Re: Data Disk Format

[Tom Droege <tdroege@veriomail.com>]

I am just trying to point out that there is a format error somewhere.  I am 
writing 16bit signed integers in the raw data file.  RawToFits does 
something with them, I do not know what, and previously this has not seemed 
to be a problem for anyone.  At this point, I do not care that the .fts 
header is wrong.  It is no doubt wrong.  The problem of the day is to 
figure out how to use existing programs to analyze existing data.

I am doing my best to use the full range of my 16 bit signed ADC.  So I 
have set zero at about -25000 counts.  I am not claiming to be a 
spotlight.  ;^)

The real data then goes from the vicinity of -25000 counts for the 
pedestal, to 32767 for saturated full scale.

Tom Droege

At 01:44 AM 12/23/00 +0800, you wrote:
>Yes, it is one of the most common 'gotchas' of FITS. There was
>a section in the FITS FAQ about this.
>
>For some reason, FITS does *NOT* have a 16bit unsigned data type
>in it. But ( from memory ) the SBIG wrote 'FITS' files that way
>anyway!
>
>With good astro ADs being 12 bit, or there abouts, a 16 bit unsigned
>would seem a natural show in. Well, I was a comitee I guess.
>
>Quick sanity check; you should never see a negative data point
>in the raw data. Never. This would mean your telescope was acting
>as a spotlight!
>
>--
>~paul
>Paul Repacholi                               1 Crescent Rd.,
>+61 (08) 9257-1001                           Kalamunda.
>                                              West Australia 6076
>Raw, Cooked or Well-done, it's all half baked.