Keywords: gildas-intro

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## From and To other Packages: FITS

For astronomical applications, conversion from other data formats can be done through FITS format. The FITS image must reside on disk.

Disk FITS conversion can be a non-trivial task is the input FITS file has a complex structure. Several tools are thus available

- `FITS_GILDAS` (FITS to GILDAS) and `GILDAS_FITS` (GILDAS to FITS) Tasks can process simple FITS files

- `VECTORFITS FitsFile.fits FROM|TO GildasImage.gdf`
  provide a command line equivalent to the above tasks. Since FITS keywords are not fully normalized, although a standard subset is recommended, this command supports keyword redefinition. If you receive a tape with source name coded as `SOURCE` (instead of `OBJECT`), all you need to do is to define a SIC symbol named `SOURCE` with translation `OBJECT`. This is done simply by typing the command

          SIC\SYMBOL SOURCE OBJECT

  This trick does not work with the `FITS_GILDAS` task.

- `SICDEFINE FITS Var FitsFile` is similar to DEFINE IMAGE, and will create a SIC structure which will copy the FITS file content. The LET command can be then used to copy (part of) this structure into an Image variable if needed, and thus convert to the image format. It only works on existing FITS file however, and cannot be used to create a FITS file from a SIC structure.

- `SICDEFINE IMAGE` will automatically attempt to convert a FITS file into the Gildas equivalent, using the same method as FITS_GILDAS. This will work transparently on simple FITS images (with no FITS XTENSION).

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