This section provides a brief explanation of what the CCDPACK registration tasks (FINDOFF, PAIRNDF, CCDALIGN, IDICURS, REGISTER, WCSREG) do when they encounter input files with Set header information.
By the registration stage, it is no longer of direct interest what the source of each image is, only how it relates to the others, so the Set Index attribute is simply ignored by these programs. In fact the registration applications will ignore Set header information altogether unless a Set alignment coordinate system -- one with the special Domain name ``CCD_SET'' -- is attached to the image. Whether there is one or not will depend on whether the ADDWCS parameter was true when the Set headers were added with MAKESET. It will also disregard Set alignment if USESET=FALSE.
Only the Set Name attribute and the CCD_SET coordinate system are considered by these programs then. Since the CCD_SET coordinates are taken to represent a fixed and reliable alignment of images in the same Set, all images with the same Set Name are taken to be effectively glued together in those coordinates, and the registration programs will not take any steps to change the relative positioning of the images within a Set.
So the programs FINDOFF and REGISTER which deal in position lists will read in all the input images, construct a single superlist from the associated lists of all the members of the same alignment Set, and treat this as if it came from a single image. IDICURS, PAIRNDF and CCDALIGN, which display images in a GUI and allow the user to mark points on them, will display a whole Set at once for marking or sliding around rather than one NDF at a time. And WCSREG, which mediates between different coordinate systems to come up with a global registration using as many as necessary, accords maximum priority to alignment within a Set in CCD_SET coordinates, and will not allow any realignment to occur which conflicts with that. Of course images from different Sets are not considered to be aligned in their CCD_SET coordinates.
Once again, for most purposes you can just feed the list of
images to the programs and they will do the right thing.