FITSET-Set the value of a FITS keyword

Description:

FIGARO program to set (or modify) a FITS keyword in a Figaro file. This program accepts the name of a single FITS keyword and a new value for it. If the keyword already exists it will be changed, unless it is one of the special keywords ("HISTORY", "COMMENT", or 'blank') that can have multiple values, in which case the new value will be added to those already in the file.

Parameters:

FILE

The name of the Figaro file one of whose keywords is to be changed.

KEYWORD

The name of the FITS keyword to be set or modified. If the keyword already exists it will be listed by the program. Note that FITS keyword names should be limited to 8 characters in length, but this is not enforced by this program. Note: if you set the value of one of the standard keywords that can be deduced from the rest of the data in the file, such as 'NAXIS' or 'CRDELTn' or 'BITPIX' you may get confusing results. This is not recommended.

VALUE

The new value for the FITS keyword specified. This is specified as a character string, so may need to be given enclosed by quotes. Note that the FITS standard limits character values to upper case, so any lower case characters will be folded to upper case. If the value is to be treated as a logical value, it should be either 'T' or 'F'. Numeric and logical values are treated slightly differently to the way string values are treated. By default, if the value given can be interpreted as a number by FITSET then it will be; otherwise it will be treated as a literal string. This can be overriden by the STRING and LOGICAL keywords.

COMMENT

Each FITS keyword has a comment string associated with it. COMMENT supplies the comment string to be associated with the KEYWORD being set. If a keyword already exists, then the exisitng comment (if any) is used as the default comment.

LOGICAL

If LOGICAL is set, then FITSET will treat the supplied value as a logical one. In this case the string supplied for VALUE must have been either 'T' or 'F'. Logical values are stored internally in FITS files slightly differently to the way string values are treated. In most cases, this doesn't matter much, but systems other than Figaro may be fussy about the types of specific keywords.

STRING

If STRING is set, then FITSET will treat the supplied value as a literal character string, even if it can be interpreted as a number. Numeric values are stored internally in FITS files slightly differently to the way string values are treated. In most cases, this doesn't matter much, but systems other than Figaro may be fussy about the types of specific keywords.

Source comments:

 F I T S E T

 Function:
    Figaro routine to set (or modify) a FITS keyword in a file.

 Description:
    This routine allows a FITS keyword in a file to be set or, if it
    already exists, to be modified. This routine is needed mainly because
    of the difficulty of changing items in a FITS header when the file
    in question is in NDF format. (A .DST file has the FITS information
    in separate structure items which can easily be modified using LET,
    but an NDF format file has all the FITS keywords in a single
    character array which is not amenable to such changes.)

 Invocation:
    FITSET file keyword value comment [logical] [string]

 Parameters:
    file     (Filename) The name of the Figaro format file in which the
             keyword is to be set.
    keyword  (Character string) The name of the FITS keyword that is to be
             set.
    value    (Character string) The new value of the FITS keyword. If
             this can be interpreted as a numeric value it will be set as
             such. Otherwise it will be kept as a character string.
    comment  (Character string) The comment to be associated with the
             keyword.
    logical  (Keyword) If set, forces the value to be treated as a logical
             value, in which case it must be one of 'T' or 'F' and will
             be set as such in the output file.
    string   (Keyword) If set, forces the value to be treated as a literal
             string; in this case it will not be treated as a number even if
             it can be.

    Keith Shortridge, AAO.