Automatic Format Conversion with the NDF Library

SSN/20 describes a system incorporated into the NDF library routines which enables applications written to read or write NDFs to handle any arbitrary ‘foreign’ format for which a conversion utility can be defined. The system operates via environment variables which define the set of permitted conversions and the commands required to do them.

3.1 The Default Conversion Commands

Convert startup will define defaults for the NDF-conversion environment variables which permit automatic conversion of files in the formats handled by Convert (except for AST, IRCAM, PGM. SPECX and FITS tapes). It also allows data compression.

The list of format names and associated filename extensions defined by Convert is set out in Table 1—the filename extensions tell the system which format the file is in. For the unformatted and ASCII conversions the format names and extensions are somewhat arbitrary. This list will nullify any existing list so private conversions must be added after Convert startup.

For the unformatted and ASCII conversions the format names and extensions are somewhat arbitrary. The FITS and STREAM formats have synonym file extensions for the conversion to NDF. The standard file extension is required for the conversion to the foreign format.


Format	Extension	Extension	Description
		Synonyms

FITS	.fit	.fits .fts .FITS .FIT .lilo .lihi .silo .sihi .mxlo .mxhi .rilo .rihi .vdlo .vdhi	FITS
FIGARO	.dst		Figaro (Version 2) DST
IRAF	.imh		IRAF
STREAM	.das	.str	Unformatted direct-access or stream
UNFORMATTED	.unf		Unformatted with FITS header
UNF0	.dat		Unformatted without FITS header
ASCII	.asc		ASCII with FITS header
TEXT	.txt		ASCII without FITS header
GIF	.gif		Graphics Interchange Format
TIFF	.tif		Tag Image File Format
GASP	.hdr		GASP
COMPRESSED	.sdf.Z		Compressed NDF
GZIP	.sdf.gz		gzip compressed NDF

Table 1: Defined Formats and Extensions

Table 2 lists the utilities used to perform the conversions. In general the default parameter values are used—non-default parameters (other than the input and output filenames) are listed in the table.


FORMAT	In/out	Utility	Non-default parameters	Variable

FITS	in	FITS2NDF
	out	NDF2FITS	bitpix=-1 proexts=t
FIGARO	in	DST2NDF
	out	NDF2DST		$\times$
IRAF	in	??
	out	NDF2IRAF
STREAM	in	DA2NDF	noperec=!
	out	NDF2DA
UNFORMATTED	in	UNF2NDF	fits=t noperec=!
	out	NDF2UNF	fits=t
UNF0	in	UNF2NDF	fits=f noperec=!	$\sqrt$
	out	NDF2UNF	fits=f
ASCII	in	ASCII2NDF	fits=t
	out	NDF2ASCII	fits=t reclen=80
TEXT	in	ASCII2NDF	fits=f	$\sqrt$
	out	NDF2ASCII	fits=f reclen=80
GIF	in	GIF2NDF		$\times$
	out	NDF2GIF		$\times$
TIFF	in	TIFF2NDF		$\times$
	out	NDF2TIFF		$\times$
GASP	in	GASP2NDF
	out	NDF2GASP	fillbad=0
COMPRESSED	in	uncompress		$\times$
	out	compress		$\times$
GZIP	in	gzip		$\times$
	out	gunzip		$\times$

Table 2: Conversion Commands.

Table 2 also contains a column headed ‘Variable’. Most of the command lines issued to do the automatic conversion will include the translation of an environment variable named NDF_FROM_fmt_PARS or NDF_TO_fmt_PARS as appropriate (where fmt is the format name). This may be used to give additional parameters to the command if you do not want to define a completely new command for yourself.

Where the ‘Variable’ column contains a tick, the variable must be used to supply the SHAPE parameter; where it contains a cross, additional parameters cannot be specified.

For example, suppose application rdndf uses the NDF library to read one NDF (named by the first parameter) and write another (named by the second parameter). This application could be made to read a TEXT file (data.txt) containing the required values for a 50

$\times$ 10 data array, and write its results as a FITS file (output.fit) as follows:

  % convert
  CONVERT commands are now available -- (Version 1.4, 2001 November)

  Defaults for automatic NDF conversion are set.

  Type conhelp for help on CONVERT commands.
  Type "showme sun55" to browse the hypertext documentation.

  % setenv NDF_FROM_TEXT_PARS ’SHAPE=[50,10]’
  % rdndf data.txt output.fit

The order of the formats in the tables also defines a search path. If you omit the file extension, the system will search for an NDF of that name. If that is absent, it will try a .fit FITS file. If neither are present it tries an IRAF file, and so on. The recognised formats and their order is defined through the environment variable NDF_FORMATS_IN. The shell convert startup defines NDF_FORMATS_IN as given below.

       ’FITS(.fit),FIGARO(.dst),IRAF(.imh),STREAM(.das),UNFORMATTED(.unf),
       UNF0(.dat),ASCII(.asc),TEXT(.txt),GIF(.gif),TIFF(.tif),GASP(.hdr),
       COMPRESSED(.sdf.Z),GZIP(.sdf.gz),FITS(.fits),FITS(.fts),FITS(.FTS),
       FITS(.FITS),FITS(.FIT),FITS(.lilo),FITS(.lihi),
       FITS(.silo),FITS(.sihi),FITS(.mxlo),FITS(.mxhi),
       FITS(.rilo),FITS(.rihi),FITS(.vdlo),FITS(.vdhi),STREAM(.str)’

but from ICL the CONVERT command does not define the synonyms due to a limitation of ICL. Thus NDF_FORMATS_IN is defined to be the following.

When creating an output file, there is a similar list of recognised formats. The Convert startup procedures define NDF_FORMATS_OUT as follows.

The leading dot indicates that if you omit the file extension, the output file will be an NDF.

There are some examples of the automatic system in action and use of NDF_FORMATS_IN and NDF_FORMATS_OUT in SUN/95, Section 15.1.

3 Automatic Format Conversion with the NDF Library

3.1 The Default Conversion Commands