Name Your Formats

The first step in setting up the NDF library to access foreign data formats is to define a name for each foreign format to be recognised, and to associate a file extension with each of these names. The file extension will be used to determine which format a file is written in.

This is done by defining the environment variable called NDF_FORMATS_IN to contain a format list, such as the following:

setenv NDF_FORMATS_IN 'FITS(.fit),FIGARO(.dst),IRAF(.imh)'

This is a comma-separated list of format specifications, where each specification consists of a format name (e.g. FITS) with an associated file extension (e.g. `.fit') in parentheses.

This list serves two purposes. First, it defines the set of formats and associated file extensions to be recognised when accessing input² datasets. This means, for instance, that if a dataset name such as:

run66.fit

were given to the NDF library, it would recognise it as a FITS format file and try to carry out the appropriate conversion.

The list also defines a search order for foreign data formats. This means that if the dataset name supplied had been simply:

run66

then the NDF library would first look for a native format NDF with this name (i.e. in the file run66.sdf). If this was not found, it would then look for a file called run66.fit, then run66.dst and then run66.imh, stopping when the first one was found and associating the appropriate data format with it. If none of the files existed, a ``file not found'' error would result.

Note that the ability to select sections from pre-existing NDF datasets (see SUN/33) is also available when accessing foreign data files, so that entering:

run66.fit(100.0$\sim$50.0)

or

run66(100.0:200.0,10:512)

would result in the same actions as above to locate a suitable file and to convert its format, with the required section then being extracted from the converted NDF and passed to the application.