Registering frames from a mosaic camera

Here we revisit the example in Section . By making use of the Set alignment coordinates we have described above, the same job can be done with less user effort.

As always when working with Sets, the first thing to do is to tell CCDPACK that Set headers are important:

% ccdsetup useset=true accept

The data files are the same as in the un-Setted example. This time however the first thing we do with them is to group the images into two Sets, one for each exposure. Using MAKESET's ASTFILE parameter we can import the saved AST file alignment information at the same time

% makeset in='1?' mode=list astfile=instrument.ast
% makeset in='2?' mode=list astfile=instrument.ast

These commands add a new coordinate system with the Domain (name) ``CCD_SET'' as well as suitable Set headers.

In this case we suppose that the AST file has been written to extract information about telescope orientation from suitable FITS headers (see the description of the FITSROT parameter of ASTEXP for more details). This simply means we can avoid adding a 180 degrees-rotated frame by hand.

We now perform the familiar automatic registration steps. First execute FINDOBJ, which pays no attention to Set headers and behaves just as usual.

% findobj in='"1?,2?"' outlist='*.find'

The FINDOFF program however takes special notice of the Set headers:

% findoff inlist='"1?,2?"' outlist='*.off'

    NDFs containing position lists     Current domain      Set Name attribute
    ------------------------------     --------------      ------------------
  1) 1a                                     CCD_SET        1a
  2) 1b                                     CCD_SET        1a
  3) 1c                                     CCD_SET        1a
  4) 2a                                     CCD_SET        2a
  5) 2b                                     CCD_SET        2a
  6) 2c                                     CCD_SET        2a

    Input position lists:
    ---------------------
  1) 1a.find
     1b.find
     1c.find
  2) 2a.find
     2b.find
     2c.find

     ...

    List  List  No. matches  Completeness  Status   Algorithm
    ----  ----  -----------  ------------  ------   ---------
     1     2      8          0.8714286     ACCEPTED    FAST

     ...

  Approximate offsets in image Current coordinates:

  List             X-offset                    Y-offset
    1)               +0.000000                   +0.000000
    2)             +164.066734                 +310.941234

    Output position lists:
    ----------------------
  1b.off
  1c.off
  2b.off
  2c.off

(much of the output is omitted here for reasons of brevity). What it has done is to construct one list for each Set, rather than one for each frame, on the assumption that the CCD_SET alignment is correct. Having worked out the offsets between the two ``superlists'', it writes and associates matched position lists for each of the files which would actually contain at least one of the matched points.

Finally, we can simply invoke REGISTER

% register inlist='"1?,2?"' fittype=1
  6 input NDFs accessed using parameter INLIST
  There is no associated list for NDF 1a.
  There is no associated list for NDF 2a.

    NDFs containing position lists     Current domain      Set Name attribute
    ------------------------------     --------------      ------------------
  1) 1b                                     CCD_SET        1a
  2) 1c                                     CCD_SET        1a
  3) 2b                                     CCD_SET        2a
  4) 2c                                     CCD_SET        2a

    Input position lists:
    ---------------------
  1) 1b.off
     1c.off
  2) 2b.off
     2c.off

    ...

  List 1)
    A =      +0.000000       B = 1                    C = 0
    D =      -0.000000       E = 0                    F = 1

  List 2)
    A =    +164.203695       B = 0.9999997            C = 0.0007688743
    D =    +310.941640       E = -0.0007688743        F = 0.9999997

Again it has constructed a list for each Set, and worked out the transformation coefficients between these. When it has successfully done this, every members of each Set which has been registered will be given a new CCD_REG coordinate system defining the registration, even those which did not have any associated position list (files 1a and 2a in the example above). For this reason there is no need to do extra work finding a global registration as in Section . Previewing (DRAWNDF), resampling (TRANNDF) and combining (MAKEMOS) can now be performed without further ado.

Again, once the Set alignment has been properly set up, the commands issued are the same as if there were no Sets, but by making use of the Set headers, CCDPACK is able to register groups of frames in which some have no overlap with any of the others.