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[fitsbits] CRPIX clarification
On Mon 2008/06/16 08:20:03 CST, Eric Greisen wrote in a message to: Mark Calabretta and copied to: William Pence , FITSBITS fitsbits@nrao. edu I did not like the former wording since random groups does have a regular lattice with WCS under the same rules as images along with the random parameters which need not have rules. For those not familiar with random groups, Eric refers to the regular array that follows the random parameters, these have world coordinates described in the conventional way using CRPIXn, CRVALn, CDELTn, and CTYPEn. On the other hand, my comment refers to the random parameters themselves. These store the world coordinate directly in PTYPEn and do not form a regular structure. To clarify that, the statement could be changed to "(e.g. as is done for the random parameters using PTYPEn in random groups data)". The whole point is that they are *random*, i.e. don't form a regular structure, and so provide an excellent contrast to the regular lattice structure associated with images. Regards, Mark |
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