6.5 Data Scaling and Undefined Pixel Parameters
These subroutines define or modify the internal parameters used by
FITSIO to either scale the data or to represent undefined pixels.
Generally FITSIO will scale the data according to the values of the BSCALE
and BZERO (or TSCALn and TZEROn) keywords, however these subroutines
may be used to override the keyword values. This may be useful when
one wants to read or write the raw unscaled values in the FITS file.
Similarly, FITSIO generally uses the value of the BLANK or TNULLn
keyword to signify an undefined pixel, but these routines may be used
to override this value. These subroutines do not create or modify the
corresponding header keyword values.
- 1
- Reset the scaling factors in the primary array or image extension; does
not change the BSCALE and BZERO keyword values and only affects the
automatic scaling performed when the data elements are written/read
to/from the FITS file. When reading from a FITS file the returned
data value = (the value given in the FITS array) * BSCALE + BZERO.
The inverse formula is used when writing data values to the FITS
file. (NOTE: BSCALE and BZERO must be declared as Double Precision
variables).
FTPSCL(unit,bscale,bzero, > status)
- 2
- Reset the scaling parameters for a table column; does not change
the TSCALn or TZEROn keyword values and only affects the automatic
scaling performed when the data elements are written/read to/from
the FITS file. When reading from a FITS file the returned data
value = (the value given in the FITS array) * TSCAL + TZERO. The
inverse formula is used when writing data values to the FITS file.
(NOTE: TSCAL and TZERO must be declared as Double Precision
variables).
FTTSCL(unit,colnum,tscal,tzero, > status)
- 3
- Define the integer value to be used to signify undefined pixels in the
primary array or image extension. This is only used if BITPIX = 8, 16,
32. or 64 This does not create or change the value of the BLANK keyword in
the header. FTPNULLL is identical to FTPNUL except that the blank
value is a 64-bit integer instead of a 32-bit integer.
FTPNUL(unit,blank, > status)
FTPNULLL(unit,blankll, > status)
- 4
- Define the string to be used to signify undefined pixels in
a column in an ASCII table. This does not create or change the value
of the TNULLn keyword.
FTSNUL(unit,colnum,snull > status)
- 5
- Define the value to be used to signify undefined pixels in
an integer column in a binary table (where TFORMn = 'B', 'I', 'J', or 'K').
This does not create or change the value of the TNULLn keyword.
FTTNULLL is identical to FTTNUL except that the tnull
value is a 64-bit integer instead of a 32-bit integer.
FTTNUL(unit,colnum,tnull > status)
FTTNULLL(unit,colnum,tnullll > status)