Setting reduction information

Before you can ask CCDPACK to schedule a reduction it is necessary to put your data frames through a process known as ``importing''. What this means is that all the necessary descriptions about the type of data (target, bias, flat etc.), filter, where the CCD bias strips are etc. are put into the data files (in a part known as the CCDPACK extension; note that for non-NDF formats this means the image headers).

There are two ways to enter this information into your data frame extensions, use either the PRESENT or IMPORT programs. If your data has the correct FITS headers then you use IMPORT to interpret these and if it has none (or the FITS headers do not give a complete description) you use PRESENT. Unless you have an existing FITS ``import control table'' for your detector (some of these are available with CCDPACK, check XREDUCE or REDUCE for a list of these) using IMPORT isn't a trivial task and you should probably opt for using PRESENT, even if you have some FITS information available. A description of how to create a FITS import control table is given in the IMPORT description.

Using PRESENT is fairly trivial as long as you've run CCDSETUP and answered all the relevant parts. PRESENT just requires lists of the data frames of each type and a filter type (any old value will do if this isn't relevant). So an invocation of PRESENT might be:

% present bias='bias*' target='ngc891*' flat='ff*'

although you'd generally run it and respond to the prompts interactively. CCDPACK programs can generally accept lists of data frames, so it this case it processes all the frames with names starting with bias as bias frames etc. Note that the expansion of the wildcard symbol ``*'' happens inside the program (and not by the shell as is usual) so it is protected by single quotes.

When running PRESENT it's a good idea to check the output to make sure that your frames are given the correct frame type. The known frame types are:

• TARGET: These are the frames with the real data. The ``target'' of your observations (or perhaps the target that the telescope points at).
• FLAT: The flatfields.
• BIAS: The bias frames
• DARK: Any dark count frames (not usual).
• FLASH: Any pre-flash frames (very unusual).

There are also several extra types that are used to define the calibration masters. These are MASTER_BIAS, MASTER_DARK, MASTER_FLAT and MASTER_FLASH. PRESENT can be used to import foreign masters (such as spectral flatfields).