*
= "Definition of the Flexible Image Transport System (FITS), version 3.0",
= Pence, W.D., Chiappetti, L., Page, C.G., Shaw, R.A., & Stobie, E. 2010,
= A&A, 524, A42 - http://dx.doi.org/10.1051/0004-6361/201015362
*
* See also http://fits.gsfc.nasa.gov
*
* These routines perform basic units-related operations:
*
* - wcsunitse(): given two unit specifications, derive the conversion from
* one to the other.
*
* - wcsutrne(): translates certain commonly used but non-standard unit
* strings. It is intended to be called before wcsulexe() which only
* handles standard FITS units specifications.
*
* - wcsulexe(): parses a standard FITS units specification of arbitrary
* complexity, deriving the conversion to canonical units.
*
*
* wcsunitse() - FITS units specification conversion
* -------------------------------------------------
* wcsunitse() derives the conversion from one system of units to another.
*
* A deprecated form of this function, wcsunits(), lacks the wcserr**
* parameter.
*
* Given:
* have const char []
* FITS units specification to convert from (null-
* terminated), with or without surrounding square
* brackets (for inline specifications); text following
* the closing bracket is ignored.
*
* want const char []
* FITS units specification to convert to (null-
* terminated), with or without surrounding square
* brackets (for inline specifications); text following
* the closing bracket is ignored.
*
* Returned:
* scale,
* offset,
* power double* Convert units using
*
= pow(scale*value + offset, power);
*
* Normally offset is zero except for log() or ln()
* conversions, e.g. "log(MHz)" to "ln(Hz)". Likewise,
* power is normally unity except for exp() conversions,
* e.g. "exp(ms)" to "exp(/Hz)". Thus conversions
* ordinarily consist of
*
= value *= scale;
*
* err struct wcserr **
* If enabled, for function return values > 1, this
* struct will contain a detailed error message, see
* wcserr_enable(). May be NULL if an error message is
* not desired. Otherwise, the user is responsible for
* deleting the memory allocated for the wcserr struct.
*
* Function return value:
* int Status return value:
* 0: Success.
* 1-9: Status return from wcsulexe().
* 10: Non-conformant unit specifications.
* 11: Non-conformant functions.
*
* scale is zeroed on return if an error occurs.
*
*
* wcsutrne() - Translation of non-standard unit specifications
* ------------------------------------------------------------
* wcsutrne() translates certain commonly used but non-standard unit strings,
* e.g. "DEG", "MHZ", "KELVIN", that are not recognized by wcsulexe(), refer to
* the notes below for a full list. Compounds are also recognized, e.g.
* "JY/BEAM" and "KM/SEC/SEC". Extraneous embedded blanks are removed.
*
* A deprecated form of this function, wcsutrn(), lacks the wcserr** parameter.
*
* Given:
* ctrl int Although "S" is commonly used to represent seconds,
* its translation to "s" is potentially unsafe since the
* standard recognizes "S" formally as Siemens, however
* rarely that may be used. The same applies to "H" for
* hours (Henry), and "D" for days (Debye). This
* bit-flag controls what to do in such cases:
* 1: Translate "S" to "s".
* 2: Translate "H" to "h".
* 4: Translate "D" to "d".
* Thus ctrl == 0 doesn't do any unsafe translations,
* whereas ctrl == 7 does all of them.
*
* Given and returned:
* unitstr char [] Null-terminated character array containing the units
* specification to be translated.
*
* Inline units specifications in a FITS header
* keycomment are also handled. If the first non-blank
* character in unitstr is '[' then the unit string is
* delimited by its matching ']'. Blanks preceding '['
* will be stripped off, but text following the closing
* bracket will be preserved without modification.
*
* err struct wcserr **
* If enabled, for function return values > 1, this
* struct will contain a detailed error message, see
* wcserr_enable(). May be NULL if an error message is
* not desired. Otherwise, the user is responsible for
* deleting the memory allocated for the wcserr struct.
*
* Function return value:
* int Status return value:
* -1: No change was made, other than stripping blanks
* (not an error).
* 0: Success.
* 9: Internal parser error.
* 12: Potentially unsafe translation, whether applied
* or not (see notes).
*
* Notes:
* 1: Translation of non-standard unit specifications: apart from leading and
* trailing blanks, a case-sensitive match is required for the aliases
* listed below, in particular the only recognized aliases with metric
* prefixes are "KM", "KHZ", "MHZ", and "GHZ". Potentially unsafe
* translations of "D", "H", and "S", shown in parentheses, are optional.
*
= Unit Recognized aliases
= ---- ----------------------------------------------------------
= Angstrom Angstroms angstrom angstroms
= arcmin arcmins, ARCMIN, ARCMINS
= arcsec arcsecs, ARCSEC, ARCSECS
= beam BEAM
= byte Byte
= d day, days, (D), DAY, DAYS
= deg degree, degrees, Deg, Degree, Degrees, DEG, DEGREE,
= DEGREES
= GHz GHZ
= h hr, (H), HR
= Hz hz, HZ
= kHz KHZ
= Jy JY
= K kelvin, kelvins, Kelvin, Kelvins, KELVIN, KELVINS
= km KM
= m metre, meter, metres, meters, M, METRE, METER, METRES,
= METERS
= min MIN
= MHz MHZ
= Ohm ohm
= Pa pascal, pascals, Pascal, Pascals, PASCAL, PASCALS
= pixel pixels, PIXEL, PIXELS
= rad radian, radians, RAD, RADIAN, RADIANS
= s sec, second, seconds, (S), SEC, SECOND, SECONDS
= V volt, volts, Volt, Volts, VOLT, VOLTS
= yr year, years, YR, YEAR, YEARS
*
* The aliases "angstrom", "ohm", and "Byte" for (Angstrom, Ohm, and byte)
* are recognized by wcsulexe() itself as an unofficial extension of the
* standard, but they are converted to the standard form here.
*
*
* wcsulexe() - FITS units specification parser
* --------------------------------------------
* wcsulexe() parses a standard FITS units specification of arbitrary
* complexity, deriving the scale factor required to convert to canonical
* units - basically SI with degrees and "dimensionless" additions such as
* byte, pixel and count.
*
* A deprecated form of this function, wcsulex(), lacks the wcserr** parameter.
*
* Given:
* unitstr const char []
* Null-terminated character array containing the units
* specification, with or without surrounding square
* brackets (for inline specifications); text following
* the closing bracket is ignored.
*
* Returned:
* func int* Special function type, see note 4:
* 0: None
* 1: log() ...base 10
* 2: ln() ...base e
* 3: exp()
*
* scale double* Scale factor for the unit specification; multiply a
* value expressed in the given units by this factor to
* convert it to canonical units.
*
* units double[WCSUNITS_NTYPE]
* A units specification is decomposed into powers of 16
* fundamental unit types: angle, mass, length, time,
* count, pixel, etc. Preprocessor macro WCSUNITS_NTYPE
* is defined to dimension this vector, and others such
* WCSUNITS_PLANE_ANGLE, WCSUNITS_LENGTH, etc. to access
* its elements.
*
* Corresponding character strings, wcsunits_types[] and
* wcsunits_units[], are predefined to describe each
* quantity and its canonical units.
*
* err struct wcserr **
* If enabled, for function return values > 1, this
* struct will contain a detailed error message, see
* wcserr_enable(). May be NULL if an error message is
* not desired. Otherwise, the user is responsible for
* deleting the memory allocated for the wcserr struct.
*
* Function return value:
* int Status return value:
* 0: Success.
* 1: Invalid numeric multiplier.
* 2: Dangling binary operator.
* 3: Invalid symbol in INITIAL context.
* 4: Function in invalid context.
* 5: Invalid symbol in EXPON context.
* 6: Unbalanced bracket.
* 7: Unbalanced parenthesis.
* 8: Consecutive binary operators.
* 9: Internal parser error.
*
* scale and units[] are zeroed on return if an error
* occurs.
*
* Notes:
* 1: wcsulexe() is permissive in accepting whitespace in all contexts in a
* units specification where it does not create ambiguity (e.g. not
* between a metric prefix and a basic unit string), including in strings
* like "log (m ** 2)" which is formally disallowed.
*
* 2: Supported extensions:
* - "angstrom" (OGIP usage) is allowed in addition to "Angstrom".
* - "ohm" (OGIP usage) is allowed in addition to "Ohm".
* - "Byte" (common usage) is allowed in addition to "byte".
*
* 3: Table 6 of WCS Paper I lists eleven units for which metric prefixes are
* allowed. However, in this implementation only prefixes greater than
* unity are allowed for "a" (annum), "yr" (year), "pc" (parsec), "bit",
* and "byte", and only prefixes less than unity are allowed for "mag"
* (stellar magnitude).
*
* Metric prefix "P" (peta) is specifically forbidden for "a" (annum) to
* avoid confusion with "Pa" (Pascal, not peta-annum). Note that metric
* prefixes are specifically disallowed for "h" (hour) and "d" (day) so
* that "ph" (photons) cannot be interpreted as pico-hours, nor "cd"
* (candela) as centi-days.
*
* 4: Function types log(), ln() and exp() may only occur at the start of the
* units specification. The scale and units[] returned for these refers
* to the string inside the function "argument", e.g. to "MHz" in log(MHz)
* for which a scale of 1e6 will be returned.
*
*
* Global variable: const char *wcsunits_errmsg[] - Status return messages
* -----------------------------------------------------------------------
* Error messages to match the status value returned from each function.
*
*
* Global variable: const char *wcsunits_types[] - Names of physical quantities
* ----------------------------------------------------------------------------
* Names for physical quantities to match the units vector returned by
* wcsulexe():
* - 0: plane angle
* - 1: solid angle
* - 2: charge
* - 3: mole
* - 4: temperature
* - 5: luminous intensity
* - 6: mass
* - 7: length
* - 8: time
* - 9: beam
* - 10: bin
* - 11: bit
* - 12: count
* - 13: stellar magnitude
* - 14: pixel
* - 15: solar ratio
* - 16: voxel
*
*
* Global variable: const char *wcsunits_units[] - Names of units
* --------------------------------------------------------------
* Names for the units (SI) to match the units vector returned by wcsulexe():
* - 0: degree
* - 1: steradian
* - 2: Coulomb
* - 3: mole
* - 4: Kelvin
* - 5: candela
* - 6: kilogram
* - 7: metre
* - 8: second
*
* The remainder are dimensionless.
*===========================================================================*/
#ifndef WCSLIB_WCSUNITS
#define WCSLIB_WCSUNITS
#include "wcserr.h"
#ifdef __cplusplus
extern "C" {
#endif
extern const char *wcsunits_errmsg[];
enum wcsunits_errmsg_enum {
UNITSERR_SUCCESS = 0, // Success.
UNITSERR_BAD_NUM_MULTIPLIER = 1, // Invalid numeric multiplier.
UNITSERR_DANGLING_BINOP = 2, // Dangling binary operator.
UNITSERR_BAD_INITIAL_SYMBOL = 3, // Invalid symbol in INITIAL context.
UNITSERR_FUNCTION_CONTEXT = 4, // Function in invalid context.
UNITSERR_BAD_EXPON_SYMBOL = 5, // Invalid symbol in EXPON context.
UNITSERR_UNBAL_BRACKET = 6, // Unbalanced bracket.
UNITSERR_UNBAL_PAREN = 7, // Unbalanced parenthesis.
UNITSERR_CONSEC_BINOPS = 8, // Consecutive binary operators.
UNITSERR_PARSER_ERROR = 9, // Internal parser error.
UNITSERR_BAD_UNIT_SPEC = 10, // Non-conformant unit specifications.
UNITSERR_BAD_FUNCS = 11, // Non-conformant functions.
UNITSERR_UNSAFE_TRANS = 12 // Potentially unsafe translation.
};
extern const char *wcsunits_types[];
extern const char *wcsunits_units[];
#define WCSUNITS_PLANE_ANGLE 0
#define WCSUNITS_SOLID_ANGLE 1
#define WCSUNITS_CHARGE 2
#define WCSUNITS_MOLE 3
#define WCSUNITS_TEMPERATURE 4
#define WCSUNITS_LUMINTEN 5
#define WCSUNITS_MASS 6
#define WCSUNITS_LENGTH 7
#define WCSUNITS_TIME 8
#define WCSUNITS_BEAM 9
#define WCSUNITS_BIN 10
#define WCSUNITS_BIT 11
#define WCSUNITS_COUNT 12
#define WCSUNITS_MAGNITUDE 13
#define WCSUNITS_PIXEL 14
#define WCSUNITS_SOLRATIO 15
#define WCSUNITS_VOXEL 16
#define WCSUNITS_NTYPE 17
int wcsunitse(const char have[], const char want[], double *scale,
double *offset, double *power, struct wcserr **err);
int wcsutrne(int ctrl, char unitstr[], struct wcserr **err);
int wcsulexe(const char unitstr[], int *func, double *scale,
double units[WCSUNITS_NTYPE], struct wcserr **err);
// Deprecated.
int wcsunits(const char have[], const char want[], double *scale,
double *offset, double *power);
int wcsutrn(int ctrl, char unitstr[]);
int wcsulex(const char unitstr[], int *func, double *scale,
double units[WCSUNITS_NTYPE]);
#ifdef __cplusplus
}
#endif
#endif // WCSLIB_WCSUNITS
wcserr
Error message handling.
Definition wcserr.h:243
wcserr.h
wcsunits_errmsg
const char * wcsunits_errmsg[]
Status return messages.
wcsutrne
int wcsutrne(int ctrl, char unitstr[], struct wcserr **err)
Translation of non-standard unit specifications.
wcsunitse
int wcsunitse(const char have[], const char want[], double *scale, double *offset, double *power, struct wcserr **err)
FITS units specification conversion.
wcsutrn
int wcsutrn(int ctrl, char unitstr[])
wcsunits_units
const char * wcsunits_units[]
Names of units.
wcsulexe
int wcsulexe(const char unitstr[], int *func, double *scale, double units[WCSUNITS_NTYPE], struct wcserr **err)
FITS units specification parser.
WCSUNITS_NTYPE
#define WCSUNITS_NTYPE
Number of entries in the units array.
Definition wcsunits.h:386
wcsunits_errmsg_enum
wcsunits_errmsg_enum
Definition wcsunits.h:349
UNITSERR_BAD_EXPON_SYMBOL
@ UNITSERR_BAD_EXPON_SYMBOL
Definition wcsunits.h:355
UNITSERR_PARSER_ERROR
@ UNITSERR_PARSER_ERROR
Definition wcsunits.h:359
UNITSERR_UNBAL_BRACKET
@ UNITSERR_UNBAL_BRACKET
Definition wcsunits.h:356
UNITSERR_UNBAL_PAREN
@ UNITSERR_UNBAL_PAREN
Definition wcsunits.h:357
UNITSERR_BAD_NUM_MULTIPLIER
@ UNITSERR_BAD_NUM_MULTIPLIER
Definition wcsunits.h:351
UNITSERR_BAD_FUNCS
@ UNITSERR_BAD_FUNCS
Definition wcsunits.h:361
UNITSERR_CONSEC_BINOPS
@ UNITSERR_CONSEC_BINOPS
Definition wcsunits.h:358
UNITSERR_DANGLING_BINOP
@ UNITSERR_DANGLING_BINOP
Definition wcsunits.h:352
UNITSERR_FUNCTION_CONTEXT
@ UNITSERR_FUNCTION_CONTEXT
Definition wcsunits.h:354
UNITSERR_SUCCESS
@ UNITSERR_SUCCESS
Definition wcsunits.h:350
UNITSERR_BAD_UNIT_SPEC
@ UNITSERR_BAD_UNIT_SPEC
Definition wcsunits.h:360
UNITSERR_UNSAFE_TRANS
@ UNITSERR_UNSAFE_TRANS
Definition wcsunits.h:362
UNITSERR_BAD_INITIAL_SYMBOL
@ UNITSERR_BAD_INITIAL_SYMBOL
Definition wcsunits.h:353
wcsulex
int wcsulex(const char unitstr[], int *func, double *scale, double units[WCSUNITS_NTYPE])
wcsunits_types
const char * wcsunits_types[]
Names of physical quantities.
wcsunits
int wcsunits(const char have[], const char want[], double *scale, double *offset, double *power)