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diff --git a/noao/imred/ccdred/doc/subsets.hlp b/noao/imred/ccdred/doc/subsets.hlp new file mode 100644 index 00000000..78aafb01 --- /dev/null +++ b/noao/imred/ccdred/doc/subsets.hlp @@ -0,0 +1,99 @@ +.help subsets Jun87 noao.imred.ccdred +.ih +NAME +subsets -- Description of CCD subsets +.ih +DESCRIPTION +The \fBccdred\fR package groups observation into subsets. +The image header parameter used to identify the subsets is defined +in the instrument translation file (see help for \fBinstruments\fR). +For example to select subsets by the header parameter "filters" the +instrument translation file would contain the line: + + subset filters + +Observations are generally grouped into subsets based on a common +instrument configuration such as a filter, aperture mask, +grating setting, etc. This allows combining images from several +different subsets automatically and applying the appropriate +flat field image when processing the observations. For example +if the subsets are by filter then \fBflatcombine\fR will search +through all the images, find the flat field images (based on the +CCD type parameter), and combine the flat field images from +each filter separately. Then when processing the images the +flat field with the same filter as the observation is used. + +Each subset is assigned a short identifier. This is listed when +using \fBccdlist\fR and is appended to a root name when combining +images. Because the subset parameter in the image header may be +any string there must be a mapping applied to generate unique +identifiers. This mapping is defined in the file given by +the package parameter \fIccdred.ssfile\fR. The file consists of +lines with two fields (except that comment lines may be included +as a line by itself or following the second field): + + 'subset string' subset_id + +where the subset string is the image header string and the subset_id is +the identifier. A field must be quoted if it contains blanks. The +user may create this file but generally it is created by the tasks. The +tasks use the first word of the subset string as the default identifier +and a number is appended if the first word is not unique. The +following steps define the subset identifier: + +.ls (1) +Search the subset file, if present, for a matching subset string and +use the defined subset identifier. +.le +.ls (2) +If there is no matching subset string use the first word of the +image header subset string and, if it is not unique, +add successive integers until it is unique. +.le +.ls (3) +If the identifier is not in the subset file create the file and add an +entry if necessary. +.le +.ih +EXAMPLES +1. The subset file is "subsets" (the default). The subset parameter is +translated to "f1pos" in the image header (the old NOAO CCD parameter) +which is an integer filter position. After running a task, say +"ccdlist *.imh" to cause all filters to be checked, the subset file contains: + +.nf + '2' 2 + '5' 5 + '3' 3 +.fi + +The order reflects the order in which the filters were encountered. +Suppose the user wants to have more descriptive names then the subset +file can be created or edited to the form: + +.nf + # Sample translation file. + '2' U + '3' B + '4' V +.fi + +(This is only an example and does not mean these are standard filters.) + +2. As another example suppose the image header parameter is "filter" and +contains more descriptive strings. The subset file might become: + +.nf + 'GG 385 Filter' GG + 'GG 495 Filter' GG1 + 'RG 610 Filter' RG + 'H-ALPHA' H_ALPHA +.fi + +In this case use of the first word was not very good but it is unique. +It is better if the filters are encoded with the thought that the first +word will be used by \fBccdred\fR; it should be short and unique. +.ih +SEE ALSO +instruments +.endhelp |