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[fitsbits] question about WCS keywords for pixel list
According to Table 2 in WCS Paper I, all the keywords for the pixel list
representation of an image include the table column number as part of the keyword name. This description agrees with the example in Table 10 of WCS Paper II. It seems to me, however, that several of these keywords should include the world coordinate axis number rather than the column number. I checked the "unofficial errata" for Papers I and II but didn't find any mention of this. Consider the case of a time-tag table containing columns TIME, X, and Y, which are respectively the time when a photon was detected and the pixel coordinates in a 2-D image where it was detected. To use a specific example, suppose the world coordinates are right ascension and declination. The reference pixel keywords are TCRPX2 and TCRPX3, giving the column numbers of the X and Y columns. But shouldn't the keywords for the world coordinates at the reference pixel be TCRVL1 and TCRVL2 rather than TCRVL2 and TCRVL3 (and similarly for several other keywords)? The WCS papers say the latter keywords are the ones to use, but it would be more consistent with the keywords for an image in the primary array if the former keywords were used. Phil |
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