Exporting maps

After the data have been regridded with rebin the image can then be analysed with an image-analysis tool. Obviously KAPPA, FIGARO [25] or GAIA can be used immediately since they support the NDF standard.

In order to use packages such as IRAF, AIPS or MIRIAD the data must first be converted to FITS format by using either the CONVERT task ndf2fits or the FIGARO task wdfits. The ndf2fits task is recommended since it can understand FITS tables, floating-point FITS, and the new AST extension [20]¹¹

For images rebinned with an older version of SURF (pre-1.3) or if using wdfits or a version of CONVERT that does not understand AST (pre-1.1) it is necessary to remove the AXIS components from the NDF before converting since the axis information (arcsec offsets from the map centre) takes priority. In order to propagate WCS astrometry information from the NDF FITS array into the FITS file the axis information must first be removed by using FIGARO's delobj or KAPPA's setaxis. For example, if the image is stored in file scuba_image.sdf and we wish to convert this to an integer FITS file scuba_image.fits, with KAPPA/CONVERT we would do:

% kappa
% convert
% setaxis scuba_image mode=delete
% ndf2fits bitpix=32 profits scuba_image scuba_image.fits

The PROFITS parameter is there to ensure that all the FITS information in the NDF is propagated to the FITS file. With FIGARO we would do:

% figaro
% delobj scuba_image.axis
% wdfits scuba_image scuba_image.fits

Note that wdfits always writes integer FITS whereas ndf2fits would by default write REAL FITS (bitpix=$-32$). ndf2fits also writes the Variance and Quality arrays to FITS tables in the output file (this can be turned off by specifying just the data component with COMP=D).

From KAPPA V0.13 the WCS information stored in the header is used when manipulating the NDF. As of SURF version 1.4, the astrometry information is no longer stored in IRAS90 or FITS extensions; all astrometry information can be found in the AST/WCS component which is understood by KAPPA, GAIA and ndf2fits.