idlastro / FITS ASCII & Binary Table I/O: FTHMOD

[Source code]

NAME
FTHMOD
PURPOSE
Procedure to modify header information for a specified field
in a FITS table.
CALLING SEQUENCE
fthmod, h, field, parameter, value
INPUT
h - FITS header for the table
field - field name or number
parameter - string name of the parameter to modify.  Choices
        include:
                TTYPE - field name
                TUNIT - physical units for field (eg. 'ANGSTROMS')
                TNULL - null value (string) for field, (eg. '***')
                TFORM - format specification for the field
                TSCAL - scale factor
                TZERO - zero offset
        User should be aware that the validity of the change is
        not checked.  Unless you really know what you are doing,
        this routine should only be used to change field names,
        units, or another user specified parameter.
value - new value for the parameter.  Refer to the FITS table
        standards documentation for valid values.
EXAMPLE
Change the units for a field name "FLUX" to "Janskys" in a FITS table
  header,h
IDL> FTHMOD, h, 'FLUX', 'TUNIT','Janskys' 
METHOD
The header keyword  is modified
with the new value.
HISTORY
version 1, D. Lindler  July 1987
Converted to IDL V5.0   W. Landsman   September 1997
Major rewrite to use new FTINFO call   W. Landsman   May 2000