[obs-tap]:updates on the Proposed recommendation + new document

[Arnold Rots]

Rob Seaman wrote:
> On Jul 8, 2011, at 6:36 AM, Arnold Rots wrote:
> 
> > Just two quick comments. Both highlight how this standard is still
> > heavily slanted toward optical images.
> 
> Undoubtedly true and such biases should be minimized.
> 
> > Mireille Louys wrote:
> > [ Charset ISO-8859-1 unsupported, converting... ]
> >> Dear Arnold, Dear all,
> >> 
> >>> o_stat_error is an interesting case. Since our unit is counts, the
> >>> proper value would be "POISSON"; I realize that that is not a double,
> >>> but what else can we give as a value?
> >> 
> >> 
> >> This was meant only for quantitative estimation of the error and does  
> >> not cover the statistical properties of the signal.
> > 
> > I realize that, but the problem is that one can't give a single
> > quantitative value in the case of Poisson noise. However, identifying
> > it as Poisson does immediately provide the value for each point in the
> > image.
> 
> Well, it provides a heuristic for making estimates of the
> error/noise/variance values.  That is certainly better than picking a
> scalar.  Even in the optical a purely scalar error is an artificial
> choose, see for example: http://arxiv.org/abs/0910.3733 
> 
> Negative numbers are presumably non-physical and could be used to
> encode special values corresponding to "POISSON" or even
> "POISSON+GAUSSIAN" with the absolute value representing the scalar
> gaussian contribution (e.g., read noise + sky noise). 
> 
> Might consider providing the error as a variance, too.
> 
> Rob
> 

So, which of the three options should I choose for o_stat_error:

1. Return "POISSON"
2. Return -1 (or some other negative value) that by convention will
   mean "POISSON"
3. Do not return o_stat_error (i.e., don't provide any information on
   it)

  - Arnold

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Arnold H. Rots                                Chandra X-ray Science Center
Smithsonian Astrophysical Observatory                tel:  +1 617 496 7701
60 Garden Street, MS 67                              fax:  +1 617 495 7356
Cambridge, MA 02138                             arots at head.cfa.harvard.edu
USA                                     http://hea-www.harvard.edu/~arots/
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