[fitswcs] Grisms

[William Thompson]

But one can also fit the Grism function, and this is something one should be 
aware of when doing that.  The fifth paragraph of section 5.2 discusses 
adjusting the parameters to produce the best fit--that would be the best place 
to mention it.

Steve Allen wrote:
> Hi William,
> 
> On Fri 2005-04-22T15:28:40 -0400, William Thompson hath writ:
> 
>>Unless I've made a mistake anywhere, this should be discussed in the text.
>>If one tries to establish the 7 parameters by means of a least squares fit,
>>one ends up with a degenerate problem.  I anticipate that fitting would be
>>a common procedure--that's certainly what we do today, except that we
>>usually fit polynomials.
> 
> 
> This is addressed in the second paragraph of section 5 where we admit
> that the grism model does not address the full ray-tracing complexity
> of real spectrographs and that the table lookup and polynomial methods
> of paper IV may be preferable.
> 
> --
> Steve Allen          UCO/Lick Observatory       Santa Cruz, CA 95064
> sla at ucolick.org      Voice: +1 831 459 3046     http://www.ucolick.org/~sla
> PGP: 1024/E46978C5   F6 78 D1 10 62 94 8F 2E    49 89 0E FE 26 B4 14 93
> 
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> 

-- 
William Thompson
NASA Goddard Space Flight Center
Code 612.1
Greenbelt, MD  20771
USA

301-286-2040
William.T.Thompson.1 at gsfc.nasa.gov