ccdgroups: Group CCD images into image lists

Package: ccdred

Usage

ccdgroups images output

Parameters

images

List of CCD images to be grouped.

output

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:

ccdtype

Group by CCD image type.

subset

Group by subset parameter.

position

Group by position in right ascension (in hours) and declination (in degrees). The groups are defined by a radius parameter (in arc seconds).

title

Group by identical titles.

date

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.

Description

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".

Examples

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 ...]

See also

ccdlist, ccdtypes, instruments, subsets