Preparing FITS Images for use by IRAS90 and KAPPA

The starting point for this process depends on where the data is stored. If the data is in a FITS file on magnetic tape, then KAPPA:FITSIN (i.e. the FITSIN application from the KAPPA package) should be used to create an NDF holding the data. If the data is in a FITS file on disk, then KAPPA:FITSDIN should be used. Both of these applications create an NDF holding the main data array and key words from the FITS file. However, the FITS keywords are not at this point stored in a form in which they can easily be accessed by IRAS90 applications. In addition, some IRAS FITS files contain images in an inconvenient form (CPC images for instance are stored in a three dimensional stack, and SKYFLUX images are stored ``flipped'' so that north is downwards). To circumvent these problems, the output from KAPPA:FITSIN (or FITSDIN) should be processed using IRAS90 application PREPARE. One of the major tasks accomplished by PREPARE is to create an ``astrometry structure'' within the NDF which describes the position on the sky of each pixel in the image. This structure is needed if any of the astrometric applications within IRAS90 (such as SKYGRID, SKYPOS, etc) are to be used.