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ccdgroups noao.imred.ccdred



ccdgroups -- Group CCD images into image lists


ccdgroups images output


List of CCD images to be grouped.
Output root group filename. The image group lists will be put in files with this root name followed by a number.
group = "ccdtype"
Group type. There are currently four grouping types:
Group by CCD image type.
Group by subset parameter.
Group by position in right ascension (in hours) and declination (in degrees). The groups are defined by a radius parameter (in arc seconds).
Group by identical titles.
Group by identical dates.
radius = 60.
Grouping radius when grouping by positions. This is given in arc seconds.
ccdtype = ""
CCD image types to select from the input image list. If null ("") then all image types are used.


The input images, possible restricted to a particular CCD image type, are grouped into image lists. The "ccdtype" or "subset" groups produce output image lists with the given root name and the CCD type or subset as an extension (without a period). For the other group types the image lists have file names given by the root output name and a numeric extension (without a period). If the package parameter ccdred.verbose is yes then the image name and output group list is printed for each image. The image lists can be used with the @ list feature for processing separate groups of observations. Note that grouping by CCD image type and subset is often not necessary since the ccdred tasks automatically use this information (see ccdtypes and subsets ).

Besides CCD image type and subsets there are currently three ways to group images. These are by position in the sky, by title, and by date. Further groups may be added as suggested. The title grouping is useful if consistent titles are used when taking data. The date grouping is useful if multiple nights of observations are not organized by directories (it is recommended that data from separate nights be kept in separate directories). The position grouping finds observations within a given radius on the sky of the first member of the group (this is not a clustering algorithm). The right ascension and declination coordinates must be in standard units, hours and degrees respectively. The grouping radius is in arc seconds. This grouping type is useful for making sets of data in which separate calibration images are taken at each position.

The date, title, and coordinates are accessed through the instrument translation file. The standard names used are "date-obs", "title", "ra", and "dec".


1. For each object 5 exposures were taken to be combined in order to remove cosmic rays. If the titles are the same then (with ccdred.verbose=yes):

    cl> ccdgroups *.imh group group=title ccdtype=object
    ccd005.imh  --> group1
    ccd006.imh  --> group1
    ccd007.imh  --> group1
    ccd008.imh  --> group1
    ccd009.imh  --> group1
    ccd012.imh  --> group2
    ccd013.imh  --> group2
    ccd014.imh  --> group2
    ccd015.imh  --> group2
    ccd016.imh  --> group2
    [... etc ...]
    cl> combine @group1 obj1 proc+
    cl> combine @group2 obj2 proc+
    [... etc ...]

Note the numeric suffixes to the output root name "group".

2. CCD observations were made in groups with a flat field, the object, and a comparison spectrum at each position. To group and process this data:

    cl> ccdgroups *.imh obs group=position >> logfile
    cl> ccdproc @obs1
    cl> ccdproc @obs2
    cl> ccdproc @obs3

Since no flat field is specified for the parameter ccdproc.flat the flat field is taken from the input image list.

3. If for some reason you want to group by date and position it is possible to use two steps.

    cl> ccdgroups *.imh date group=date
    cl> ccdgroups @data1 pos1
    cl> ccdgroups @data2 pos2

4. To get groups by CCD image type:

    cl> ccdgroups *.imh "" group=ccdtype
    ccd005.imh  --> zero
    ccd006.imh  --> zero
    ccd007.imh  --> zero
    ccd008.imh  --> dark
    ccd009.imh  --> flat
    ccd012.imh  --> flat
    ccd013.imh  --> object
    ccd014.imh  --> object
    ccd015.imh  --> object
    ccd016.imh  --> object
    [... etc ...]

Note the use of a null root name and the extension is the standard CCDRED types (not necessarily those used in the image header).

5. To get groups by subset:

    cl> ccdgroups *.imh filt group=subset
    ccd005.imh  --> filt
    ccd006.imh  --> filtB
    ccd007.imh  --> filtB
    ccd008.imh  --> filtB
    ccd009.imh  --> filtV
    ccd012.imh  --> filtV
    ccd013.imh  --> filtV
    ccd014.imh  --> filtB
    ccd015.imh  --> filtB
    ccd016.imh  --> filtB
    [... etc ...]


ccdlist, ccdtypes, instruments, subsets

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