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Subroutines to specify the structure of a new HDU

1

Reserve space in the CHU for MOREKEYS more header keywords. This subroutine may be called to reserve space for keywords which are to be written at a later time, after the data unit or subsequent extensions have been written to the FITS file. If this subroutine is not explicitly called, then the initial size of the FITS header will be limited to the space available at the time that the first data is written to the associated data unit. FITSIO has the ability to dynamically add more space to the header if needed, however it is more efficient to preallocate the required space if the size is known in advance.

FTHDEF(unit,morekeys, > status)

2

Define the structure of the primary array or IMAGE extension

FTPDEF(unit,bitpix,naxis,naxes,pcount,gcount, > status)

3

Define the structure of an ASCII table (TABLE) extension

FTADEF(unit,rowlen,tfields,tbcol,tform,nrows > status)

4

Define the structure of a binary table (BINTABLE) extension

FTBDEF(unit,tfields,tform,varidat,nrows > status)

5

Define the zero indexed byte offset of the 'heap' measured from the start of the binary table data. By default the heap is assumed to start immediately following the regular table data, i.e., at location NAXIS1 x NAXIS2. This routine is only relevant for binary tables which contain variable length array columns (with TFORMnnn = 'Pt'). This subroutine also automatically writes the value of theap to a keyword in the extension header. This subroutine must be called after the required keywords have been written (with ftphbn) and after the table structure has been defined (with ftbdef) but before any data is written to the table.

FTPTHP(unit,theap, > status)

6

Define the size of the Current Data Unit, overriding the length of the data unit as previously defined by ftpdef, ftadef, or ftbdef. This is useful if one does not know the total size of the data unit until after the data have been written. The size (in bytes) of an ASCII or Binary table is given by NAXIS1 * NAXIS2. (Note that to determine the value of NAXIS1 it is often more convenient to read the value of the NAXIS1 keyword from the output file, rather than computing the row length directly from all the TFORM keyword values).

FTDDEF(unit,bytlen, > status)

7

Redefine the size of the Current Data Unit and override the length of the data unit as previously defined by ftpdef, ftadef, or ftbdef. This routine forces FITSIO to reread the values of the NAXISn (and PCOUNT and GCOUNT) keywords and recompute the total size of the data unit. This subroutine serves the same purpose as the FTDDEF subroutine, but is easier to use since it is not necessary for the user to compute the size of the data unit.

FTRDEF(unit, > status)