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[fitsbits] CDELTn
This is essentially right, although I was probably the one originally
responsible for this. In the case of CDi_j the more logical default is probably the unit matrix (diagonal elements 1.0, off-diagonal 0), but the more global default for generic missing keywords was/is zero if not present. - Doug On Fri, 21 Sep 2007, Mark Calabretta wrote: On Thu 2007/09/20 11:51:24 -0400, Phil Hodge wrote in a message to: Mark Calabretta I presume you meant CDELTia rather than CRVALia. I've never understood why, but WCS Paper I actually specifies that the default value for any CDi_ja keyword is zero (although if all of them are absent the PC form is assumed). This was the de facto interpretation of CDi_j before it was made standard by Paper I. If I remember correctly (not wanting to search through 1000s of old emails) it was supplied by Frank Valdes and Lindsay Davis by interpretation of the IRAF code which was considered to be the defining instrument. So effectively it's for historical reasons. Cheers, Mark _______________________________________________ fitsbits mailing list http://listmgr.cv.nrao.edu/mailman/listinfo/fitsbits |
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