[Aavso-photometry] FITS Keyword standard

[Michael Newberry]

I don't know what other programs do, but I can tell you how Mira handles the 
mid-time in case anyone else wants to try it. If you combine a series of 
images then the computed mid-time of the sequence of exposures is stored as 
the keywords DATE-MID and TIME-MID. As per the FITS Y2K standard, both the 
date and time are merged into the DATE-MID keyword (the TIME-MID keyword is 
just thrown in in case the image is later loaded into an old-style FITS 
reader that wants to get the date and time separately). If you load a 
combined image for photometry, and you select "middle of exposure" as the 
time reference, then Mira looks for the DATE-MID keyword and uses its value 
for the reference time and the calculated Julian Date. Going back to the 
earlier discussion, DATE-MID and TIME-MID are thus "private" keywords that 
Mira creates and knows how to read and use, and they are based on the naming 
convention of the FITS date/time keywords like DATEOBS and DATEFITS.

Michael

----- Original Message ----- 
From: "Jim Jones" <nt7t at centurytel.net>
To: "AAVSO Photometry" <aavso-photometry at mira.aavso.org>
Sent: Thursday, January 03, 2008 10:19 AM
Subject: Re: [Aavso-photometry] FITS Keyword standard


>
> Arne
>
> I'm impressed.  But if ICE is terribly complex as compared to IRAF
> itself (which is of course a piece of cake) I think I'll pass ;>}
>
> My older ST7, uses EGAIN and EXPOSURE.  It also doesn't include
> RDNOISE.  I just checked my new ST8 and SBIG includes both EXPOSURE and
> EXPTIME, however it still uses EGAIN and doesn't include RDNOISE.  Since
> it appears that this is in the firmware of the camera, it may be an up
> hill battle to get it changed.  Probably the best you could hope for is
> to get both the legacy keyword and the correct keyword included in new
> cameras.
>
> The camera mfgs may be a bigger problem than the software vendors.
> MaxIm and AIP (and to the best of my memory Canopus) simply realize that
> SBIG uses some nonstandard keywords and take care of the problem for the
> user.
>
> It would also be nice to solve the MIDPOINT problem.  So far as I know,
> there is no official or unofficial standard for including the mid point
> of a stacked exposure.
>
> Good luck.
> Jim Jones
>
> arne wrote:
>> Michael Newberry wrote:
>>
>>> Jim,
>>>
>>> I appreciate what you are saying, and it is unfortunate that you have to
>>> make those extra steps. But that is not the fault of IRAF or MIRA. The
>>> programs you mention that control your camera or telescope need to clean 
>>> up
>>> any non-standard issues so they use the correct keywords to start with.
>>> There is no good served by having images that begin life with the wrong
>>> header structure---only extra work and gotchas downstream, as you have
>>> found. That's why there is *one* standard. You should pressure the 
>>> software
>>> vendor to adhere to it.
>>>
>>>
>> Several people have asked me to work with the software vendors and
>> get them to standardize on a common set of keywords.  This has been
>> painfully obvious to me while processing the NGC6811 images that
>> came from several different vendors.  I agree with Michael that there
>> are certain standard keywords, and vendors are doing a good job of
>> implementing them.  It is just the optional keywords where some
>> vendors use them, some invent their own, some use a different format,
>> etc.  I know what I need for photometry, and I know what the professional
>> community uses, and it really suprises me that vendors have ignored
>> the efforts of many professional astronomers.
>>
>> The standard data submission formats will be released about January 14.
>> I then will be spending the next week finishing the comparison star
>> database update, and then perhaps I can start a dialog on FITS with
>> the vendors.
>>
>> By the way, Jim, IRAF *does* do camera control, and was the first
>> image processing package to do so to the best of my knowledge.
>> The package is called ICE (Instrument Control Environment) and was
>> terribly complex to program, but several sites still use it.
>> Arne
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