System Requirements

1. You must have IDL installed.
   
2. You must have the IDL Astronomy User's Library installed in your IDL path.

Download the following files:

coad.pro
doall_coads.pro
bitget.pro

and place them in a directory in your IDL path.

1. Create a list of BCDs that you wish to combine. They should all be at the same nod or map position. For this example, call it 'bcdlist.txt'.
   
   
2. At the IDL prompt, type:

   IDL>coad, 'bcdlist.txt', /verbose, fatalbits=[8,12,13,14]

   (The /verbose argument is optional, as is the fatalbits argument, for which the default values are shown.)
   
   
3. Examine the output files, which end in 'coa2d.fits', 'c2unc.fits', and 'c2msk.fits'.

1. Create a list of BCDs for which you wish to create coadded images. They do not need to all be at the same nod or map positions. The procedure will figure out which BCDs should be combined based on their filenames. It will create a separate coadded image (with accompanying uncertainty and mask files) for each subset that shares the same module, aorkey, and expid. For this example, call the BCD list 'mixedbcdlist.txt'.
   
   
2. At the IDL prompt, type:

   IDL>doall_coads, 'mixedbcdlist.txt', /verbose, fatalbits=[8,12,13,14]

   (The /verbose argument is optional, as is the fatalbits argument, for which the default values are shown.)
   
   
3. Examine the output files, which end in 'coa2d.fits', 'c2unc.fits', and 'c2msk.fits'. For each 'coa2d.fits' file, a 'bcdlist.txt' file will also be created, so that the user can see which BCD files went into each 'coa2d.fits' file. The 'bcdlist.txt' files can also be used as input to coad.pro.