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[fitsbits] CRPIX clarification



 
 
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Old June 17th 08, 03:16 AM posted to sci.astro.fits
Mark Calabretta
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Posts: 42
Default [fitsbits] CRPIX clarification


On Mon 2008/06/16 17:36:27 MST, Rob Seaman wrote
in a message to: Mark Calabretta
and copied to: Eric Greisen , FITSbits ,
William Pence

Dear Rob,

The question is whether this discussion of randomness adds anything to
the specific paragraph.


I believe it is useful to explain one thing by pointing out the
distinction with another. If the reader doesn't know anything about
random groups data then they can read over it. (That's why it's in
parentheses.)

BTW, "random" is not an apt description, "irregular" would have been
better.

Isn't the distinction here between a
repeating lattice and an individual datum, not between regular and
random structure?


The distinction is between defining a rule for computing the world
coordinates of each datum, and recording the world coordinates of
each datum.

In the former case, neither pixel coordinates nor world coordinates are
recorded. Pixel coordinates are inferred from array indices and that
is only possible because the data form a regular lattice.

That is not possible for the random parameter component of random groups
data because they are not regular. Therefore, you have to record the
world coordinate of each datum, or more usually, each array of data.
That is what the random parameters themselves are.

Regards, Mark


 




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[fitsbits] CRPIX clarification Mark Calabretta FITS 0 June 17th 08 01:12 AM
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[fitsbits] CRPIX clarification Rob Seaman FITS 0 May 30th 08 09:16 AM


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