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Mosaicing
Mosaicing is the name applied to the process by which images of
astronomical targets are combined in such a way that the positions of
the objects are matched up. This can also lead to a final image larger
than the input images if you are, for example, mapping out the IR
emission in an extended target. Different reduction packages have
several different methods for doing this, but all basically rely on
the user specifying the positions of the objects to be matched up from
one image to another, and/or specifying the relative shifts between
each image that has to be combined.
A series of commands in MIDAS are used to perform mosaicing, all included
in the CCDRED context.
CREATE/MOSAIC is used first to create a master frame including all the
subframes. Alignment of the frames is done using ALIGN/MOSAIC, and
background levels are matched using MATCH/MOSAIC and FIT/MOSAIC.
Objects to be used in matching the subimages together are selected using
the SHIFT/MOSAIC command. Overall parameters for the mosaicing
routines can be examined using SHOW/CCD MO and set using
SET/CCD MO.
More extensive documentation on the mosaicing routines is supplied
in the chapter on CCD reductions, Chapter 3.
Next: Further Off-line Analysis
Up: Off-line Reduction
Previous: Combining Images
Petra Nass
1999-06-15